document_title: Pretty Little Liars (book series)

question_text: what is the first book of pretty little liars

text: Pretty Little Liars (book series)

text: Overview[edit]

text: The series is loosely divided into four arcs, chronicling the introduction and reveal of each "A". Set in the suburbs of Philadelphia, the series follows the lives of four teenage girls nicknamed the Pretty little Liars or simply the Liars, whose clique falls apart after the disappearance of their Queen bee leader, "Alison DiLaurentis". Three years after her disappearance, the girls begin receiving threatening messages from an anonymous character named "A," who threatens to expose their secrets, including long-hidden ones they thought only Alison knew. Shortly after the messages begin, Alison's body is discovered buried in her yard. The books progress with the four girls trying to figure out the identity of "A" and facing many dangerous obstacles and twists as they do so.

text: Characters[edit]

text: The series has many characters, most of them recurring. The main characters are:

text: Spencer Hastings: Spencer is a headstrong, intelligent, overachieving girl who comes from the wealthy Hastings family.

text: Hanna Marin: Hanna is the bubbly, strong, and fierce "it-girl" of the group following Alison's disappearance. She suffers from an eating disorder, about which she received taunts from Alison.

text: Aria Montgomery: Aria is a quirky and artsy girl who, at the beginning of the books, is trying to find herself.

text: Emily Fields: Emily is considered the jock of the group, being a physical, loyal girl who struggles with her sexuality.

text: Alison DiLaurentis: Alison is the former "Queen Bee" of her clique, consisting of Spencer, Hanna, Aria and Emily. She had supposedly been killed at the beginning of the series however is revealed to have been alive and also their tormentor "A" as she was mistaken for her twin sister Courtney who pretended to be like her and was sent to The Preserve at Addison-Stevens, which she believed was the Liars' fault and has been plotting revenge ever since.

text: Her identical twin sister Courtney DiLaurentis is not crazy but she debuted inWanted after the TV show began in 2010. In the prequel, Courtney-as-Ali started disappearing in the last chapter and getting almost killed numerous times, until the end of the series (Vicious) when Ali-as-Courtney came out and started becoming friends with her twin "Ali" again after rehab with Iris and Tabitha, two lookalikes of Ali, all in the penultimate chapter.

text: In the book, their older brother's name is Jason DiLaurentis and their half-sisters are Melissa and Spencer Hastings.

text: Courtney DiLaurentis: Alison is really Courtney in the books. She used to be sweet, until she started pretending to be her twin, where her personality morphed into her. She is the third child to Jessica and Kenneth and was sent to The Preserve at Addison-Stevens after a physical argument with Alison who she eventually turned into and befriended the Liars up until the night of her infamous disappearance when she was killed and buried by the real Alison DiLaurentis and her accomplice Nick Maxwell.

text: A: A is the main antagonist of the series, being, for the most part, an anonymous character who relentlessly torments many characters, in particular the Liars. Mona Vanderwaal, Alison DiLaurentis and Nick Maxwell are discovered to be A. Mona became A due to Alison and the Liars being responsible for The Jenna Thing, which burned her too. However, she is killed when Spencer pushes her off a cliff face and her neck is caught between rocks. However, a new "A" rises, this time even more determined to hurt the Liars. This A is revealed to be Alison herself who wanted revenge on the Liars for ruining her life and Nick, who is revealed to be her accomplice.

text: Novels[edit]

text: First Arc[edit]

text:
Book #

Title

Publication Date

ISBN

Pages

1
Pretty Little Liars
October 3, 2006
978-0-06-088730-8
304

The story introduces an exclusive group of friends: Alison DiLaurentis, the popular yet manipulative queen bee; Aria Montgomery, an independent girl who is considered to be the oddball in Rosewood who also went to Iceland for the summer; Emily Fields, a swimmer who holds secret feelings for Alison; Hanna Marin, who strives to be thin and popular like Alison; and Spencer Hastings, an overachiever who is brave enough to stand up against Alison's manipulative ways. Alison mysteriously disappears during a sleepover with the girls in the summer before 8th grade.
The story then jumps 3 years later, when the girls are living their own lives and don't speak to each other.
Aria returns to Rosewood from a 3-year trip to Iceland with her family and comes back much more sophisticated than before she left. She meets and makes out with a guy in a local bar who is revealed later to be her English teacher, Ezra Fitz.
Emily befriends the new girl in town, Maya St. Germain, and soon develops romantic feelings for her, even though Emily has a boyfriend, Ben. Ben later finds Maya and Emily kissing in the photo booth at a party and dumps beer on them.
Hanna is the new popular girl in town alongside the former nerd, Mona Vanderwaal. However, she and Mona sometimes shoplift though both can clearly afford their steals. Hanna battles the urge to turn back to bulimia, and struggles to manage the stress of keeping her queen bee status.
Spencer continues to struggle in her long-standing rivalry with Melissa Hastings, her perfect older sister. Problems occur when she begins to feel attracted to Melissa's new boyfriend, Wren Kim.
Throughout the story, the liars get messages threatening to reveal their secrets of the present and past, including a terrifying incident the girls refer to as "The Jenna Thing". They automatically believe it is their missing friend, Alison, because she is the only one each of them confided in regarding their darkest secrets. However, they are shocked when the police find her corpse buried in the gazebo of her former house. The book ends with the liars receiving a text at Alison's funeral saying, "I'm still here, bitches. And I know everything. -A ". The girls have made up at this point.

2
Flawless
March 27, 2007
978-0-06-088733-9
330

Spencer Hastings, Hanna Marin, Aria Montgomery, and Emily Fields continue to receive text messages from an unknown person, "A", and are more desperate than ever to discover the identity of "A", who is still taunting them with the threat of exposing their many secrets. At first the girls think "A" is Alison, because she is the only person who knew their secrets, but then they start to believe the person behind the threats is Toby, because some messages they receive refer to 'The Jenna Thing' and with Alison dead, he is the only other person who was a part of the incident, although everyone but Spencer is unaware of why he took the blame for what happened to Jenna.
"The Jenna Thing" is revealed to be an incident in which Ali had set off a stink bomb in Jenna Cavanaugh's step-brother Toby's treehouse to get revenge after supposedly spying on her, only to see the treehouse burst into flames, not knowing that Jenna was inside, and due to that, she was permanently blinded. Toby was framed for the garage fire by Alison.
"A" sends Emily a text message hinting that "A" knows about Emily and Maya's romantic relationship and threatens to tell everyone about it. Emily becomes close with Toby and goes to a big benefit party with him but then later tells him that she thinks she might be gay.
"A" leaves a note for Hanna that forces her to tell Naomi and Riley that she makes herself throw up and that Sean was the one who broke up with her. Later on, she receives a text that tells her Sean is at Foxy with another girl. Hanna is shocked to discover her former boyfriend Sean Ackard ignoring his Virginity Club vows and nearly having sex with Aria.
"A" continuously tells Aria to either 'get rid of the problem' or to tell her mom the truth about Byron, her father, that he is seeing another woman. Aria goes to confront the other woman, Meredith, but when she does Meredith tells her that she and Aria's father are in love. Ella finds out that Byron is having an affair with a student named Meredith Gates and kicks him out, leaving Ella and Aria's mother-daughter relationship shattered.
Spencer continues to date with her sister Melissa's now ex-boyfriend Wren and later loses her virginity to him. However, Melissa starts to hook-up with him as well and eventually makes sure that he will be out of both of their lives for good.
Emily blames herself for Toby's suicide. In this book it is revealed that Toby was forcing himself on Jenna when they were in middle school and Ali and Spencer were the only ones who knew about it, which is how Alison forced Toby to take the blame.

3
Perfect
August 21, 2007
978-0-06-088736-0
298

Now homeless, Aria goes to live with her new boyfriend, Sean Ackard. Still seeing Ezra, their relationship is broken up when Sean informs the police, having found out the secret from "A".
Emily plans to go to the police to stop "A", which leads to "A" taking revenge by outing her to the whole school. Emily's parents threaten to send her away if she does not attend a "de-gaying" program, however, Emily realizes she can't change who she is.
Spencer is nominated for a Golden Orchid Award for the essay she copied from her sister Melissa, which "A" threatens to expose. Spencer's family discovers she cheated on her Golden Orchid essay, but keep it quiet to protect their reputation. Spencer comes to believe she might have killed Alison after discovering she suffers from rage-induced blackouts.
Hanna and Mona get into a fight, and Hanna seeks comfort with an "uncool" boy named Lucas. She goes to Mona's birthday party but gets humiliated, but she receives a text from "A" and recognizes the number. She intends to reveal the true identity of "A" to the other girls, but is run down by "A" before she can do so. The girls recognize it is A from the eerie text: She Knew Too Much-A

