Earth Temperature Timeline
Earth Temperature Timeline
Note there are several spelling errors in the comic, so please do only correct spelling errors that are not part of the comic! See more in the trivia section .
[A large heading, followed by a sub-caption. Below that two lines with a statement in between:] A timeline of Earth’s average temperature since the last ice age glaciation When people say “The climate has changed before,” these are the kinds of changes they’re talking about.
[A very long chart below the headings above is headed with a label for the scale of the X-axis above the chart. Below that a sub-caption. To the left an arrow down to the top of the chart pointing to the dotted curves starting point (at -4.3°C below the 1961-1990 average) with a label above the arrow. And arrow pointing left to the left of the center and another pointing right to the right of the center has labels. Below these is the temperature scale of the X-axis, with 9 ticks between the borders each with a label ranging from -4 to +4°C compared to the 1961-1990 average, but with another step in each direction not labeled towards to axis so the chart covers -5 to +5°C compared to the 1961-1990 average.] Temperature Compared to the 1961-1990 average Start Colder Warmer -4°C -3°C -2°C -1°C 0°C +1°C +2°C +3°C +4°C
[To the right of the chart is a gray text standing on the side down along the outer boarder of the chart with the sources for the chart:] Source: Shakun et. al. (2012) , Marcott et. al. (2013), Annan and Hargreaves (2013) , HadCRUT 4 , IPCC
[The chart is split in 10 columns by the temperature scale and the borders. The two central columns are white, and then from there to the left the background becomes a faded color that changes from light blue to blue at the edge in four steps. Similarly to the right the color changes from light red to red. To the left there is a time scale taking 500 years leaps from 20,000 BCE all the way to year 1, where there are two years, one for BBC and one for CE. The 500 year leaps continue until 1500 CE and from there the steps are down to 100 years until 2100 with also present day 2016 labeled. After 1500 the CE is omitted. The labels stop there, but there is space below covering down to 2200 CE. There is clearly visible division line across the chart on the level of each of the 500 step, and fainter lines for each of the 100 steps all the way even though only the last 5 of these 100 steps are labeled. There is a similar clear line at 2016. Below each step on the Y-axis is noted, and then any text starting before the next step is noted below indented. If there are extra image belonging to text this is indented once more. The graph that the whole chart is about is a dotted line that begins at the “start” point mentioned above at -4.3°C and then begins to go straight down. It will change left and right all the way down. To being with all text and most drawings are to right of the dotted curve. Whenever something is to the left it will be noted. When it says to the left above something, and then nothing over the next, then the next will be to the right. Only at the very bottom are there more entries to the left than right. ] 20000 BCE [An arrow goes from the dotted line to the central line at 0°C. In the middle of the line there is a temperature label:] 4.3°C At the start of our timeline, 22,000 years ago, Earth is 4°C colder than during the late 20 th century. Boston is buried under almost a mile of ice, and the glaciers reach as far south as New York City. [The Statue of Liberty is shown in front of a glacier front. A very tiny Cueball is on top of the glacier. The drawing is labeled and so is also the glacier.] New York Ice [Cueball (wearing a knit cap with a pom-pom is seen walking in a snowy landscape leaving black footprints behind him. He walks through the white central part of the chart.] [The skyline of Boston is shown with two clear buildings among all the other. Above it is a line and in between this area has been filled with thin lines. The drawing is labeled and so is this area. Also the skyline has an arrow pointing at it with a label:] Boston Ice Modern skyline
19500 BCE But the world is about to warm up. By this time, humans have already spread across Africa, Eurasia, and Australia. They’ve created painting, pottery, rope, and bows and arrows, but haven’t developed writing or farming.
19000 BCE Changes in the Earth’s orbit mean that more sunlight reaches the polar ice… [A line chart with a labeled Y-axis with three labeled ticks. The curve starts up and then goes down five times and up four times ending down. There is one plateau towards the end compared to the rest of the curve where the ups and downs are quite alike.] Summer sun W/m 2 at 60°N 550 500 450
18500 BCE [A map of the world. At the top is a light gray area covering North America, Greenland and northern Europe and most of the northern part of Russia. A similar gray area covers Antarctica. There are two labels in the gray area above and one in the gray area below:] Ice Ice Ice
18000 BCE …And the ice sheets start to melt.
17500 BCE Temperatures have been creeping upward, but around this point, CO 2 levels start to climb…
17000 BCE …And then the warming speeds up.
16500 BCE [Cueball is standing with a spear just the right of the graph talking to a rabbit.] Cueball: Still pretty cold.
