Editing 1732: Earth Temperature Timeline

{{comic
| number    = 1732
| date      = September 12, 2016
| title     = Earth Temperature Timeline
| before    = [[#Explanation|↓ Skip to explanation ↓]]
| image     = earth_temperature_timeline.png
| titletext = [After setting your car on fire] Listen, your car's temperature has changed before.
}}

{{TOC}} 
==Explanation==
This comic is a [[:Category:Timelines|timeline]] on how the temperature has changed from 20,000 BCE (Before {{w|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 {{w|CO₂ emissions}}, which have caused a rise in average global temperature through the {{w|greenhouse effect}}. This is called {{w|global warming}} and is part of a {{w|climate change}}, a subject that has become a [[:Category:Climate change|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 {{w|Climate change denial|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]] [[#Popularity_of_comic|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|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|jokes in the comic]]. See also the [[#Table of all elements|table]] explaining each item in the comic. After the election of {{w|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]].

===Jokes in the comic===
* By placing the invention of the internet at 1980 in the chart, just where the temperature curve starts its most rapid increase, Randall humorously implies that the internet caused the rise in temperature.
* At 13600 BCE a glacier is shown retreating from New York because of the warm up. It is disgusted by the new changes and proclaims: ''That’s it! I’m moving to Canada!'' This is a joke on [https://www.rollingstone.com/politics/politics-news/want-to-move-to-canada-if-trump-wins-not-so-fast-100658/ an idiom said by US citizens] to protest against changes in their country. As shown in the chart, the glacier takes 5000 years (13600-8400 BCE) to cross what would become the Canadian border (neither the United States nor Canada existed yet).{{citation needed}} Also, glaciers don't speak English, or any language for that matter.{{Citation needed}}
* At 13400 BCE it is mentioned that {{w|origin of the domestic dog|humans domesticate dogs}}. [[Megan]] talks to a wolf about to be tamed making a deal with it, that it can eat and sleep with the humans as long as they can yell at it for pooping indoors. This sounds like a sweet deal for the wolf until [[Cueball]] mentions that they will {{w|Dog breeding|breed}} it to be {{w|Chihuahua (dog)|very small}} and then dress it up in small {{w|Dog's fashion|costumes}}. The wolf says wait, but it is already too late...
* The {{w|Pokémon}} reference at 9000 BCE about them going extinct in North America (although Megan, immediately underneath, does note that this is not a real fact). As the writing stated that ''Pokemon go extinct'' this can also be seen as a reference to a popular video game called {{w|Pokémon Go}} and hence also the comic [[1705|1705: Pokémon Go]].
* At 4500 BCE, next to "{{w|Proto-Indo-European language}} develops", [[Ponytail]] gets the idea to develop the language heavily inflected to make it difficult to remember all the verb endings for future students. This is a direct reference to the comic [[1709: Inflection]].
* The reference to the 1984 {{w|mockumentary}} about the fake rock band {{w|This Is Spinal Tap}} in conjunction with {{w|Stonehenge}} at 2200 BCE. In the movie the band ordered a giant 18 feet Stonehenge megalith but a writing mistake gives them one that is only 18 inches high.
**Another real band {{w|Nine Inch Nails}} is referenced 16000 BCE where Megan writes the band's stylized name NIИ on the wall next to [[Hairy]] who is in the process of painting the {{w|cave painting}} at {{w|Lascaux}} in France.
* Around the setting of the {{w|Iliad}} and the {{w|Odyssey}} (1200 BCE) a drawing of the {{w|Trojan Horse}} has writing on it that states: ''Not a trap''. 
* Just below the previous entry also at 1200 BCE is the mentioning of the invasion of the {{w|Sea Peoples}}. This sounds so much like a reference to {{w|Mermaid|mermaids}}, often called {{w|Mermaid#One_Thousand_and_One_Nights|sea people}} that Randall feels the need to note that this invasion and these sea people is ''a real thing'' in a footnote. This is opposed to the Pokémon reference above where he notes that it is ''not a real fact''. The sea people was a seafaring confederation of groups known to have attacked ancient Egypt and other Bronze age civilizations around this time. It is widely regarded to be one of the major causes of the {{w|Late Bronze Age collapse|Bronze Age Collapse}}.
* The reference at 450 BCE compares the {{w|Battle of Thermopylae}} (also known as 300 Spartans) with the dramatized 2007 movie ''{{w|300 (film)|300}}'', but in the real world the fighting of course occurred [https://youtu.be/FCfdyroV7kc?t=12 at regular speed and with more clothing].
*There are other minor jokes but this list mentions all the major jokes.