4
Unbelievable
May 27, 2008
978-0-06-088739-1
335

Hanna barely survives being rundown by "A", and due to a head injury, she loses her memory of the previous day, thus forgetting "A"'s identity.
Emily's parents catch her with Maya at a party and send her to Iowa to live with her strict, religious relatives. She is glad to be safe from "A", but after Emily is accused of threatening her cousins, she runs away. Emily returns home when she sees her parents on TV, who tell her that they love her and accept her for who she is. Emily and Maya are reunited, but Trista, a girl who Emily had met and flirted with in Iowa comes to visit, their relationship is shattered, and Emily is saddened further when she sees Trista and Noel hooking up.
After being kicked out of Sean's house, Aria reluctantly moves in with Byron and Meredith, who announces that she is pregnant and when Bryon's and Ella's divorce is finalized, they are to be married. While at Hollis College, Aria takes an art class and befriends Jenna, who she suspects could be "A".
"A" reveals to Melissa (Spencer's sister) that Spencer stole her essay for the Golden Orchid competition, but the family keeps quiet to protect their reputation. Melissa and Spencer grow closer, and Spencer confesses that she kissed Ian, and that he and Alison were secretly dating. When fragments of her memory from the night Alison died are restored, Spencer is horrified when it dawns on her that she may have accidentally killed Alison.
Mona and Hanna's friendship is restored, and to celebrate Hanna's recovery, Mona and Spencer plan a party for her. Spencer is surprised to discover that she enjoys Mona's company, and even more so when Mona tells her that she has been receiving messages from "A". Hanna is thrilled that Spencer approves of Mona, and they consider letting her join their clique.
"A" tells Aria that Meredith has a secret job at Hooters, and she goes there with Mike, only to discover that "A" was lying. Darren Wilden and several other cops are there, and Aria is tempted to tell them about "A". When Mike realizes that something is troubling his sister, he urges her to tell Darren, and she eventually does. On the night of Hanna's party, Aria tells Jenna what happened the night she was blinded and apologizes for not stopping Alison, but Jenna reveals that she and Alison had planned it together to get rid of Toby. Aria asks Jenna about "A", but Jenna becomes scared and quickly leaves, hinting that she knows who "A" is.
Melissa confronts Spencer about seeing Ian behind her back, which Spencer denies, and when she leaves, Spencer and Mona discover another note from "A" and suspect that Melissa killed Alison because she was jealous of her relationship with Ian. They inform the others, and decide to turn Melissa in. Mona drives Spencer to the police station, and Aria tells Emily and Hanna the truth about The Jenna Thing. When Hanna says that one in four boys sexually abuse their sister, Emily tells her not to believe everything she hears, which causes Hanna's memory to return, and she is horrified when she remembers who "A" is: Mona.
Spencer is hesitant about turning in Melissa, but Mona comforts her and convinces her otherwise. Moments later, Spencer receives a text from Emily, telling her that Mona is "A". When she receives several more from the girls, who are worrying about what Mona will do, Mona realizes that they finally figured it out. While Aria, Emily and Hanna go to the police station to tell Darren that Mona is "A", Mona drives Spencer to Floating Man's Quarry, where she explains that she saw what happened on the night of The Jenna Thing, and when Maya moved in, she found Alison's diary, which contained the girls' secrets. Using the information to her advantage, she got a new phone and became "A" to get revenge on the girls for blinding Jenna. Spencer accuses Mona of killing Alison, but Mona says that it was Ian who killed her, as Alison had blackmailed him about their relationship.
Spencer secretly calls Darren, who overhears her conversation with Mona and learns of their location. Mona tells Spencer that she originally planned to frame her for Alison's murder, but recently grew to like her, and thus decided to frame Melissa to do Spencer a favor. She then offers Spencer her life in return that she becomes "A" with her, as they could pin the blame on someone else. Spencer refuses and Mona attacks her. They fight on the cliff's edge, and in the struggle, Spencer accidentally pushes Mona off the cliff to her death. Aria, Emily and Hanna arrive on the scene with Darren and police, and find Mona's body and an unconscious Spencer.

text: Second Arc[edit]

text:
Book #

Title

Publication Date

ISBN

Pages

5
Wicked
November 25, 2008
978-0-06-156607-3
310

A new "A" begins making threats. Ian denies being Ali's killer.
Emily finds herself confused about her sexuality once again, as she now has feelings for a boy she met at church, Christian singer Isaac. Emily tries to date Isaac without him finding out about her orientation, though "A" keeps interfering. Emily tells Isaac about Maya and he then hugs her and tell her that he accepts her for who she is.
Hanna, still overcome with shock after discovering Mona Vanderwaal was really "A", can't seem to catch a break. She now has trouble with her stepsister Kate Randall. At a party at a hotel opening, Hanna and Kate continue to fight over title of "Queen Bee". Hanna and Lucas break up after Hanna tells everyone that Kate has herpes at a party to sabotage her. Eventually, Hanna's father forbids her from talking to anyone except Kate.
Aria has feelings for a man, Xavier, who she met at an art show; however, he ends up meeting and dating her mother through an online match site. This puts her at risk of hurting her mother again and further damaging their newly repaired relationship. Aria moves in with Meredith and Byron to avoid Xavier as his true intentions will jeopardize Aria and Ella's relationship.
After a shock at her gran's will reading and her family neglecting her, Spencer comes to believe that she is adopted and starts searching a reuniting website for answers.
In the end, Spencer, Emily, Aria, and Hanna find Ian's body in the woods behind Spencer's house, but when they return with the police, the body is missing. Wilden sort of pushes it off, and begins the search hours after the girls had shared their story.

6
Killer
June 30, 2009
978-0-06-156611-0
321

The girls discover that the person they think is Ali's murderer — Ian Thomas — has actually been framed, and they start to wonder if the new "A" really wants to threaten them or just to solve the mystery.
Spencer meets a woman named Olivia Caldwell who she thinks is her real mother, and attempts to move to New York, but it turns out to be a scam and she loses her college money.
Hanna and Kate compete for the affections of Aria's brother Mike Montgomery.
Aria falls in love with Jason DiLaurentis again.
Emily has sex with her new boyfriend Isaac, whose mother finds out and banishes Emily from their house without Isaac knowing. At the opening party for Radley, a former so-called "haven for troubled youth", Emily finds proof that Jason DiLaurentis had been a patient there, and soon Hanna, Aria, and Emily all come to believe that Jason and Darren Wilden had something to do with Ali's murder.
Ian Thomas confirms their suspicions about Darren and Jason right before someone sets the woods behind Spencer's house to fire. Although at first they had their doubts about Ian being alive, they are now confident he is.
While Aria is trying to get to Spencer's barn to show them Ali's flag from 6th grade, she finds someone caught in the woods because of the fire, saves this person, and then they all recognize her as Ali.

7
Heartless
January 19, 2010
978-0-06-156614-1
274

After the fire, no one believes the girls when they insist that they saw Alison.
"A" sends Emily to Lancaster, where Emily comes to believe that Ali was not the girl in the hole, but that Wilden has murdered a girl named Leah and covered it up by making it seem like it was Ali.
Aria begins a relationship with Noel Kahn, after he defends her at a party. She visits a medium, who produces a message in Ali's handwriting that states that "Ali killed Ali." This leads her to believe that Ali might have committed suicide.
Hanna's father sends her to a clinic to prevent her eating disorder from reappearing due to stress, where she befriends a troubled girl named Iris. Hanna has more dreams about Ali, which causes her to suspect that Iris had something to do with Ali's death.
"A" reveals to Spencer that her father had an affair (and that Alison is Spencer's half-sister), making her suspicious of her mother.
The Liars are arrested for Ali's murder. They realize that "A" has tricked each of them into believing someone else killed Ali. However, a man named Billy Ford is soon arrested for murdering Alison and Jenna Cavanaugh. Everyone now believes Ian is dead.

8
Wanted
June 8, 2010
978-0-06-156617-2
259

Aria, Hanna, Emily and Spencer are shocked to learn of the existence of Alison's twin sister, Courtney, when she's introduced at a press conference. Courtney had spent her life in institutions due to "health issues" and her existence was kept secret by her family. It is revealed that Jason was not a patient at the Radley but instead he was visiting Courtney. She was finally released and went home to Rosewood, where she attempts to resume her sister's life and begins tentative friendships with Ali's old friends. She later reveals that she's actually Ali, the real Courtney had pretended to be her on the night of Ali's disappearance, and she was the one who was killed. When she had tried to tell her family who she was, they didn't believe her because Courtney was notorious for pretending to be Ali, and sent her back to the institution in Courtney's place. The girls are thrilled that Ali is back, and jump at the chance to go with her to the family's house in the Poconos after a school dance.
On the way there, Spencer gets a frantic call from her mother telling her that Melissa has disappeared. Spencer had begun to believe that her sister was the one who killed Ali and that she may be after the rest of them, but once they arrive at the house it's revealed that Ali is the killer. They discover that the girl they were friends with years ago was actually Courtney, and the real Ali was stuck in an institution. She had killed Courtney for ruining her life, attempted to kill the girls in the forest fire, tried to have them arrested, and is now going to kill them by setting the house on fire.
They're able to escape after stumbling onto Ian's body hidden in a closet and releasing a bound Melissa, who Ali had kidnapped and was planning to kill as well. Ali is trapped inside the house and it's assumed she died in the fire, although her body is never found.
After learning that her ex-husband shipped Hanna off to a mental institution, Ashley Marin transfers back to Rosewood and kicks Hanna's father, Isabel and Kate out of the house, thrilling Hanna. Hanna and Mike get back together.
Meredith goes into labor, giving birth to a girl named Lola. Aria and Noel get back together after it is revealed that Ali kissed him, not the other way around, and Ella breaks up with Xavier after learning of his inappropriate behavior towards Aria.
Spencer's father proclaims that even though he and her mother may not get back together, things are going to change for the better in their family, and Spencer and Melissa grow closer after almost being killed.
Emily buries everything she can find that reminds her of Ali at Courtney's grave, hoping she can finally find closure, but is unsure of whether the noises she hears at the cemetery are real or imagined. And somewhere, a new girl starts her senior year at an anonymous school, a girl whose name just so happens to be an anagram of Alison DiLaurentis. The reader is left wondering if Alison is alive.

text: Third Arc[edit]

text:
Book #

Title

Publication Date

ISBN

Pages

9
Twisted
July 5, 2011
978-0-06-208101-8
305

The book begins with the girls vacationing in Jamaica and Emily seeing a girl who she believes is Ali. Throughout the rest of the book, details about that fateful vacation emerge.
In the meantime, Noel, Aria's boyfriend, has an exchange student, from Finland, come to live with him. Instead of being the nerdy boy, Klaudius, that Noel expected, the exchange student turns out to be a gorgeous blonde, Klaudia, who tries to steal Noel from Aria. Aria ends up accidentally pushing Klaudia off of a ski lift as an act of self-defense; however, Klaudia uses that information against Aria. By that point, Aria and Noel's relationship is shaky and uncertain.
Emily meets a new girl, Chloe, who moves into the Cavanaugh's old house. They immediately become good friends, bonding over Chloe's baby sister, Grace. Emily has now given up hope of getting a swim scholarship, her only option for college. Chloe's dad offers to help but also hits on Emily, even making sexual moves towards her. Chloe walks in on her dad kissing Emily, but thinks that it's Emily who is wrecking her family (her father had previously been cheating).
Hanna's dad runs for senator of Pennsylvania. Patrick, somebody who's helping out at the set, offers Hanna a modeling job, but he takes some naughty pictures and threatens her with them, saying he will release them to the public and ruin her dads' chances of becoming senator, unless she gives him $10,000. Hanna steals money from her dad and frames Jeremiah, a mean man who is also working on set.
Spencer's mom has begun to date Nicholas Pennythistle, the father of snobby Amelia and her brother Zach, in whom Spencer develops a romantic interest. When they go out dancing, she kisses him, only to find out Zach is gay. When the Hastings and Pennythistles travel to New York together, Spencer and Zach drunkenly fall asleep in the same bed. During the night, Spencer had kicked off her clothes because she was hot, leaving her in her blouse and underwear. The next morning Mr. Pennythistle wakes them both up by entering the room. Their indecent clothing and close proximity leads Mr. Pennythistle to believe that they had slept together and acts violent. Spencer tells him that Zach didn't touch her and that he's gay, hoping to help, but Mr. Pennythistle becomes furious and sends Zach to military school. Zach and Spencer's friendship ends, Zach leaving Spencer with the words "Rot in hell, bitch".
The girls start to get messages from a new "A", and believe it's Ali and that she somehow survived the fall from the building. In the end of the book, the news turns on and a teenage girl's dead body was found floating in the water in Jamaica. They identify this girl as Tabitha Clark from New Jersey. The cops believe her death was a tragic accident - not a murder. The girls realize they killed an innocent girl.