16000 BCE [Megan points to the graph to the right of her and between her and Ponytail standing on the other side. Mean is the first drawing on the left side of the dotted curve, which has hardly moved since the beginning, only to just on the other side of 4°C.] [In the right part of the chart is an explanation of the data. Below the first two lines there are four drawings each showing possible temperature swings in reality compared to the smoothed data that represents the dotted curve of the entire chart. The dotted curve is shown in all four drawings and a thin line is shown running along it but with much more fluctuation left and right on the first two, a large spike right on the third and a large bump way right on the fourth. Above these there are two labels. The first labels is inside a bracket that covers the first three, and the last label is for the last drawing. Below is a list of sources.] Limits of this data: Short warming or cooling spikes might be “smoothed out” by these reconstructions but only if they’re small or brief enough. Possible Unlikely Reconstructions are from Shakun (2012) and Marcott (2013), scaled to Annan + Hargreaves (2013) estimate for the last glacial period.
15500 BCE In what is now France, humans paint murals on the walls of the Lascaux caves [Hairy paints three animals, two with horns, and two humans, Cueball holding hand with Hairy who has a spear. On the other side of the central line Megan writes three letters, the last of which is reversed.] NIИ
15000 BCE Ice sheets around Alaska shrink, exposing a land bridge between Asia and North America [From around the bottom if this section and down to 11500 BCE the dotted curve moved steadily to the right towards warmed temperature peaking close to -1.5°C. Before this the temperature had not moved much away from that at the start.]
14500 BCE [Cueball walks right looking back at the graph behind him. Megan walks in front of him pointing further right.] Cueball: Cool. Humans reach North America.
14000 BCE The edge of the ice withdraws from New York City and retreats North. [A large glacier front speaks in a speech bubble with an arrow pointing at it. Behind is there are four peaks in the horizon and in front of it three small melting pools and some rocks on the ground.] Glacier: That’s it! I’m moving to Canada!
13500 BCE Humans domesticate dogs (Date uncertain, may be much earlier) [Megan and Cueball is watching a wolf looking at them.] Megan: Okay, you can live in our homes and we’ll feed you, but we’ll still get mad f you poop on the floor. Wolf: Deal. Cueball: And we get to breed you to be tiny and dress you in little costumes. Wolf: …Wait.
13000 BCE [Randall did not use the normal spelling for Woolly Rhino, but this is an accepted alternative spelling:] Wooly Rhino goes extinct Oregon is scoured by huge floods as glacial dams burst and lakes of meltwater flow to the sea
12500 BCE Ice sheets withdraw from Chicago
12000 BCE Humans settle Abu Hureyra in Syria
11500 BCE [An arrow on the left side of the dotted curve is pointing down along the dotted curve and to the left indicate temperature is declining again, meaning the dotted curve now moves left to colder temperatures. This only continues until 10500 BCE. It is only the second time something is noted on the left side after Megan at 16000 BCE] Temperatures start to decline, mainly in the Northern hemisphere This may be caused by changes in ocean circulation due to the floods of cold fresh meltwater flowing into the Atlantic as the North American ice sheet melts. This cooler period is called the Younger Dryas
11000 BCE [This is the first text to the left of the dotted curve:] Humans reach Argentina
10500 BCE [An arrow pointing down along the right side of the dotted curve and to the right indicate temperature is increasing again, meaning the dotted curve now moves right to hotter temperatures. This continues until 8000 BCE where it levels out just above 0°C.] Warming resumes Human settlements at Jericho
10000 BCE First development of farming
9500 BCE Saber-toothed cat goes extinct [To the left:] Horses disappear from North America
9000 BCE [To the left, Randall spelled Pokémon wrong:] Last North American Pokemon go extinct [Cueball with a speak and Megan is looking up at this last “fact”.] Megan: That is not a real fact. Temperatures reach modern levels Rising seas cut off the land bridge between North America and Asia Cattle domesticated
8500 BCE Ice sheets retreat across the Canadian border Temperatures start to level out slightly above 1961-1990 levels
8000 BCE [The above sentence breaks over the 8000 BCE line. From here a maximum in temperature on the chart is reached at 0.5°C which will not be overtaken until 2000 CE. It stays almost constant here until 5000 BCE where a slight cooling begins.]