===Table of all elements===
*Here is table including all elements in the chart with explanations including reading off temperature and year for each event from the curve.
**The year group is just an easy way to find the section.
**Element is a description mainly taken from the transcript. 
**The actual year of an event has been read off more precisely on the chart.
***The central part of the element has mainly been used.
***Only rarely has ranges below 100 years been used but if a location is clearly midway between two hundred years intervals 50 year range has been used. 
***Only when there are several posts close to each other has smaller range been used a few times.
**T (°C) is the number of degrees Celsius above or below the 1961-1990 average, which on this graph is set to zero, (i.e. not the number of physical degrees above or below this 0°C).
***These have been read of to 0.1°C rounding up or down. Lines have been inserted over the chart, 10 for each degree, to make this as accurate as possible.
***In a few cases where a maximum is reached 0.05°C has been used
**Explanation of each element.
{| class="wikitable"
!Year group
!Element
!Year
!T (°C)
!Explanation
|-
| rowspan="2"| 20000 <small>BCE</small>
| [An arrow goes from the dotted line to the central line at 0°C (representing the 1961-1990 average). In the middle of the line there is a temperature label:] 4.3°C<br>At the start of our timeline, 22,000 years ago, Earth is 4°C colder than during the late 20<sup>th</sup> century. || 20000 BCE || -4.3 || The scale here is relative, showing the magnitude of change rather than an absolute temperature reading. As a rule, {{w|climate}} changes are compared with a 30 year interval, and  the 1961-1990 average was {{w|Climate#Definition|chosen for convenience}} as the "normal" to compare temperature changes with, but any other choice of baseline would show the exact same changes. The {{w|Last glacial period}} (aka ice age) reached its {{w|Last Glacial Maximum|maximum extent}} approximately 22 to 24 thousand years ago.
|-

| {{w|Boston}} is buried under almost a mile of ice, and the {{w|glaciers}} reach as far south as {{w|New York City}}.<br> [The Statue of Liberty is shown in front of a glacier front. [[Knit Cap]] is seen in the snowy landscape. The skyline of Boston is shown under a half a mile of ice.] || 19700 BCE || -4.3 || This shows what a difference 4 degree in global temperature means (massive effect), as opposed to four degrees on a daily weather wise scale (trivial). The Boston image is directly taken from [[1225: Ice Sheets]] about the ice age glacier coverage; it was also shown buried in ice in [[1379: 4.5 Degrees]].
|-
| rowspan="3"| 19500 <small>BCE</small>
| But the world is about to warm up. || 19500 BCE|| -4.3 || The warming process actually takes thousands of years, which this comic will portray down thousands of pixels to come. This is not a fast warm up, especially not compared to the one we are currently experiencing (at the bottom of the chart).
|-
| By this time, humans have already spread across {{w|Africa}}, {{w|Eurasia}}, and {{w|Australia}}. || 19300 BCE || -4.3 || {{w|Homo Sapiens}} successfully {{w|Recent_African_origin_of_modern_humans#Movement_out_of_Africa|migrated out of Africa}} somewhere between {{w|Recent_African_origin_of_modern_humans#Dating:_pre-or_post-Toba|130,000}} and {{w|Recent_African_origin_of_modern_humans#Coastal_route|70,000}} BCE.
|-
| They’ve created {{w|painting}}, {{w|pottery}}, {{w|rope}}, and {{w|Bow and arrow|bows and arrows}}, but haven’t developed {{w|writing}} or {{w|farming}}. || 19100 BCE || -4.3 || The {{w|History of painting#Pre-history|oldest known paintings}} date back to about 38,000 BCE. The {{w|Ceramic_art#History|oldest known pottery}} date back to about 20,000 BCE. The {{w|Rope#History|oldest known rope}} date back to about 26,000 BCE. The {{w|History_of_archery#Stone_Age_and_Bronze_Age_archery|oldest known arrows}} date back to about 70,000 BCE, but Randall seems to be mistaken about the bows which seems to be {{w|History_of_archery#Stone_Age_and_Bronze_Age_archery|at most 10,000 years old}}. Writing is mentioned again at 3500 BCE and farming at 10,000 BCE.