10
Ruthless
December 6, 2011
978-0-06-208186-5
338

It is revealed that last summer while Spencer was taking AP courses at Penn, she began taking speed pills as a way to help with studying. After being arrested by the police for possession, she arranges for Hanna to help her frame her roommate, Kelsey, as a dealer, in order for Spencer to not face charges. After landing the role of Lady Macbeth in the school play, the stress and guilt begin to take their toll on Spencer, causing her to have frequent hallucinations in which she is haunted by Kelsey and Tabitha. She becomes paranoid and begins to believe Kelsey is "A" and is taking revenge on her for being framed.
Emily accidentally meets Kelsey at a party and is instantly smitten with her. She and Kelsey grow close, much to Spencer's disapproval. After Emily is hurt by Spencer's remarks about her love for Alison, she angrily tells Kelsey that Spencer framed her for the drug possession. Depressed, Kelsey overdoses and attempts to throw herself into the quarry where Mona died, but Emily saves her and Kelsey is sent to the Preserve for treatment. While visiting Kelsey, the girls realize that Tabitha was also a patient at the Preserve and was the same age as Alison and Courtney.
Hanna's father asks her to help with the social media aspect of his campaigning. She meets a boy named Liam, who she falls for, despite knowing he is the son of her father's political opponent. They break up when she learns he has been seeing multiple other girls while dating her, and reconciles with Mike.
After Aria is dumped by Noel, she seeks out comfort in Ezra, in hopes of rekindling their romance. However, things are strained between them, and Aria eventually goes back into a relationship with Noel, after discovering Ezra and Klaudia being intimate.
The Liars attempt to circumvent "A's" threats by coming clean about their secrets, with varied success. Meanwhile, "A" becomes more violent, shoving Emily down a hill at Stockbridge trail. "A" sends Spencer an email of Tabitha on the beach with a head injury, indicating that "A" was the one who disposed of Tabitha's body. "A" taunts the Liars, stating they will never discover "A's" true identity. Kelsey cannot be A. Emily and Spencer have their biggest rivalry.

11
Stunning
June 5, 2012
978-0-06-208189-6
302

The Liars begin to suspect a woman, Gayle, might be "A", when she comes to Rosewood and begins to harass them; it is revealed that Emily backed out of a deal to let Gayle adopt her daughter in exchange for $50,000 paid under the table. Emily finds herself reconnecting with Isaac while attempting to tell him about her pregnancy, but she fears the repercussions of such a confession.
Spencer visits Princeton hoping to join an Eating Club, but "A" interferes and spikes Spencer's pot brownies with LSD and Ritalin.
Aria panics when she finds out Noel's father is a drag queen and ends up putting her relationship with Noel at risk when "A" threatens Aria to expose Noel's father photo publicly.
On a tip from "A", Hanna begins spying on Mike's new girlfriend, Colleen. Later she becomes publicly humiliated by "A" when she sends everybody a video of Hanna stalking Colleen, and her desperate ways of getting Mike back.
Gayle is murdered by "A" and it is revealed that she was Tabitha's stepmother. Tabitha's father speaks at Gayle's funeral, and announces that Tabitha's autopsy showed no trace of alcohol, meaning that she was murdered. He thus plans to re-open the investigation into her death, and threatens the killer that he will find him, both Gayle's and Tabitha's killer. The girls get very nervous about this.

12
Burned
December 4, 2012
978-0-06-208192-6
319

It is revealed that prior to the events of Twisted, the Liars covered up Hanna's involvement in a car accident that left another girl, Madison, badly injured. While on a school-sponsored cruise in the Caribbean, the Liars uncover clues that suggest "A" is more than one person. They begin to suspect Naomi Zeigler of being "A", after she befriends Hanna (who is unaware that Madison is Naomi's cousin) and attempts to sabotage Spencer's new relationship. Aria becomes friends with a boy named Graham, only to discover he is Tabitha's ex-boyfriend, leading the Liars come to believe that Naomi and Graham are working together as "A". Meanwhile, Emily falls for a stowaway, Jordan, unaware that she is a thief on the run from the authorities.
After an explosion on the boat, the Liars go off on their own to bury "evidence" of their connection to Tabitha (Tabitha's locket, which "A" had planted for Noel to find). "A" tampers with their lifeboat, nearly stranding them in the middle of the ocean. The near-death experience pushes the girls into wanting to confess about killing Tabitha. However, as they make plans to come clean about everything, they discover that they were not responsible for Tabitha's death at all: She had been bludgeoned to death by "A".
The Liars finally come to believe that "A" is, in fact, Alison, as Emily reveals that she may have helped Alison escape the burning Poconos house in Wanted. Suspiciously though Naomi was at Gayle's funeral.

text: Fourth Arc[edit]

text:
Book #

Title

Publication Date

ISBN

Pages

13
Crushed
June 4, 2013
978-0-06-219971-3
340

Weeks before the annual Rosewood Day Prom, the four girls are put under much stress. They break down and try being one step ahead of "A", and marking off who their suspects could be. In this novel it is revealed there are two people working as A. Spencer, Hanna, and Emily agree that the main suspect is Noel Kahn, Aria's boyfriend. Aria doesn't want to believe it but the facts tell her otherwise. He was on the trip to Jamaica, he went to Iceland. He was good friends with Ali (he loved her), and he visited her in the Preserve when she was there. He knew about the twins. He knew enough to make him look like A. Emily tries getting information of out of Ali's old friends, Iris, (who we met in ''Heartless). Iris tells Emily little tidbits of Ali, and at Prom Iris recognizes Noel and for sure he was Ali's secret boyfriend who visited her. Spencer finds an internet blogger, who blogs about Alison DiLaurentis theories. She meets him and actually ends up liking him, finding his name is Chase. He helps Spencer get information on Alison. Hanna, in an attempt to get information on a burned victim from the last book, Graham, starts volunteering at the Burn Clinic. There, Graham is still in a coma and right when he's about to wake up, he dies -all the information is kept hidden for good. Aria, worried and paranoid about what happened last summer, is trying to handle things with Noel being A, even though she doesn't want to believe it. At Prom, Noel admits to loving Ali, and Aria, furious, freaks out and asks Noel if Ali is still alive. He says he doesn't know. While Aria is attempting to get away, Noel pins her to the ground. Spencer, Hanna, and Emily arrive and Noel flees. The morning later, Hanna gets a text from A saying to go to the shed in the Rosewood Day back. She and the three other girls go, and just in case bring Cops and police and inside is a supposedly unconscious Noel tied up to a chair. It is not revealed if Noel is dead or alive. The girls get a text, signed by A, informing them that they've failed to make progress, Noel wasn't A, and they are back where they started.

14
Deadly
December 3, 2013[5]
978-0-06-219974-4
320

The book starts out as the real Alison DiLaurentis is limping out of the burning house in her vacation home right after she tried to kill the liars. It's seemingly said in the start that she survived by the help of "Helper A" her boyfriend. Aria visits Noel in the hospital and it is shown that he is in fact still alive. Agent Fuji comes to the girls after they are arrested for the charges they have committed over the past year. The girls finally admit to Agent Fuji about "A" and told her that all of their charges had to be dropped. They also told her that they thought that Alison was still alive and that they needed 24-hour protection of their family. Agent Fuji tells the girls to give her all of the "A" notes and the girls do as they are told. As a result of telling the police, "A" gave the police a fake security video of the girls beating up Tabitha before she is killed. The police arrest all of them and told the girls that all of the texts from "A" had come from their phones. The girls are put on bail and go home. Emily's family seem to hate her and Emily and Carolyn get into a fight. As this happens Emily's mom has a heart attack. Hanna's father wants nothing to do with her because it will hurt the campaign. After their hearing they are sentenced to go to trial in Jamaica the next day. Certain to find "A" they go searching. They find a house by Hanna's fathers office and go inside. It is small and disgusting. As they are walking in Nick Maxwell comes in pointing a gun at the girls. He is "Helper A" Real Ali's boyfriend. The girls all know him as someone else. Spencer knows him as Phineas, a guy at Penn's summer program who sold her study drugs. Hanna knew him as Jackson, the bartender who kept on giving Madison drinks and refusing to get a cab, resulting in Hanna getting in a wreck with Madison. Emily knew him as Derrick, a friend she had at her job, telling him all of her secrets. And Aria knew him as Olaf, a guy she stole The Starry Night with while vacationing in Iceland. Right as they realized what was happening Alison shows up with a gun and tells the girls to get in the basement. They girls do as they are told and the go down. They see a mural of Ali on the wall and they are confused. Ali tells them that after she kills them that it is going to look like they did it to be with Ali because they were sad that she was gone. Astonished the girls ask questions. After, Nick and Ali grab gas masks and turn on a poisonous gas. They girls awake in the hospital and Agent Fuji tells them that Nick Maxwell was caught but not Ali. In the epilogue Ali is running away and goes to a little house that Nick didn't know of. She has money and reveals that she is going to lure someone else to kill with her again.

15
Toxic
June 3, 2014[6]
9780062287014
336

With A apparently arrested, the girls attempt to move on with their lives. Hanna gets a film offer, and Spencer starts an anti-bullying campaign. However, it is soon revealed that the real A is still seeking vengeance.

16
Vicious
December 2, 2014[7]
9780062287045

After being falsely accused of killing Alison, the girls seek to outwit her and avoid jail time.

text: Companion novels[edit]

text:
Book #

Title

Publication Date

ISBN

Pages

0.6
Alison's Pretty Little Diary
September 6, 2010
978-0-06-223336-3
14

Ali changed the lives of The Liars forever. But now thanks to this diary never seen before, you finally know what Alison was thinking in the day she picked those four girls to be her new best friends.