7500 BCE [To the left:] This warm, stable period is called the Holocene Climate Optimum [To the left:] Jiahu settled in China
7000 BCE Final collapse of the North American ice sheet leads to rapid 2-4m sea level rise… [A small arrow points down and left to the right of the dotted curve. There is a small decrease in temperature but it is very small and would have been missed without the arrow and label.] …And a period of cooling in the Northern hemisphere
6500 BCE [To the left:] As seas rise to near their modern levels, Britain is cut off from mainland Europe
6000 BCE Humans develop copper metalworking
5500 BCE [To the left:] Massive volcanic eruption in Oregon creates crater lake Gold metalworking
5000 BCE [To the left:] Invention of the wheel [To the left. To the right of the dotted curve is an arrow pointing down and slightly left. From here temperature decreases very slowly but steadily from 0.5°C until 1000 BCE where a stable plateau is reached around 0°C.] Earth begins to cool slowly mainly due to regular cycles in its orbit
4500 BCE [To the left:] Proto-Indo-European language develops [To the right of the curve Ponytail holds up a hand towards Cueball.] Ponytail: Let’s make our language heavily inflected, so future students have to memorize a zillion verb endings! Cueball: Okay! [To the left:] Permanent settlements in the fertile crescent
4000 BCE Horses domesticated [To the left:] Minoan culture arises on Crete
3500 BCE Egyptian mummification Rise of the Indus Valley civilization [To the left:] Invention of writing in Sumer “prehistory” ends, “history” begins Earliest human whose name we know (Pharaoh Iry-Hor in Egypt)
3000 BCE Three Sovereigns and five emperors period in China Gilgamesh [To the left:] Imhotep Mayan culture emerges [To the left:] Great Pyramid constructed
2500 BCE Corded Ware culture in Europe [To the left of the curve two rock musicians with long hair and electrical guitars are standing on either side of a small gate made of three slabs of stone, one on top of the other two standing stones.] Stonehenge completed Chariots developed
2000 BCE [To the left:] Alphabetic writing developed in Egypt Last mammoths on a tiny Siberian island go extinct [To the left:] Minoan eruption
1500 BCE [To the left:] Iron smelting Olmec civilization develops in Central America [A Trojan horse with two Cueball-like guys in front and a third standing on its back. Its back is at three Cueball’s height and its head rises to the level of the Cueball on its back. It stands on a platform with four wheel on the visible side. There is text on the horse] Setting of the Iliad and the Odyssey Text on horse: Not a trap [To the left:] Invasion of the Sea peoples* * A real thing Polynesians explore the Pacific Ocean
1000 BCE [From 1000 BBC to 1000 CE the temperature is stable and very close to 0°C.] [To the left:] Solomon Illiad [sic] and Odyssey composed [To the left:] Rise of Greek city-states Neo-Assyrian empire [To the left:] First Olympics Zapotec writing in modern Mexico [To the left:] Confucius
500 BCE [To the left:] The stuff in the 300 (film)|movie 300 , but regular speed and with more clothing Buddha Nazca Lines [To the left:] Alexander the Great [To the left:] Mayan hieroglyphics Ashoka the Great [To the left:] Paper invented [To the left:] Asterix Teotihuacán metropolis [To the left:] Julius Caesar
[At the year 0, there is instead two numbers for each of the two scales before and after Christ:] 1 BCE 1 CE [To the left:] Roman Empire Jesus [To the left and erupting volcano.] Pompeii Three Kingdoms period [To the left:] Gupta empire [To the left:] Various groups take turns sacking Rome Attila the Hun
500 CE Muhammad [To the left:] Tang Dynasty [An arrow to the right of the dotted curve pointing down, takes a swing far out from the curve and then bends back again. The text label next to it breaks into the next 500 period. The dotted curve stays stable at 0°C along this arrow.] Medieval warm period in Europe and some northern regions (too regional to affect the global average much) [To the left:] Leif Eriksson
1000 CE [The dotted curve moves to the left towards lower temperature reaching a minimum around 1650 of about -0.6°C at the Little Ice Age.] [To the left a drawing of a compass with needle pointing the black end towards north east. There are labels for the four main directions and a label next to it:] N W E S Magnetic compass navigation [To the left:] Ghengis [sic] Khan Zheng He’s fleet explores Asia and Africa [To the left:] Aztec Alliance [To the left:] Printing press [To the left:] Columbus
1500 CE European Renaissance [To the left:] Shakespeare
1600 [To the left:] Newton [To the right of the dotted curve there is an arrow pointing down that makes a swing in towards the curve and then back out again. At -0.6°C this is the coldest it has been since 9500 BCE. It is labeled:] ”Little Ice Age”