|-
| rowspan="2"| 19000 <small>BCE</small>
| Changes in the Earth’s orbit mean that more sunlight reaches the polar ice… || 18600 BCE || -4.2 ||{{w|Milankovitch cycles}} are repeated climate variations on a timescale of tens of millennia caused by cyclic variations in {{w|Orbital eccentricity|eccentricity}}, {{w|axial tilt}}, and {{w|precession}} of the {{w|Earth's orbit}}, which thus then determined climatic patterns on Earth. The Milankovitch cycles are referenced again around 4700 BCE.

|-
| [A line chart with a labeled Y-axis "Summer sun W/m<sup>2</sup> at 60°N" with three labeled ticks ranging from 450-550. 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.] || 18600 BCE || -4.2 || The chart shows the input of sun during summer time in the {{w|Northern hemisphere}} (at {{w|60° northern latitude}}) as the effect (W) per square meter (m<sup>2</sup>) which fluctuated in the range from 450-550 during the time shown in the chart. There is, however, no scale for the time between the peaks. This chart relates to the text about increasing sun to the polar ice in the entry above.
	
|-
| rowspan="1"| 18500 <small>BCE</small>
| [A map of the world. At the top is a light gray area covering {{w|North America}}, {{w|Greenland}} and northern {{w|Europe}} and most of the northern part of {{w|Russia}}. A similar gray area covers {{w|Antarctica}}. The gray areas are labeled as ice.] || 18300 BCE || -4.2 || This [[:Category:Maps|map]] shows where the ice covered the {{w|northern hemisphere}} (and Antarctica) during the {{w|Last Glacial Maximum}}. The continents have not moved much since then, but the lower water level caused by the amount of water bound up in the ice, can clearly be seen in several locations. For instance, the {{w|British islands}}, Greenland, and {{w|Papua New Guinea}} are connected to their respective neighboring continents. Also {{w|Alaska}} and Russia are connected through the ice sheets covering the northern part of the Earth.
|-
| rowspan="1"| 18000 <small>BCE</small>
| …And the ice sheets start to melt. || 17900 BCE || -4.1 || This was a slow process that takes 10,000 years. The ice is mentioned again at 13,600 and 8400 BCE.

|-
| rowspan="1"| 17500 <small>BCE</small>
| Temperatures have been creeping upward, but around this point, CO<sub>2</sub> levels start to climb…|| 17300 BCE || -4.1 || Due to the release of gasses from various sources (dissolved in the ocean, trapped in {{w|permafrost}}, etc), {{w|Carbon dioxide in Earth's_atmosphere#Measuring ancient-Earth carbon dioxide concentration|atmospheric CO<sub>2</sub> levels}} increased by 100 parts per million over a span of thousands of years. Modern civilization has added the same amount in a single century.

|-
| rowspan="1"| 17000 <small>BCE</small>
| …And then the warming speeds up. || 16700 BCE || -4.1 || It took 3000 years for the temperature to increase with one degree. So this sentence can be seen as sarcasm about the rate of natural climate change compared to modern {{w|anthropogenic}} (human caused) warming.

|-
| rowspan="1"| 16500 <small>BCE</small>
| [Cueball is standing with a spear just the right of the graph talking to a rabbit.]<br>Cueball: Still pretty cold. || 16200 BCE || -4.0 || True, because although the temperature has risen with 0.3°C over the last 4000 years, it's still 4°C below the 1961-1990 average.