4.5
Pretty Little Secrets
January 3, 2012
978-0-06-212591-0
464

Set between Unbelievable and Wicked, the book is told from the point of view of the second "A", Alison DiLaurentis, as she spies on the girls during their Christmas vacation. The novel is divided into a series of four short stories, with each one focusing on the exploits of a specific girl.
Spencer: Spencer and her family go to Nana Hastings mansion in Florida, and Spencer falls in love with a tennis player named Colin at the country club. Melissa seems to be helping Spencer win Colin's heart, but Colin ends up taking an interest in Melissa. During the trip, Spencer and her mother also run into Mrs. DiLaurentis several times, and Spencer is confused by her mother's strange behavior around Mrs DiLaurentis. Spencer also decides to fight for Colin. After Colin dumps Melissa to go out with her, Spencer and Melissa discover that Colin's actually 33 years old and also has a wife and child. Spencer and Melissa decide to team up to get revenge on Colin by putting crushed Viagra in his Aminospa vitamin water right before his important tennis game. In the end, they all have a fun vacation, but Spencer worries that someone has been following her. Melissa and Spencer seem to briefly make up in this, hence the sisters' wary friendship in Wicked.
Emily: Emily is asked to go undercover as Santa Claus at the new mall, in order to catch 4 girls who work as elves there, who are suspected of vandalizing Christmas decorations around town, including Emily's mom's baby Jesus ceramic figure. The 4 girls, who call themselves the "Merry Elves", take a liking to Emily, and it's revealed that one of the girls, Cassie, was close with Alison. Emily accompanies the girls on their biggest prank yet, but Emily's mom uses her phone to track her, and the Merry Elves get caught. Eventually, the elves forgive Emily after she bails them out of jail. In the end, everyone realizes the true meaning of Christmas, but Emily can't shake off the weird feeling that someone is following her. It is revealed that A is blonde (she will later be revealed as Alison) as Emily sees a blonde figure run off.
Hanna: Hanna joins a boot camp after thinking she gained too much weight at a holiday party. She develops feelings for the instructor, Vince. She also develops a rival, Dinah, another girl who also likes Vince. After competing for Vince's affection, she and Dinah become friends after catching Kate making out with the mall's new Santa (prior to Emily), something which Hanna also photographs. After agreeing to stop chasing Vince, she celebrates by going out for drinks with Dinah, where Dinah admits she knew Alison. Hanna goes home drunk, causing her to oversleep. As she arrives at boot camp, she discovers Vince and Dinah kissing, revealing that Dinah only pretended to be friends with Hanna to have Hanna let down her guard. Hanna flees the scene, devastated, and is confronted by Kate, who, after receiving a tip-off, followed Hanna around, taking unflattering photos of her at boot camp, which she threatens to put on Facebook. Hanna counterattacks by showing Kate the pictures of her and Santa, causing Kate to back off. Hanna also improves her relationship with her father, who gives Hanna her grandmother's Cartier locket for Christmas/Hanukkah. Hanna has a happy Christmas/Hanukkah, despite the fact that she thinks someone other than Kate has been watching her every move. Some of what Dinah said may be true such as she knew Alison. But it is likely she made most of it up to get Hanna's trust.
Aria: Aria goes with her father and Mike to Bear Claw Resort, but leaves to go back home after finding out that Byron invited Meredith along as well. Upon arriving at home, Aria's surprised to see Halbjorn, an old boyfriend of hers from Iceland. Halbjorn tells her that he's running from the Icelandic police who're after him because he protested against the demolition of a puffin sanctuary. Unfortunately, his travel visa only lasts for a week. Aria proposes the idea of marrying him, and the two head off to Atlantic City to elope. At the hotel, they attend a magic show involving two panthers, which greatly angers Halbjorn, who cares a lot about the environment. After getting married the following day, which requires Aria to forge her mother's signature and lie about her age, they go to the place where the panthers are kept. After convincing Halbjorn not to release the panthers, they go back to the hotel. The next morning, Aria wakes up to find Halbjorn gone and his clothes missing as well. On the lobby's TV, Aria sees that Halbjorn ended up releasing the panthers anyway. Aria goes to the courthouse and confesses to lying about her age and forging her mother's signature, making the marriage null and void. Upon returning to Rosewood, she is joined by Mike and Byron, who know nothing about her marriage. As they watch TV, it shows that Halbjorn has been caught, and it also reveals that he's done these sorts of things in the past, including trying to blow up a demolition office. Aria's satisfied with breaking up with him, but is paranoid about someone following her. In Wicked, it's briefly stated that Aria and Meredith did converse about the baby.
The book ends with a sign-off from the new "A," (as always) who says that the Liars' lives are going to get a lot worse. All of which comes true...

0.5
Ali’s Pretty Little Lies
January 2, 2013
978-0062233363
304

Before there was "A," there was "Alison DiLaurentis". Boys wanted to date her, girls wanted to be her and somebody wanted her dead.
It's the end of seventh grade, and "Alison DiLaurentis" and her friends are the alpha girls of Rosewood Day. "Ali" runs her clique with an iron fist, and she's got enough dirt on Hanna, Emily, Aria and Spencer to keep them in line. But "Ali's" hiding a dark secret of her own, something so huge it would destroy everything if it ever got out. She's desperate to keep the perfect life she's worked so hard to build, but in Rosewood deadly secrets have deadly consequences.
Set in the weeks leading up to "Ali's" murder, this special Pretty Little Liars tale is told by the prettiest little liar of all: "Ali" herself. For the first time ever, we see how the mystery began—and how "Alison DiLaurentis'" life ended.
Note: This book is titled Ali's Pretty Little Lies but it's actually about her twin sister, Courtney, who pretended to be Alison because she didn't want to go to a psych ward. This book reveals a lot of secrets.


document_title: World energy consumption

question_text: how much of the worlds energy is produced by nuclear power

question_tokens: how much of the worlds energy is produced by nuclear power

root

text: World energy consumption

text: Overview[edit]

text: Energy supply, consumption and electricity[edit]

text:
Key figures (TWh)

Year

Primary energysupply (TPES)1

Final energyconsumption1

Electricitygeneration

Ref

1973

71,013(Mtoe 6,106)

54,335(Mtoe 4,672)

6,129

[3]

1990

102,569

–

11,821

–

2000

117,687

–

15,395

–

2010

147,899(Mtoe 12,717)

100,914(Mtoe 8,677)

21,431

[6]

2011

152,504(Mtoe 13,113)

103,716(Mtoe 8,918)

22,126

[7]

2012

155,505(Mtoe 13,371)

104,426(Mtoe 8,979)

22,668

[8]

2013

157,482(Mtoe 13,541)

108,171(Mtoe 9,301)

23,322

[9]

2014

155,481(Mtoe 13,369)

109,613(Mtoe 9,425)

23,816

[10]

2015

168,519(Mtoe 13,647)

[11][12]

1 converted from Mtoe into TWh (1 Mtoe = 11.63 TWh) and from Quad BTU into TWh (1 Quad BTU = 293.07 TWh)

tag: table

text: World total primary energy supply (TPES), or "primary energy" differs from the world final energy consumption because much of the energy that is acquired by humans is lost as other forms of energy during the process of its refinement into usable forms of energy and its transport from its initial place of supply to consumers. For instance, when oil is extracted from the ground it must be refined into gasoline, so that it can be used in a car, and transported over long distances to gas stations where it can be used by consumers. World final energy consumption refers to the fraction of the world's primary energy that is used in its final form by humanity.

tag: p

text: In 2014, world primary energy supply amounted to 155,481 terawatt-hour (TWh) or 13,541 Mtoe, while the world final energy consumption was 109,613 TWh or about 29.5% less than the total supply.[10] World final energy consumption includes products as lubricants, asphalt and petrochemicals which have chemical energy content but are not used as fuel. This non-energy use amounted to 9,404 TWh (809 Mtoe) in 2012.[13]

text: 2014 World electricity generation (23,816 TWh) by source (IEA, 2016)[14]

text: The United States Energy Information Administration (EIA) regularly publishes a report on world consumption for most types of primary energy resources. For 2013, estimated world energy consumption was 5.67 × 1020 joules, or 157,481 TWh. According to the IEA the total world energy consumption in past years was 143,851 TWh in 2008, 133,602 TWh in 2005, 117,687 TWh in 2000, and 102,569 TWh in 1990.[3] In 2012 approximately 22% of world energy was consumed in North America, 5% was consumed South and Central America, 23% was consumed in Europe and Eurasia, 3% was consumed in Africa, and 40% was consumed in the Asia Pacific region.[1]

text: Electricity generation[edit]

text:
The total amount of electricity consumed worldwide was 19,504 TWh in 2013, 16,503 TWh in 2008, 15,105 TWh in 2005, and 12,116 TWh in 2000.
By the end of 2014, the total installed electricity generating capacity worldwide was nearly 6.142 TW (million MW) which only includes generation connected to local electricity grids.[15]
In addition there is an unknown amount of heat and electricity consumed off-grid by isolated villages and industries.
In 2014, the share of world energy consumption for electricity generation by source was coal at 40.8%, natural gas at 21.6%, nuclear at 10.6%, hydro at 16.4%, other sources (solar, wind, geothermal, biomass, etc.) at 6.3% and oil at 4.3%.
Coal and natural gas were the most used energy fuels for generating electricity.
The world's electricity consumption was 18,608 TWh[citation needed] in 2012.
This figure is about 18% smaller than the generated electricity, due to grid losses, storage losses, and self-consumption from power plants (gross generation).
Cogeneration (CHP) power stations use some of the heat that is otherwise wasted for use in buildings or in industrial processes.

text: In 2016 while total world energy came from 80% fossil fuels, 10% biofuels, 5% nuclear and 5% renewable (hydro, wind, solar, geothermal), only 18% of that total world energy was in the form of electricity.[16] Most of the other 82% was used for heat and transportation.

text: Recently there has been a large increase in international agreements and national Energy Action Plans, such as the EU 2009 Renewable Energy Directive, to increase the use of renewable energy due to the growing concerns about pollution from energy sources that come from fossil fuels such as oil, coal, and natural gas.[4][17] One such initiative was the United Nations Development Programme's World Energy Assessment in 2000 that highlighted many challenges humanity would have to overcome in order to shift from fossil fuels to renewable energy sources.[4] From 2000–2012 renewable energy grew at a rate higher than any other point in history, with a consumption increase of 176.5 million tonnes of oil. During this period, oil, coal, and natural gas continued to grow and had increases that were much higher than the increase in renewable energy. The following figures illustrate the growth in consumption of fossil fuels such as oil, coal, and natural gas as well as renewable sources of energy during this period.[1]

text: Trends[edit]

text: The energy consumption growth in the G20 slowed down to 2% in 2011, after the strong increase of 2010. The economic crisis is largely responsible for this slow growth. For several years now, the world energy demand is characterized by the bullish Chinese and Indian markets, while developed countries struggle with stagnant economies, high oil prices, resulting in stable or decreasing energy consumption.[21]

text: According to IEA data from 1990 to 2008, the average energy use per person increased 10% while world population increased 27%. Regional energy use also grew from 1990 to 2008: the Middle East increased by 170%, China by 146%, India by 91%, Africa by 70%, Latin America by 66%, the USA by 20%, the EU-27 block by 7%, and world overall grew by 39%.