1700 Steam engines [To the left:] Unites States Independence
1800 Industrial Revolution [To the left:] Telegraphs [After this the dotted curve becomes solid.]
1900 [To the left, and on the line for 1900:] Airplanes [To the left:] World Wars [The solid line takes a step to the right close to 0°C. Over the rest of the 1900s it moves closer to 0°C crossing it before 2000 where it almost reaches the maximum temperature of 0.5 °C from earlier in 8000 BCE.] Fossil fuel CO 2 emissions start rapidly increasing [To the left:] Nuclear weapons [To the left:] Internet
2000 Northwest Passage opens [From here to present day the solid line increases rapidly and in 2016 present day is almost reaches 1°C, with about 0.8°C.]
2016 [To the left on the line for 2016:] Present day [From here the curve once again becomes dotted as this is the future. After one dot it splits in two and after the first two dots another split between them occurs forming three possible future dotted curves. The first curve bending down before the others, and thus to the right of the other two reaches about 1.2°C and then goes straight down and stops at the 2100 line. An arrow points to it from the left and a label is written patly before and the rest after the 2100 line to the left of the curve:] Best-case scenario assuming immediate massive action to limit emissions
2100 [The middle curve bends a little down after reaching 1.3°C and then continues this path reaching 2°C in 2100. An arrow point from below to it and a label is written below the curve and below 2100 line:] Optimistic scenario [The last line continues along the path from the last 16 years of the solid line reaching 4.2°C at 2100, almost as far on the other side of 0°C in 150 years as it took 14000 years to move from the other side from the start of the chart. Another arrow point to this from below with a label below the curve and below 2100 line:] Current Path
This comic became popular with a much broader audience than most xkcd comics. It was discussed admiringly by news sites such as Popular Science , Reason , Slate , Smithsonian , Forbes , Vox , NPR , Quartz , Science Alert and Climate Central . It was promoted by famous individuals such as Elon Musk and even twitted by the UN council on Climate Change , and obviously hated on by vocal climate change deniers and cranks such as Anthony Watts debunked and Joanne Nova debunked
Saying the "dotted line comes from computer models" is a bit inaccurate. Prehistoric temperature reconstructions are based on lots of measurements from lots of places around the planet: ice cores, lake and ocean sediments, etc. which are the best proxy records of climate change. From those measurements, one infers temperature, so Randall Munroe may be more correct than he realises . Calling that process computer modeling stretches the meaning of the phrase. For more rationalist critique of this chart not driven by the agenda of pushing pseudoscientific beliefs which are against the worldwide consensus, see t h i s and most insightfully, this .
Note: Since a lot of new people are here looking for this chart today, I'll be posting Wednesday's comic on Thursday instead. Before that, the normal heading with the release day of xkcd was shown. This was (of course) still there Tuesday the day after the release, because it was first on Wednesday there were reason to note the delay. It stayed in place even for some time after the "Wednesday" comic was released on Thursday, but was then removed before noon (EST) on Thursday. Randall did thus not post a link to this comic in the header text for new visitors to use, only giving them that one extra day. Even though the next comic was released on a Thursday, the scheduled Friday comic 1734: Reductionism was still released as planned. This was also the first time this occurred on xkcd - see this trivia item from the Friday comic.

This comic is a timeline on how the temperature has changed from 20,000 BCE (Before Common Era ) to the present day (2016), with three predictions for the rest of the 21st century depending on what actions are taken (or not taken) to stop CO₂ emission. This comic is a direct, but much more thorough, follow up on the previous global warming comic: 1379: 4.5 Degrees . By having readers scroll through millennia of slow-paced natural changes, Randall uses the comic to confront the rapid temperature rise in recent years.
Over the past 100 years, human action has produced a large amount of CO₂ emissions , which have caused a rise in average global temperature through the greenhouse effect . This is called global warming and is part of a climate change , a subject that has become a recurrent subject on xkcd. There are still many people who claim that this is not happening, or at least that it is not caused by any human actions, called climate change deniers . One argument of theirs is that global warming is happening for natural causes, summarized with the phrase "temperature has changed before".
This comic shows that while temperature changes have indeed occurred before, the speed of the current temperature rise is much, much faster than those measured for many previous thousands of years. The comic became so popular that Randall postponed the release of his next comic to keep this one on the front page one day longer.