text: In 2008, total worldwide primary energy consumption was 132,000 terawatt-hours (TWh) or 474 exajoules (EJ).[22] In 2012, primary energy demand increased to 158,000 TWh (567 EJ).[23]

text: Energy consumption in the G20 increased by more than 5% in 2010 after a slight decline of 2009. In 2009, world energy consumption decreased for the first time in 30 years by 1.1%, or about 130 million tonnes of oil equivalent (Mtoe), as a result of the financial and economic crisis, which reduced world GDP by 0.6% in 2009.[24]

text: This evolution is the result of two contrasting trends: Energy consumption growth remained vigorous in several developing countries, specifically in Asia (+4%). Conversely, in OECD, consumption was severely cut by 4.7% in 2009 and was thus almost down to its 2000 levels. In North America, Europe and the CIS, consumptions shrank by 4.5%, 5% and 8.5% respectively due to the slowdown in economic activity. China became the world's largest energy consumer (18% of the total) since its consumption surged by 8% during 2009 (up from 4% in 2008). Oil remained the largest energy source (33%) despite the fact that its share has been decreasing over time. Coal posted a growing role in the world's energy consumption: in 2009, it accounted for 27% of the total.

text: Most energy is used in the country of origin, since it is cheaper to transport final products than raw materials. In 2008, the share export of the total energy production by fuel was: oil 50% (1,952/3,941 Mt), gas 25% (800/3,149 bcm) and hard coal 14% (793/5,845 Mt).[25]

text: Most of the world's high energy resources are from the conversion of the sun's rays to other energy forms after being incident upon the planet. Some of that energy has been preserved as fossil energy, some is directly or indirectly usable; for example, via solar PV/thermal, wind, hydro- or wave power. The total solar irradiance is measured by satellite to be roughly 1361 watts per square meter (see solar constant), though it fluctuates by about 6.9% during the year due to the Earth's varying distance from the sun. This value, after multiplication by the cross-sectional area intercepted by the Earth, is the total rate of solar energy received by the planet; about half, 89,000 TW, reaches the Earth's surface.[26]

text: The estimates of remaining non-renewable worldwide energy resources vary, with the remaining fossil fuels totaling an estimated 0.4  yottajoule (YJ) or 4 × 1023 joules, and the available nuclear fuel such as uranium exceeding 2.5 YJ. Fossil fuels range from 0.6 to 3 YJ if estimates of reserves of methane clathrates are accurate and become technically extractable. The total power flux from the sun intercepting the Earth is 5.5 YJ per year, though not all of this is available for human consumption. The IEA estimates for the world to meet global energy demand for the two decades from 2015 to 2035 it will require investment of $48 trillion and "credible policy frameworks."[27]

text: According to IEA (2012) the goal of limiting warming to 2 °C is becoming more difficult and costly with each year that passes. If action is not taken before 2017, CO2 emissions would be locked-in by energy infrastructure existing in 2017. Fossil fuels are dominant in the global energy mix, supported by $523 billion subsidies in 2011, up almost 30% on 2010 and six times more than subsidies to renewables.[28]

text:
Regional energy use (kWh/capita & TWh) and growth 1990–2008 (%)[29][30]

kWh/capita

Population (million)

Energy use (1,000 TWh)

Region

1990

2008

Growth

1990

2008

Growth

1990

2008

Growth

USA

89,021
87,216
−2%

250
305
22%

22.3
26.6
20%

EU-28

40,240
40,821
1%

473
499
5%

19.0
20.4
7%

Middle East

19,422
34,774
79%

132
199
51%

2.6
6.9
170%

China

8,839
18,608
111%

1,141
1,333
17%

10.1
24.8
146%

Latin America

11,281
14,421
28%

355
462
30%

4.0
6.7
66%

Africa

7,094
7,792
10%

634
984
55%

4.5
7.7
70%

India

4,419
6,280
42%

850
1,140
34%

3.8
7.2
91%

Others*

25,217
23,871
nd

1,430
1,766
23%

36.1
42.2
17%

The World

19,422
21,283
10%

5,265
6,688
27%

102.3
142.3
39%

Source: IEA/OECD, Population OECD/World Bank
Energy use = kWh/capita * billion capita (population) = 1 TWh
Others: Mathematically calculated, includes e.g. countries in Asia and Australia. The use of energy varies between the "other countries": E.g. in Australia, Japan, or Canada energy is used more per capita than in Bangladesh or Burma.

text: Emissions[edit]

text: Global warming emissions resulting from energy production are an environmental problem. Efforts to resolve this include the Kyoto Protocol, which is a UN agreement aiming to reduce harmful climate impacts, which a number of nations have signed. Limiting global temperature increase to 2 degrees Celsius, thought to be a risk by the SEI, is now doubtful.

text: To limit global temperature to a hypothetical 2 degrees Celsius rise would demand a 75% decline in carbon emissions in industrial countries by 2050, if the population is 10 billion in 2050.[31] Across 40 years, this averages to a 2% decrease every year. In 2011, the emissions of energy production continued rising regardless of the consensus of the basic problem. Hypothetically, according to Robert Engelman (Worldwatch institute), in order to prevent collapse, human civilization would have to stop increasing emissions within a decade regardless of the economy or population (2009).[32]

text: Greenhouse gases are not the only emissions of energy production and consumption. Large amounts of pollutants such as sulphurous oxides (SOx), nitrous oxides (NOx), and particulate matter (PM) are produced from the combustion of fossil fuels and biomass; the World Health Organisation estimates that 7 million premature deaths are caused each year by air pollution.[33] Biomass combustion is a major contributor.[33][34][35] In addition to producing air pollution like fossil fuel combustion, most biomass has high CO2 emissions.[36]

text: By source[edit]

text: Total primary energy supply of  13,699 mega-toe by source in 2014 (IEA, 2016)[14][8]:28

text: Fossil fuels[edit]

text: The twentieth century saw a rapid twenty-fold increase in the use of fossil fuels. Between 1980 and 2006, the worldwide annual growth rate was 2%.[22] According to the US Energy Information Administration's 2006 estimate, the estimated 471.8 EJ total consumption in 2004, was divided as given in the table above, with fossil fuels supplying 86% of the world's energy:

text: Coal[edit]

text: In 2000, China accounted for 28% of world coal consumption, other Asia consumed 19%, North America 25% and the EU 14%. The single greatest coal-consuming country is China. Its share of the world coal production was 28% in 2000 and rose to 48% in 2009. In contrast to China's ~70% increase in coal consumption, world coal use increased 48% from 2000 to 2009. In practice, the majority of this growth occurred in China and the rest in other Asia.[37] China's energy consumption is mostly driven by the industry sector, the majority of which comes from coal consumption.[38]

text: World annual coal production increased 1,905 Mt or 32% in 6 years in 2011 compared to 2005, of which over 70% was in China and 8% in India. Coal production was in 2011 7,783 Mt, and 2009 6,903 Mt, equal to 12.7% production increase in two years.[39]

text: If production and consumption of coal continue at the rate as in 2008, proven and economically recoverable world reserves of coal would last for about 150 years. This is much more than needed for an irreversible climate catastrophe. Coal is the largest source of carbon dioxide emissions in the world. According to James Hansen the single most important action needed to tackle the climate crisis is to reduce CO2 emissions from coal.[40] Indonesia and Australia exported together 57.1% of the world coal export in 2011. China, Japan, South Korea, India and Taiwan had 65% share of all the world coal import in 2011.[41]

text:
Regional coal supply (TWh), share 2010 (%) and share of change 2000–2010[37][42]

Region

2000

2008

2009*

2010*

%*

Change2000–2009*

North America

6,654
6,740
6,375
6,470
16%
−1.2%

Asia excl. China

5,013
7,485
7,370
7,806
19%
18.9%

China

7,318
16,437
18,449
19,928
48%
85.5%

EU

3,700
3,499
3,135
3,137
8%
−3.8%

Africa

1,049
1,213
1,288
1,109
3%
0.4%

Russia

1,387
1,359
994
1,091
3%
−2.0%

Others

1,485
1,763
1,727
1,812
4%
2.2%

Total

26,607
38,497
39,340
41,354
100%
47.9%

Source: IEA, *in 2009, 2010 BP*Change 2000–2009: Region's share of the world change +12,733 TWh from 2000 to 2009

text:
Top 10 coal exporters (Mt)[43]

Rank

Nation

2010

2011

Share% 2011

2012

1

Indonesia

162
309
29.7%
383

2

Australia

298
285
27.4%
302

3

Russia

89
99
9.5%
103

4

US

57
85
8.2%
106

5

Colombia

68
76
7.3%
82

6

South Africa

68
70
6.7%
72

7

Kazakhstan

33
34
3.3%
32

8

Canada

24
24
2.3%
25

9

Vietnam

21
23
2.2%
18

10

Mongolia

17
22
2.1%
22

x

Others

19
14
1.3%

Total (Mt)

856
1,041

1,168

Top ten

97.8%
98.7%

text: Oil[edit]

text: Coal fueled the industrial revolution in the 18th and 19th century. With the advent of the automobile, aeroplanes and the spreading use of electricity, oil became the dominant fuel during the twentieth century. The growth of oil as the largest fossil fuel was further enabled by steadily dropping prices from 1920 until 1973. After the oil shocks of 1973 and 1979, during which the price of oil increased from 5 to 45 US dollars per barrel, there was a shift away from oil.[44] Coal, natural gas, and nuclear became the fuels of choice for electricity generation and conservation measures increased energy efficiency. In the U.S. the average car more than doubled the number of miles per gallon. Japan, which bore the brunt of the oil shocks, made spectacular improvements and now has the highest energy efficiency in the world.[45] From 1965 to 2008, the use of fossil fuels has continued to grow and their share of the energy supply has increased. From 2003 to 2008, coal was the fastest growing fossil fuel.[46]

text: It is estimated that between 100 and 135 billion tonnes of oil has been consumed between 1850 and the present.[47]

text: Natural Gas[edit]

text: In 2009, the world use of natural gas grew 31% compared to 2000. 66% of this growth was outside EU, North America, Latin America, and Russia. Others include the Middle East, Asia, and Africa. The gas supply increased also in the previous regions: 8.6% in the EU and 16% in the North America 2000–2009.[48]

text:
Regional gas supply (TWh) and share 2010 (%)[42][48]

Land

2000

2008

2009

2010

%

North America

7,621
7,779
8,839
8,925
27%

Asia excl. China

2,744
4,074
4,348
4,799
14%

China

270
825
1,015
1,141
3%

EU

4,574
5,107
4,967
5,155
16%

Africa

612
974
1,455
1,099
3%

Russia

3,709
4,259
4,209
4,335
13%

Latin America

1,008
1,357
958
nd
nd

Others

3,774
5,745
6,047
7,785
23%

Total
24,312
30,134
31,837
33,240
100%

Source: IEA, in 2009, 2010 BP

text: Nuclear power[edit]

text: As of 1 July 2016, the world had 444 operable grid-electric nuclear power reactors with 62 others under construction.[49] Since commercial nuclear energy began in the mid 1950s, 2008 was the first year that no new nuclear power plant was connected to the grid, although two were connected in 2009.[50][51]

text: Annual generation of nuclear power has been on a slight downward trend since 2007, decreasing 1.8% in 2009 to 2558 TWh, and another 1.6% in 2011 to 2518 TWh, despite increases in production from most countries worldwide, because those increases were more than offset by decreases in Germany and Japan. Nuclear power met 11.7% of the world's electricity demand in 2011. Source: IEA/OECD[7]

text: Renewable energy[edit]

text: Renewable energy is generally defined as energy that comes from resources that are not significantly depleted by their use, such as sunlight, wind, rain, tides, waves and geothermal heat.[53] Renewable energy is gradually replacing conventional fuels in four distinct areas: electricity generation, hot water/space heating, motor fuels, and rural (off-grid) energy services.[54]

text: Based on REN21's 2014 report, renewables contributed 19 percent to our energy consumption and 22 percent to our electricity generation in 2012 and 2013, respectively. This energy consumption is divided as 9% coming from traditional biomass, 4.2% as heat energy (non-biomass), 3.8% hydro electricity and 2% electricity from wind, solar, geothermal, and biomass. Worldwide investments in renewable technologies amounted to more than US$214 billion in 2013, with countries like China and the United States heavily investing in wind, hydro, solar and biofuels.[55] Renewable energy resources exist over wide geographical areas, in contrast to other energy sources, which are concentrated in a limited number of countries. Rapid deployment of renewable energy and energy efficiency is resulting in significant energy security, climate change mitigation, and economic benefits.[56] In international public opinion surveys there is strong support for promoting renewable sources such as solar power and wind power.[57] At the national level, at least 30 nations around the world already have renewable energy contributing more than 20 percent of energy supply. National renewable energy markets are projected to continue to grow strongly in the coming decade and beyond.[58]

text: The following table shows increasing nameplate capacity, and has capacity factors that range from 11% for solar, to 40% for hydropower.[59]

text:
Selected renewable energy global indicators
2008
2009
2010
2011
2012
2013
2014
2015

Investment in new renewable capacity (annual) (109 USD)[60]
182
178
237
279
256
232
270
285

Renewables power capacity (existing) (GWe)
1,140
1,230
1,320
1,360
1,470
1,578
1,712
1,849

Hydropower capacity (existing) (GWe)
885
915
945
970
990
1,018
1,055
1,064

Wind power capacity (existing) (GWe)
121
159
198
238
283
319
370
433

Solar PV capacity (grid-connected) (GWe)
16
23
40
70
100
138
177
227

Solar hot water capacity (existing) (GWth)
130
160
185
232
255
373
406
435

Ethanol production (annual) (109 litres)
67
76
86
86
83
87
94
98

Biodiesel production (annual) (109 litres)
12
17.8
18.5
21.4
22.5
26
29.7
30

Countries with policy targets  for renewable energy use
79
89
98
118
138
144
164
173

Source: The Renewable Energy Policy Network for the 21st Century (REN21)–Global Status Report[61][62][63][64][65]

text:
Renewable energy 2000-2013 (TWh)[66]

2000

2010

2013

North-America
1,973
2,237
2,443

EU
1,204
2,093
2,428

Russia
245
239
271

China
2,613
3,374
3,847

Asia (-China)
4,147
4,996
5,361

Africa
2,966
3,930
4,304

Latin America
1 502
2,127
2,242

Other
567
670
738

Total renewable
15,237
19,711
21,685

Total energy
116,958
148,736
157,485

Share
13.0%
13.3%
13.8%

Total nonrenewable
101,721
129,025
135,800

text: From 2000 to 2013 the total renewable energy use has increased 6,450 TWh and total energy use 40,500 TWh.

text: Hydro[edit]

text: Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the kinetic energy of falling or flowing water. In 2015 hydropower generated 16.6% of the world's total electricity and 70% of all renewable electricity,[67] which continues the rapid rate of increase experienced between 2003 and 2009.[68] Hydropower is produced in 150 countries, with the Asia-Pacific region generating 32 percent of global hydropower in 2010. China is the largest hydroelectricity producer, with 2,600 PJ (721 TWh) of production in 2010, representing around 17% of domestic electricity use. There are now three hydroelectricity plants larger than 10 GW: the Three Gorges Dam in China, Itaipu Dam in Brazil, and Guri Dam in Venezuela.[68] Nine of the worlds top 10 renewable electricity producers are primarily hydroelectric, one is wind.

text: Marine energy[edit]

text: Marine energy, also known as ocean energy and marine and hydrokinetic energy (MHK) includes tidal and wave power and is a relatively new sector of renewable energy, with most projects still in the pilot phase, but the theoretical potential is equivalent to 4–18 million tonne of oil equivalent (toe). MHK development in U.S. and international waters includes projects using devices such as, wave energy converters in open coastal areas with significant waves, tidal turbines placed in coastal and estuarine areas, in-stream turbines in fast-moving rivers, ocean current turbines in areas of strong marine currents, and ocean thermal energy converters in deep tropical waters.[69]

text: Wind[edit]

text: Wind power is growing at the rate of 17% annually, with a worldwide installed capacity of 432,883 megawatts (MW) at the end of 2015,[70][71][72] and is widely used in Europe, Asia, and the United States.[73][74] Several countries have achieved relatively high levels of wind power penetration, such as 21% of stationary electricity production in Denmark,[75] 18% in Portugal,[75] 16% in Spain,[75] 14% in Ireland[76] and 9% in Germany in 2010.[75][77] As of 2011, 83 countries around the world are using wind power on a commercial basis.[77] Continuing strong growth, by 2016 wind generated 3% of global power annually.[78]

text: Solar[edit]

text: Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar energy technologies include solar heating, solar photovoltaics, concentrated solar power and solar architecture, which can make considerable contributions to solving some of the most urgent problems the world now faces. The International Energy Agency projected that solar power could provide "a third of the global final energy demand after 2060, while CO2 emissions would be reduced to very low levels."[79] Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute solar energy. Active solar techniques include the use of photovoltaic systems and solar thermal collectors to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air. From 2012 to 2016 solar capacity tripled and now provides 1.3% of global energy.[80]

text: Geothermal[edit]

text: Geothermal energy is used commercially in over 70 countries.[81] In 2004, 200 petajoules (56 TWh) of electricity was generated from geothermal resources, and an additional 270 petajoules (75 TWh) of geothermal energy was used directly, mostly for space heating. In 2007, the world had a global capacity for 7010100000000000000♠10 GW of electricity generation and an additional 7010280000000000000♠28 GW of direct heating, including extraction by geothermal heat pumps.[82][83] Heat pumps are small and widely distributed, so estimates of their total capacity are uncertain and range up to 7011100000000000000♠100 GW.[81]

text: Bio energy[edit]

text: Until the beginning of the nineteenth century biomass was the predominant fuel, today it has only a small share of the overall energy supply. Electricity produced from biomass sources was estimated at 44 GW for 2005. Biomass electricity generation increased by over 100% in Germany, Hungary, the Netherlands, Poland, and Spain. A further 220 GW was used for heating (in 2004), bringing the total energy consumed from biomass to around 264 GW. The use of biomass fires for cooking is excluded.[82] World production of bioethanol increased by 8% in 2005 to reach 33 gigalitres (8.7×109 US gal), with most of the increase in the United States, bringing it level to the levels of consumption in Brazil.[82] Biodiesel increased by 85% to 3.9 gigalitres (1.0×109 US gal), making it the fastest growing renewable energy source in 2005. Over 50% is produced in Germany.[82]

text: By country[edit]

text: World total final consumption of 13,699 Mtoe by region in 2014 (IEA, 2016)[14]

text: Energy consumption is loosely correlated with gross national product and climate, but there is a large difference even between the most highly developed countries, such as Japan and Germany with an energy consumption rate of 6 kW per person and the United States with an energy consumption rate of 11.4 kW per person. In developing countries, particularly those that are sub-tropical or tropical such as India, the per person energy use rate is closer to 0.7 kW. Bangladesh has the lowest consumption rate with 0.2 kW per person.

text: The US consumes 25% of the world's energy with a share of global GDP at 22% and a share of the world population at 4.59%.[84] The most significant growth of energy consumption is currently taking place in China, which has been growing at 5.5% per year over the last 25 years. Its population of 1.3 billion people (19.6% of the world population[84]) is consuming energy at a rate of 1.6 kW per person.

text: One measurement of efficiency is energy intensity. This is a measure of the amount of energy it takes a country to produce a dollar of gross domestic product.

text: Oil[edit]

text: Saudi Arabia, Russia and the United States accounted for 34% of oil production in 2011. Saudi Arabia, Russia and Nigeria accounted for 36% of oil export in 2011.

text:
Top 10 oil producers (Mt)[43]

Rank

Nation

2005

2008

2009

2010

2011

Share %2011

2012

1

Saudi Arabia

519
509
452
471
517
12.9%
544

2

Russia

470
485
494
502
510
12.7%
520

3

United States

307
300
320
336
346
8.6%
387

4

Iran

205
214
206
227
215
5.4%
186

5

China

183
190
194
200
203
5.1%
206

6

Canada

143
155
152
159
169
4.2%
182

7

UAE

nd
136
120
129
149
3.7%
163

8

Venezuela

162
137
126
149
148
3.7%
162

9

Mexico

188
159
146
144
144
3.6%
nd

10

Nigeria

133
nd
nd
130
139
3.5%
nd

x

Kuwait

nd
145
124
nd
nd
nd
152

x

Iraq

nd
nd
114
140
nd
nd
148

x

Norway

139
nd
nd
nd
nd
nd
nd

Total

3,923
3,941
3,843
3,973
4,011
100%

Top ten

62%
62%
61%
62%
63%

text:
Top 10 oil exporters (Mt)[85]