The temperature curve is a dotted line most of the time, but from about 1850 to 2016 the measurement data is good enough to let the curve become a solid line indicating that this is not an estimate. Before 1850 the temperature is an estimate based on the sources given. And likewise into the future the three possible curves are also dotted to show that they are predictions, based on how seriously the population of Earth takes knowledge (and comics) like this.
Although this is a topic Randall obviously takes very seriously, and by far most of the facts fit with known history, he still includes several jokes in the comic . See also the table explaining each item in the comic. After the election of Donald Trump for president later the year of this comic's release, it is possible that Randall believes that his worst fears (as expressed by the current path at the bottom) will hold up, with the actions taken by the new president.
The title text compares the saying that "the temperature has changed before" comparing temperature changes over thousands of years to the rapid global warming over the last century with saying that the "small" changes to the temperature a car experiences over the years of normal usage should not make you worried over the rapid temperature increase that happens when someone sets your car on fire. Randall previously used this joke in 1693: Oxidation .
The image attributes climate data sources as "Shakun et al. (2012), Marcott et al. (2013), Annan and Hargreaves (2013), HadCRUT4, IPCC":
Note there are several spelling errors in the comic, so please do only correct spelling errors that are not part of the comic! See more in the trivia section .
[A large heading, followed by a sub-caption. Below that two lines with a statement in between:] A timeline of Earth’s average temperature since the last ice age glaciation When people say “The climate has changed before,” these are the kinds of changes they’re talking about.
[A very long chart below the headings above is headed with a label for the scale of the X-axis above the chart. Below that a sub-caption. To the left an arrow down to the top of the chart pointing to the dotted curves starting point (at -4.3°C below the 1961-1990 average) with a label above the arrow. And arrow pointing left to the left of the center and another pointing right to the right of the center has labels. Below these is the temperature scale of the X-axis, with 9 ticks between the borders each with a label ranging from -4 to +4°C compared to the 1961-1990 average, but with another step in each direction not labeled towards to axis so the chart covers -5 to +5°C compared to the 1961-1990 average.] Temperature Compared to the 1961-1990 average Start Colder Warmer -4°C -3°C -2°C -1°C 0°C +1°C +2°C +3°C +4°C
[To the right of the chart is a gray text standing on the side down along the outer boarder of the chart with the sources for the chart:] Source: Shakun et. al. (2012) , Marcott et. al. (2013), Annan and Hargreaves (2013) , HadCRUT 4 , IPCC
[The chart is split in 10 columns by the temperature scale and the borders. The two central columns are white, and then from there to the left the background becomes a faded color that changes from light blue to blue at the edge in four steps. Similarly to the right the color changes from light red to red. To the left there is a time scale taking 500 years leaps from 20,000 BCE all the way to year 1, where there are two years, one for BBC and one for CE. The 500 year leaps continue until 1500 CE and from there the steps are down to 100 years until 2100 with also present day 2016 labeled. After 1500 the CE is omitted. The labels stop there, but there is space below covering down to 2200 CE. There is clearly visible division line across the chart on the level of each of the 500 step, and fainter lines for each of the 100 steps all the way even though only the last 5 of these 100 steps are labeled. There is a similar clear line at 2016. Below each step on the Y-axis is noted, and then any text starting before the next step is noted below indented. If there are extra image belonging to text this is indented once more. The graph that the whole chart is about is a dotted line that begins at the “start” point mentioned above at -4.3°C and then begins to go straight down. It will change left and right all the way down. To being with all text and most drawings are to right of the dotted curve. Whenever something is to the left it will be noted. When it says to the left above something, and then nothing over the next, then the next will be to the right. Only at the very bottom are there more entries to the left than right. ] 20000 BCE [An arrow goes from the dotted line to the central line at 0°C. In the middle of the line there is a temperature label:] 4.3°C At the start of our timeline, 22,000 years ago, Earth is 4°C colder than during the late 20 th century. Boston is buried under almost a mile of ice, and the glaciers reach as far south as New York City. [The Statue of Liberty is shown in front of a glacier front. A very tiny Cueball is on top of the glacier. The drawing is labeled and so is also the glacier.] New York Ice [Cueball (wearing a knit cap with a pom-pom is seen walking in a snowy landscape leaving black footprints behind him. He walks through the white central part of the chart.] [The skyline of Boston is shown with two clear buildings among all the other. Above it is a line and in between this area has been filled with thin lines. The drawing is labeled and so is this area. Also the skyline has an arrow pointing at it with a label:] Boston Ice Modern skyline
19500 BCE But the world is about to warm up. By this time, humans have already spread across Africa, Eurasia, and Australia. They’ve created painting, pottery, rope, and bows and arrows, but haven’t developed writing or farming.