Rank

Nation

2011

Share %2011

2012

1

Saudi Arabia

333
17.0%

2

Russia

246
12.5%

3

Nigeria

129
6.6%

4

Iran

126
6.4%

5

UAE

105
5.4%

6

Iraq

94
4.8%

7

Venezuela

87
4.4%

8

Angola

84
4.3%

9

Norway

78
4.0%

10

Mexico

71
3.6%

x

Others

609
31.0%

Total (Mt)

1,962

text: Coal[edit]

text:
Top 10 coal producers (Mt)[43]

Rank

Nation

2005

2008

2009

2010

2011

Share %2011

2012

1

China

2,226
2,761
2,971
3,162
3,576
46%
3,549

2

US

1,028
1,076
985
997
1,004
13%
935

3

India

430
521
561
571
586
8%
595

4

Australia

372
397
399
420
414
5%
421

5

Indonesia

318
284
301
336
376
5%
443

6

Russia

222
323
297
324
334
4%
354

7

South Africa

315
236
247
255
253
3%
259

8

Germany

nd
nd
nd
nd
189
2%
197

9

Poland

160
144
135
134
139
2%
144

10

Kazakhstan

79
108
101
111
117
2%
126

11

Colombia

65
79
73
74
1%
nd
nd

Total

5,878
6,796
6,903
7,229
7,783
100%
7,831

Top ten

89%
87%
88%
88%
nd
90%

*include hard coal and brown coal

text:
Top 10 coal importers (Mt)[86]

Rank

Nation

2005

2008

2009

2010

2011

1

China

25
nd
114
157
177

2

Japan

178
186
165
187
175

3

South Korea

77
100
103
119
129

4

India

37
58
66
88
101

5

Taiwan

61
66
60
63
66

6

Germany

38
46
38
45
41

7

UK

44
43
38
26
32

8

Turkey

nd
19
20
27
24

9

Italy

24
25
19
22
23

10

Malaysia

nd
nd
nd
19
21

x

Spain

25
19
16
nd
nd

x

France

nd
21
nd
nd
nd

x

US

28
nd
nd
nd
nd

Total

778
778
819
949
1,002

Top ten

69%
75%
78%
79%
79%

Import of production

16%
13%
14%
15%
13%

*2005–2010 hard coal

text: Natural gas[edit]

text:
Top 10 natural gas producers (bcm)[85]

Rank

Nation

2005

2008

2009

2010

2011

Share %2011

1

Russia

627
657
589
637
677
20.0%

2

US

517
583
594
613
651
19.2%

3

Canada

187
175
159
160
160
4.7%

4

Qatar

nd
79
89
121
151
4.5%

5

Iran

84
121
144
145
149
4.4%

6

Norway

90
103
106
107
106
3.1%

7

China

nd
76
90
97
103
3.0%

8

Saudi Arabia

70
nd
nd
82
92
2.7%

9

Indonesia

77
77
76
88
92
2.7%

10

Netherlands

79
85
79
89
81
2.4%

x

Algeria

93
82
81
nd
nd
nd

x

UK

93
nd
nd
nd
nd
nd

Total

2,872
3,149
3,101
3,282
100%
3,388

Top ten

67%
65%
65%
65%
67%

bcm = billion cubic meters

text:
Top 10 natural gas importers (bcm)[85]

Rank

Nation

2005

2008

2009

2010

2011

Share %2011

1

Japan

81
95
93
99
116
13.9%

2

Italy

73
77
69
75
70
8.4%

3

Germany

91
79
83
83
68
8.2%

4

US

121
84
76
74
55
6.6%

5

South Korea

29
36
33
43
47
5.6%

6

Ukraine

62
53
38
37
44
5.3%

7

Turkey

27
36
35
37
43
5.2%

8

France

47
44
45
46
41
4.9%

9

UK

nd
26
29
37
37
4.4%

10

Spain

33
39
34
36
34
4.1%

x

Netherlands

23
nd
nd
nd
nd
nd

Total

838
783
749
820
834
100%

Top ten

70%
73%
71%
69%
67%

Import of production

29%
25%
24%
25%
25%

bcm = billion cubic meters

text: Wind power[edit]

text:
Top 10 countriesby nameplate windpower capacity(2011 year-end)[87]

Country

Windpower capacity(MW) ǂprovisional

% world total

China

62,733ǂ
26.3

United States

46,919
19.7

Germany

29,060
12.2

Spain

21,674
9.1

India

16,084
6.7

France

6,800ǂ
2.8

Italy

6,747
2.8

United Kingdom

6,540
2.7

Canada

5,265
2.2

Portugal

4,083
1.7

(rest of world)

32,446
13.8

World total

238,351 MW
100%

text:
Top 10 countriesby windpower electricity production(2010 totals)[88]

Country

Windpower production(TWh)

% world total

United States

95.2
27.6

China

55.5
15.9

Spain

43.7
12.7

Germany

36.5
10.6

India

20.6
6.0

United Kingdom

10.2
3.0

France

9.7
2.8

Portugal

9.1
2.6

Italy

8.4
2.5

Canada

8.0
2.3

(rest of world)

48.5
14.1

World total

344.8 TWh
100%

text: By sector[edit]

text:
World energy use by sector, 2012[89]

Sector

1015Btu

Petawatt-hours

percentage

Residential

53.0
15.5
13

Commercial

29.3
8.6
7

Industrial

222.3
65.1
54

Transportation

104.2
30.5
26

Total*

408.9
119.8
100

Source: US DOE. PWh from 0.293 times Btu column.Numbers are the end use of energy

text: The table to the right shows the amounts of energy consumed worldwide in 2012 by four sectors, according to the Energy Information Administration of the US Department of Energy:

text:
Residential (heating, lighting, and appliances)
Commercial (lighting, heating and cooling of commercial buildings, and provision of water and sewer services)
Industrial users (agriculture, mining, manufacturing, and construction)
Transportation (passenger, freight, and pipeline)

tag: ul

text: Of the total 120 PWh (7020432000000000000♠120×1015 Wh) consumed, 19.4 were in the form of electricity, but this electricity required 61.7 PWh to produce. Thus the total energy consumption was around 160 PWh (ca 7020580280718941000♠550×1015 Btu).[89] The efficiency of a typical existing power plant is around 38%.[90] The new generation of gas-fired plants reaches a substantially higher efficiency of 55%. Coal is the most common fuel for the world's electricity plants.[91]

text: Another report gives different values for the sectors, apparently due to different definitions. According to this, total world energy use per sector in 2008 was industry 28%, transport 27% and residential and service 36%. Division was about the same in the year 2000.[92]

text:
World energy use per sector[92]

Year

2000

2008

2000

2008

Sector

TWh

%*

Industry

21,733
27,273
26.5
27.8

Transport

22,563
26,742
27.5
27.3

Residential and service

30,555
35,319
37.3
36.0

Non-energy use

7,119
8,688
8.7
8.9

Total*

81,970
98,022
100
100

Source: IEA 2010, Total is calculated from the given sectorsNumbers are the end use of energyTotal world energy supply (2008) 143,851 TWh

text: European Union[edit]

text: The European Environmental Agency (EEA) measures final energy consumption (does not include energy used in production and lost in transportation) and finds that the transport sector is responsible for 31.8% of final energy consumption, households 26.2%, industry 25.6%, services 13.5% and agriculture 2.9% in 2012.[93] The use of energy is responsible for the majority of greenhouse gas emissions (79%), with the energy sector representing 31%, transport 19%, industry 13%, households 9% and others 7%.[94]

text: While efficient energy use and resource efficiency are growing as public policy issues, more than 70% of coal plants in the European Union are more than 20 years old and operate at an efficiency level of between 32–40%.[95] Technological developments in the 1990s have allowed efficiencies in the range of 40–45% at newer plants.[95] However, according to an impact assessment by the European Commission, this is still below the best available technological (BAT) efficiency levels of 46–49%.[95] With gas-fired power plants the average efficiency is 52% compared to 58–59% with best available technology (BAT), and gas and oil boiler plants operate at average 36% efficiency (BAT delivers 47%).[95] According to that same impact assessment by the European Commission, raising the efficiency of all new plants and the majority of existing plants, through the setting of authorisation and permit conditions, to an average generation efficiency of 51.5% in 2020 would lead to a reduction in annual consumption of 15 km3 (3.6 cu mi) of natural gas and 25 Mt (25,000,000 long tons; 28,000,000 short tons) of coal.[95]


document_title: Nutrient cycle

question_text: when is a substance considered to be a limiting nutrient

text: Nutrient cycle

text: Outline[edit]

text: The nutrient cycle is nature's recycling system. All forms of recycling have feedback loops that uses energy in the process of putting material resources back into use. Recycling in ecology is regulated to a large extent during the process of decomposition.[2] Ecosystems employ biodiversity in the food webs that recycle natural materials, such as mineral nutrients, which includes water. Recycling in natural systems is one of the many ecosystem services that sustain and contribute to the well-being of human societies.[3][4][5]

text: There is much overlap between the terms for biogeochemical cycle and nutrient cycle. Most textbooks integrate the two and seem to treat them as synonymous terms.[6] However, the terms often appear independently. Nutrient cycle is more often used in direct reference to the idea of an intra-system cycle, where an ecosystem functions as a unit. From a practical point it does not make sense to assess a terrestrial ecosystem by considering the full column of air above it as well as the great depths of Earth below it. While an ecosystem often has no clear boundary, as a working model it is practical to consider the functional community where the bulk of matter and energy transfer occurs.[7] Nutrient cycling occurs in ecosystems that participate in the "larger biogeochemical cycles of the earth through a system of inputs and outputs."[7]:425

text: Complete and closed loop[edit]

text: All systems recycle. The biosphere is a network of continually recycling materials and information in alternating cycles of convergence and divergence. As materials converge or become more concentrated they gain in quality, increasing their potentials to drive useful work in proportion to their concentrations relative to the environment. As their potentials are used, materials diverge, or become more dispersed in the landscape, only to be concentrated again at another time and place.[8]:2

tag: div

text: Ecosystems are capable of complete recycling. Complete recycling means that 100% of the waste material can be reconstituted indefinitely. This idea was captured by Howard T. Odum when he penned that "it is thoroughly demonstrated by ecological systems and geological systems that all the chemical elements and many organic substances can be accumulated by living systems from background crustal or oceanic concentrations without limit as to concentration so long as there is available solar or other source of potential energy"[9]:29 In 1979 Nicholas Georgescu-Roegen proposed a fourth law of entropy stating that complete recycling is impossible. Despite Georgescu-Roegen's extensive intellectual contributions to the science of ecological economics, the fourth law has been rejected in line with observations of ecological recycling.[10][11] However, some authors state that complete recycling is impossible for technological waste.[12]

text: Ecosystems execute closed loop recycling where demand for the nutrients that adds to the growth of biomass exceeds supply within that system. There are regional and spatial differences in the rates of growth and exchange of materials, where some ecosystems may be in nutrient debt (sinks) where others will have extra supply (sources). These differences relate to climate, topography, and geological history leaving behind different sources of parent material.[7][15] In terms of a food web, a cycle or loop is defined as "a directed sequence of one or more links starting from, and ending at, the same species."[16]:185 An example of this is the microbial food web in the ocean, where "bacteria are exploited, and controlled, by protozoa, including heterotrophic microflagellates which are in turn exploited by ciliates. This grazing activity is accompanied by excretion of substances which are in turn used by the bacteria, so that the system more or less operates in a closed circuit."[17]:69–70

text: Ecological recycling[edit]

text: A large fraction of the elements composing living matter reside at any instant of time in the world’s biota. Because the earthly pool of these elements is limited and the rates of exchange among the various components of the biota are extremely fast with respect to geological time, it is quite evident that much of the same material is being incorporated again and again into different biological forms. This observation gives rise to the notion that, on the average, matter (and some amounts of energy) are involved in cycles.[18]:219

text: An example of ecological recycling occurs in the enzymatic digestion of cellulose. "Cellulose, one of the most abundant organic compounds on Earth, is the major polysaccharide in plants where it is part of the cell walls. Cellulose-degrading enzymes participate in the natural, ecological recycling of plant material."[19] Different ecosystems can vary in their recycling rates of litter, which creates a complex feedback on factors such as the competitive dominance of certain plant species. Different rates and patterns of ecological recycling leaves a legacy of environmental effects with implications for the future evolution of ecosystems.[20]

text: Ecological recycling is common in organic farming, where nutrient management is fundamentally different compared to agri-business styles of soil management. Organic farms that employ ecosystem recycling to a greater extent support more species (increased levels of biodiversity) and have a different food web structure.[21][22] Organic agricultural ecosystems rely on the services of biodiversity for the recycling of nutrients through soils instead of relying on the supplementation of synthetic fertilizers.[23][24] The model for ecological recycling agriculture adheres to the following principals:

text:
Protection of biodiversity.
Use of renewable energy.
Recycling of plant nutrients.[25]

text: Ecosystem engineers[edit]

text: The persistent legacy of environmental feedback that is left behind by or as an extension of the ecological actions of organisms is known as niche construction or ecosystem engineering. Many species leave an effect even after their death, such as coral skeletons or the extensive habitat modifications to a wetland by a beaver, whose components are recycled and re-used by descendants and other species living under a different selective regime through the feedback and agency of these legacy effects.[28][29] Ecosystem engineers can influence nutrient cycling efficiency rates through their actions.

text: Earthworms, for example, passively and mechanically alter the nature of soil environments. Bodies of dead worms passively contribute mineral nutrients to the soil. The worms also mechanically modify the physical structure of the soil as they crawl about (bioturbation), digest on the moulds of organic matter they pull from the soil litter. These activities transport nutrients into the mineral layers of soil. Worms discard wastes that create worm castings containing undigested materials where bacteria and other decomposers gain access to the nutrients. The earthworm is employed in this process and the production of the ecosystem depends on their capability to create feedback loops in the recycling process.[30][31]

text: Shellfish are also ecosystem engineers because they: 1) Filter suspended particles from the water column; 2) Remove excess nutrients from coastal bays through denitrification; 3) Serve as natural coastal buffers, absorbing wave energy and reducing erosion from boat wakes, sea level rise and storms; 4) Provide nursery habitat for fish that are valuable to coastal economies.[32]

text: Fungi contribute to nutrient cycling[33] and nutritionally rearrange patches of ecosystem creating niches for other organisms.[34] In that way fungi ingrowing dead wood allow xylophages to grow and develop and xylophages in turn affect dead wood, contributing to wood decomposition and nutrient cycling in the forest floor.[35]

text: History[edit]

text: Nutrient cycling has a historical foothold in the writings of Charles Darwin in reference to the decomposition actions of earthworms. Darwin wrote about "the continued Following the Greeks, the idea of a hydrological cycle (water is considered a nutrient) was validated and quantified by Halley in 1687.

text: Variations in terminology[edit]

text: In 1926 Vernadsky coined the term biogeochemistry as a sub-discipline of geochemistry.[36] However, the term nutrient cycle pre-dates biogeochemistry in a pamphlet on silviculture in 1899: "These demands by no means pass over the fact that at places where sufficient quantities of humus are available and where, in case of continuous decomposition of litter, a stable, nutrient humus is present, considerable quantities of nutrients are also available from the biogenic nutrient cycle for the standing timber.[37]:12 In 1898 there is a reference to the nitrogen cycle in relation to nitrogen fixing microorganisms.[38] Other uses and variations on the terminology relating to the process of nutrient cycling appear throughout history:

text:
The term mineral cycle appears early in a 1935 in reference to the importance of minerals in plant physiology: "...ash is probably either built up into its permanent structure, or deposited in some way as waste in the cells, and so may not be free to re-enter the mineral cycle."[39]:301
The term nutrient recycling appears in a 1964 paper on the food ecology of the wood stork: "While the periodic drying up and reflooding of the marshes creates special survival problems for organisms in the community, the fluctuating water levels favor rapid nutrient recycling and subsequent high rates of primary and secondary production"[40]:97
The term natural cycling appears in a 1968 paper on the transportation of leaf litter and its chemical elements for consideration in fisheries management: "Fluvial transport of tree litter from drainage basins is a factor in natural cycling of chemical elements and in degradation of the land."[41]:131
The term ecological recycling appears in a 1968 publication on future applications of ecology for the creation of different modules designed for living in extreme environments, such as space or under sea: "For our basic requirement of recycling vital resources, the oceans provide much more frequent ecological recycling than the land area. Fish and other organic populations have higher growth rates, vegetation has less capricious weather problems for sea harvesting."[42]
The term bio-recycling appears in a 1976 paper on the recycling of organic carbon in oceans: "Following the actualistic assumption, then, that biological activity is responsible for the source of dissolved organic material in the oceans, but is not important for its activities after death of the organisms and subsequent chemical changes which prevent its bio-recycling, we can see no major difference in the behavior of dissolved organic matter between the prebiotic and post-biotic oceans."[43]:414

text: Water is also a nutrient.[44] In this context, some authors also refer to precipitation recycling, which "is the contribution of evaporation within a region to precipitation in that same region."[45] These variations on the theme of nutrient cycling continue to be used and all refer to processes that are part of the global biogeochemical cycles. However, authors tend to refer to natural, organic, ecological, or bio-recycling in reference to the work of nature, such as it is used in organic farming or ecological agricultural systems.[25]

text: Recycling in novel ecosystems[edit]

text: An endless stream of technological waste accumulates in different spatial configurations across the planet and turns into a predator in our soils, our streams, and our oceans.[46][47] This idea was similarly expressed in 1954 by ecologist Paul Sears: "We do not know whether to cherish the forest as a source of essential raw materials and other benefits or to remove it for the space it occupies. We expect a river to serve as both vein and artery carrying away waste but bringing usable material in the same channel. Nature long ago discarded the nonsense of carrying poisonous wastes and nutrients in the same vessels."[48]:960 Ecologists use population ecology to model contaminants as competitors or predators.[49] Rachel Carson was an ecological pioneer in this area as her book Silent Spring inspired research into biomagification and brought to the worlds attention the unseen pollutants moving into the food chains of the planet.[50]

text: In contrast to the planets natural ecosystems, technology (or technoecosystems) is not reducing its impact on planetary resources.[51][52] Only 7% of total plastic waste (adding up to millions upon millions of tons) is being recycled by industrial systems; the 93% that never makes it into the industrial recycling stream is presumably absorbed by natural recycling systems[53] In contrast and over extensive lengths of time (billions of years) ecosystems have maintained a consistent balance with production roughly equaling respiratory consumption rates. The balanced recycling efficiency of nature means that production of decaying waste material has exceeded rates of recyclable consumption into food chains equal to the global stocks of fossilized fuels that escaped the chain of decomposition.[54]

text: Pesticides soon spread through everything in the ecosphere-both human technosphere and nonhuman biosphere-returning from the 'out there' of natural environments back into plant, animal, and human bodies situated at the 'in here' of artificial environments with unintended, unanticipated, and unwanted effects. By using zoological, toxicological, epidemiological, and ecological insights, Carson generated a new sense of how 'the environment' might be seen.[55]:62

text: Microplastics and nanosilver materials flowing and cycling through ecosystems from pollution and discarded technology are among a growing list of emerging ecological concerns.[56] For example, unique assemblages of marine microbes have been found to digest plastic accumulating in the worlds oceans.[57] Discarded technology is absorbed into soils and creates a new class of soils called technosols.[58] Human wastes in the Anthropocene are creating new systems of ecological recycling, novel ecosystems that have to contend with the mercury cycle and other synthetic materials that are streaming into the biodegradation chain.[59] Microorganisms have a significant role in the removal of synthetic organic compounds from the environment empowered by recycling mechanisms that have complex biodegradation pathways. The effect of synthetic materials, such as nanoparticles and microplastics, on ecological recycling systems is listed as one of the major concerns for ecosystem in this century.[56][60]

text: Technological recycling[edit]

text: Recycling in human industrial systems (or technoecosystems) differs from ecological recycling in scale, complexity, and organization. Industrial recycling systems do not focus on the employment of ecological food webs to recycle waste back into different kinds of marketable goods, but primarily employ people and technodiversity instead. Some researchers have questioned the premise behind these and other kinds of technological solutions under the banner of 'eco-efficiency' are limited in their capability, harmful to ecological processes, and dangerous in their hyped capabilities.[12][61] Many technoecosystems are competitive and parasitic toward natural ecosystems.[54][62] Food web or biologically based "recycling includes metabolic recycling (nutrient recovery, storage, etc.) and ecosystem recycling (leaching and in situ organic matter mineralization, either in the water column, in the sediment surface, or within the sediment."[63]:243