19000 BCE Changes in the Earth’s orbit mean that more sunlight reaches the polar ice… [A line chart with a labeled Y-axis with three labeled ticks. The curve starts up and then goes down five times and up four times ending down. There is one plateau towards the end compared to the rest of the curve where the ups and downs are quite alike.] Summer sun W/m 2 at 60°N 550 500 450
18500 BCE [A map of the world. At the top is a light gray area covering North America, Greenland and northern Europe and most of the northern part of Russia. A similar gray area covers Antarctica. There are two labels in the gray area above and one in the gray area below:] Ice Ice Ice
18000 BCE …And the ice sheets start to melt.
17500 BCE Temperatures have been creeping upward, but around this point, CO 2 levels start to climb…
17000 BCE …And then the warming speeds up.
16500 BCE [Cueball is standing with a spear just the right of the graph talking to a rabbit.] Cueball: Still pretty cold.
16000 BCE [Megan points to the graph to the right of her and between her and Ponytail standing on the other side. Mean is the first drawing on the left side of the dotted curve, which has hardly moved since the beginning, only to just on the other side of 4°C.] [In the right part of the chart is an explanation of the data. Below the first two lines there are four drawings each showing possible temperature swings in reality compared to the smoothed data that represents the dotted curve of the entire chart. The dotted curve is shown in all four drawings and a thin line is shown running along it but with much more fluctuation left and right on the first two, a large spike right on the third and a large bump way right on the fourth. Above these there are two labels. The first labels is inside a bracket that covers the first three, and the last label is for the last drawing. Below is a list of sources.] Limits of this data: Short warming or cooling spikes might be “smoothed out” by these reconstructions but only if they’re small or brief enough. Possible Unlikely Reconstructions are from Shakun (2012) and Marcott (2013), scaled to Annan + Hargreaves (2013) estimate for the last glacial period.
15500 BCE In what is now France, humans paint murals on the walls of the Lascaux caves [Hairy paints three animals, two with horns, and two humans, Cueball holding hand with Hairy who has a spear. On the other side of the central line Megan writes three letters, the last of which is reversed.] NIИ
15000 BCE Ice sheets around Alaska shrink, exposing a land bridge between Asia and North America [From around the bottom if this section and down to 11500 BCE the dotted curve moved steadily to the right towards warmed temperature peaking close to -1.5°C. Before this the temperature had not moved much away from that at the start.]
14500 BCE [Cueball walks right looking back at the graph behind him. Megan walks in front of him pointing further right.] Cueball: Cool. Humans reach North America.
14000 BCE The edge of the ice withdraws from New York City and retreats North. [A large glacier front speaks in a speech bubble with an arrow pointing at it. Behind is there are four peaks in the horizon and in front of it three small melting pools and some rocks on the ground.] Glacier: That’s it! I’m moving to Canada!
13500 BCE Humans domesticate dogs (Date uncertain, may be much earlier) [Megan and Cueball is watching a wolf looking at them.] Megan: Okay, you can live in our homes and we’ll feed you, but we’ll still get mad f you poop on the floor. Wolf: Deal. Cueball: And we get to breed you to be tiny and dress you in little costumes. Wolf: …Wait.
13000 BCE [Randall did not use the normal spelling for Woolly Rhino, but this is an accepted alternative spelling:] Wooly Rhino goes extinct Oregon is scoured by huge floods as glacial dams burst and lakes of meltwater flow to the sea
12500 BCE Ice sheets withdraw from Chicago
12000 BCE Humans settle Abu Hureyra in Syria
11500 BCE [An arrow on the left side of the dotted curve is pointing down along the dotted curve and to the left indicate temperature is declining again, meaning the dotted curve now moves left to colder temperatures. This only continues until 10500 BCE. It is only the second time something is noted on the left side after Megan at 16000 BCE] Temperatures start to decline, mainly in the Northern hemisphere This may be caused by changes in ocean circulation due to the floods of cold fresh meltwater flowing into the Atlantic as the North American ice sheet melts. This cooler period is called the Younger Dryas
11000 BCE [This is the first text to the left of the dotted curve:] Humans reach Argentina
10500 BCE [An arrow pointing down along the right side of the dotted curve and to the right indicate temperature is increasing again, meaning the dotted curve now moves right to hotter temperatures. This continues until 8000 BCE where it levels out just above 0°C.] Warming resumes Human settlements at Jericho
10000 BCE First development of farming
9500 BCE Saber-toothed cat goes extinct [To the left:] Horses disappear from North America
9000 BCE [To the left, Randall spelled Pokémon wrong:] Last North American Pokemon go extinct [Cueball with a speak and Megan is looking up at this last “fact”.] Megan: That is not a real fact. Temperatures reach modern levels Rising seas cut off the land bridge between North America and Asia Cattle domesticated
8500 BCE Ice sheets retreat across the Canadian border Temperatures start to level out slightly above 1961-1990 levels
8000 BCE [The above sentence breaks over the 8000 BCE line. From here a maximum in temperature on the chart is reached at 0.5°C which will not be overtaken until 2000 CE. It stays almost constant here until 5000 BCE where a slight cooling begins.]
7500 BCE [To the left:] This warm, stable period is called the Holocene Climate Optimum [To the left:] Jiahu settled in China
7000 BCE Final collapse of the North American ice sheet leads to rapid 2-4m sea level rise… [A small arrow points down and left to the right of the dotted curve. There is a small decrease in temperature but it is very small and would have been missed without the arrow and label.] …And a period of cooling in the Northern hemisphere
6500 BCE [To the left:] As seas rise to near their modern levels, Britain is cut off from mainland Europe
6000 BCE Humans develop copper metalworking
5500 BCE [To the left:] Massive volcanic eruption in Oregon creates crater lake Gold metalworking
5000 BCE [To the left:] Invention of the wheel [To the left. To the right of the dotted curve is an arrow pointing down and slightly left. From here temperature decreases very slowly but steadily from 0.5°C until 1000 BCE where a stable plateau is reached around 0°C.] Earth begins to cool slowly mainly due to regular cycles in its orbit
4500 BCE [To the left:] Proto-Indo-European language develops [To the right of the curve Ponytail holds up a hand towards Cueball.] Ponytail: Let’s make our language heavily inflected, so future students have to memorize a zillion verb endings! Cueball: Okay! [To the left:] Permanent settlements in the fertile crescent
4000 BCE Horses domesticated [To the left:] Minoan culture arises on Crete
3500 BCE Egyptian mummification Rise of the Indus Valley civilization [To the left:] Invention of writing in Sumer “prehistory” ends, “history” begins Earliest human whose name we know (Pharaoh Iry-Hor in Egypt)
3000 BCE Three Sovereigns and five emperors period in China Gilgamesh [To the left:] Imhotep Mayan culture emerges [To the left:] Great Pyramid constructed
2500 BCE Corded Ware culture in Europe [To the left of the curve two rock musicians with long hair and electrical guitars are standing on either side of a small gate made of three slabs of stone, one on top of the other two standing stones.] Stonehenge completed Chariots developed
2000 BCE [To the left:] Alphabetic writing developed in Egypt Last mammoths on a tiny Siberian island go extinct [To the left:] Minoan eruption
1500 BCE [To the left:] Iron smelting Olmec civilization develops in Central America [A Trojan horse with two Cueball-like guys in front and a third standing on its back. Its back is at three Cueball’s height and its head rises to the level of the Cueball on its back. It stands on a platform with four wheel on the visible side. There is text on the horse] Setting of the Iliad and the Odyssey Text on horse: Not a trap [To the left:] Invasion of the Sea peoples* * A real thing Polynesians explore the Pacific Ocean
1000 BCE [From 1000 BBC to 1000 CE the temperature is stable and very close to 0°C.] [To the left:] Solomon Illiad [sic] and Odyssey composed [To the left:] Rise of Greek city-states Neo-Assyrian empire [To the left:] First Olympics Zapotec writing in modern Mexico [To the left:] Confucius
500 BCE [To the left:] The stuff in the 300 (film)|movie 300 , but regular speed and with more clothing Buddha Nazca Lines [To the left:] Alexander the Great [To the left:] Mayan hieroglyphics Ashoka the Great [To the left:] Paper invented [To the left:] Asterix Teotihuacán metropolis [To the left:] Julius Caesar
[At the year 0, there is instead two numbers for each of the two scales before and after Christ:] 1 BCE 1 CE [To the left:] Roman Empire Jesus [To the left and erupting volcano.] Pompeii Three Kingdoms period [To the left:] Gupta empire [To the left:] Various groups take turns sacking Rome Attila the Hun
500 CE Muhammad [To the left:] Tang Dynasty [An arrow to the right of the dotted curve pointing down, takes a swing far out from the curve and then bends back again. The text label next to it breaks into the next 500 period. The dotted curve stays stable at 0°C along this arrow.] Medieval warm period in Europe and some northern regions (too regional to affect the global average much) [To the left:] Leif Eriksson
1000 CE [The dotted curve moves to the left towards lower temperature reaching a minimum around 1650 of about -0.6°C at the Little Ice Age.] [To the left a drawing of a compass with needle pointing the black end towards north east. There are labels for the four main directions and a label next to it:] N W E S Magnetic compass navigation [To the left:] Ghengis [sic] Khan Zheng He’s fleet explores Asia and Africa [To the left:] Aztec Alliance [To the left:] Printing press [To the left:] Columbus
1500 CE European Renaissance [To the left:] Shakespeare
1600 [To the left:] Newton [To the right of the dotted curve there is an arrow pointing down that makes a swing in towards the curve and then back out again. At -0.6°C this is the coldest it has been since 9500 BCE. It is labeled:] ”Little Ice Age”
1700 Steam engines [To the left:] Unites States Independence
1800 Industrial Revolution [To the left:] Telegraphs [After this the dotted curve becomes solid.]
1900 [To the left, and on the line for 1900:] Airplanes [To the left:] World Wars [The solid line takes a step to the right close to 0°C. Over the rest of the 1900s it moves closer to 0°C crossing it before 2000 where it almost reaches the maximum temperature of 0.5 °C from earlier in 8000 BCE.] Fossil fuel CO 2 emissions start rapidly increasing [To the left:] Nuclear weapons [To the left:] Internet
2000 Northwest Passage opens [From here to present day the solid line increases rapidly and in 2016 present day is almost reaches 1°C, with about 0.8°C.]
2016 [To the left on the line for 2016:] Present day [From here the curve once again becomes dotted as this is the future. After one dot it splits in two and after the first two dots another split between them occurs forming three possible future dotted curves. The first curve bending down before the others, and thus to the right of the other two reaches about 1.2°C and then goes straight down and stops at the 2100 line. An arrow points to it from the left and a label is written patly before and the rest after the 2100 line to the left of the curve:] Best-case scenario assuming immediate massive action to limit emissions
2100 [The middle curve bends a little down after reaching 1.3°C and then continues this path reaching 2°C in 2100. An arrow point from below to it and a label is written below the curve and below 2100 line:] Optimistic scenario [The last line continues along the path from the last 16 years of the solid line reaching 4.2°C at 2100, almost as far on the other side of 0°C in 150 years as it took 14000 years to move from the other side from the start of the chart. Another arrow point to this from below with a label below the curve and below 2100 line:] Current Path
This comic became popular with a much broader audience than most xkcd comics. It was discussed admiringly by news sites such as Popular Science , Reason , Slate , Smithsonian , Forbes , Vox , NPR , Quartz , Science Alert and Climate Central . It was promoted by famous individuals such as Elon Musk and even twitted by the UN council on Climate Change , and obviously hated on by vocal climate change deniers and cranks such as Anthony Watts debunked and Joanne Nova debunked
Saying the "dotted line comes from computer models" is a bit inaccurate. Prehistoric temperature reconstructions are based on lots of measurements from lots of places around the planet: ice cores, lake and ocean sediments, etc. which are the best proxy records of climate change. From those measurements, one infers temperature, so Randall Munroe may be more correct than he realises . Calling that process computer modeling stretches the meaning of the phrase. For more rationalist critique of this chart not driven by the agenda of pushing pseudoscientific beliefs which are against the worldwide consensus, see t h i s and most insightfully, this .
Note: Since a lot of new people are here looking for this chart today, I'll be posting Wednesday's comic on Thursday instead. Before that, the normal heading with the release day of xkcd was shown. This was (of course) still there Tuesday the day after the release, because it was first on Wednesday there were reason to note the delay. It stayed in place even for some time after the "Wednesday" comic was released on Thursday, but was then removed before noon (EST) on Thursday. Randall did thus not post a link to this comic in the header text for new visitors to use, only giving them that one extra day. Even though the next comic was released on a Thursday, the scheduled Friday comic 1734: Reductionism was still released as planned. This was also the first time this occurred on xkcd - see this trivia item from the Friday comic.