|-
| rowspan="2"| 16000 <small>BCE</small>
| [Megan touches the dotted line to the right of her, with Ponytail standing on the other side. The graph has finally passed the -4°C line below the 1961-1990 average.] || 15600 BCE || -3.9 || Megan is the first drawing on the left side of the curve. She seems to be pushing the temperature up.
|-
| [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.] <br>Limits of this data: <br> Short warming or cooling spikes might be “smoothed out” by these reconstructions but only if they’re small or brief enough. <br> Possible Unlikely<br>Reconstructions are from Shakun (2012) and Marcott (2013), scaled to Annan + Hargreaves (2013) estimate for the last glacial period. || 15600 BCE || -3.9 || This is Randall's pre-emptive response to skepticism about the accuracy of prehistoric data. {{w|Ice cores}} and similar records might miss individual year-to-year variation, but should catch sustained changes lasting many decades, which is the time scale that matters for climate. See links to the [[#Sources|sources below]].

|-
| rowspan="1"| 15500 <small>BCE</small>
| In what is now {{w|France}}, humans paint murals on the walls of the {{w|Lascaux}} caves <br> [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 || 15200 BCE || -3.8 || A reference to the industrial techno band {{w|Nine Inch Nails}} as Megan writes the bands stylized name NIИ on the wall next to Hairy who is in the process of painting part of the {{w|cave paintings}} at Lascaux in France.

|-
| rowspan="1"| 15000 <small>BCE</small>
| Ice sheets around {{w|Alaska}} shrink, exposing a land bridge between Asia and North America <br> [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 below the 1961-1990 average. Before this the temperature had not moved much away from that at the start.] || 14600 BCE || -3.5 || This land bridge is known as {{w|Beringia}}. It is mentioned again at 8300 when it disappears due to the rising seas.
|-
| rowspan="1"| 14500 <small>BCE</small>
| [Cueball walks right looking back at the graph behind him. Megan walks in front of him pointing further right.]<br> Cueball: Cool.<br> Humans reach {{w|North America}}. || 14200 BCE || -3.3 || This is approximately when the humans from {{w|Asia}} crossed the land bridge mentioned in the previous entry, from what is now {{w|Siberia}} to what is now {{w|Alaska}}. {{w|Settlement of the Americas}} occurred around the time shown in the chart, although {{w|Settlement_of_the_Americas#Chronology|it's possible}} that earlier humans did so by boat prior to the formation of the land bridge.<br>Cueball's comment is a double entendre; it was figuratively "cool" that early people migrated this far, and the climate was literally cool compared to modern times.

|-
| rowspan="2"| 14000 <small>BCE</small>
| The edge of the ice withdraws from {{w|New York City}} and retreats north. || 13700 BCE || -3.1 || Even though the ice began to melt 4000 years before (at 18,000 BCE in the chart) it is first now that New York City is free of ice.
|-
| [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.] <br> Glacier: ''That’s it! I’m moving to Canada!'' || 13600 BCE || -3.0 || When US citizens are unhappy with changes in their country, they sometimes say they will move to Canada in protest. Here it is the glacier that is anthropomorphically unhappy with the climate changes. However this is a slow process; it crosses the Canadian border more than 5000 years later.

|-
| rowspan="2"| 13500 <small>BCE</small>
| Humans domesticate dogs <br> (Date uncertain, may be much earlier) || 13400 BCE || -3.0 || See {{w|Origin of the domestic dog}}. This timeline event is not quite accurate. The first dogs differentiated from {{w|Gray wolf|wolves}} about {{w|Origin_of_the_domestic_dog#Time_of_domestication|23,500 years ago}}, but there was an event around 13500 BCE that increased the population size and may be attributable to domestication events. The early population migrating into the Americas brought domesticated dogs with them, so it must have occured beforehand within the precursor cultural populations.
|-
|| [Megan and Cueball is watching a wolf looking at them.]<br>Megan: Okay, you can live in our homes and we’ll feed you, but we’ll still get mad if you poop on the floor. <br> Wolf: Deal. <br> Cueball: And we get to breed you to be tiny and dress you in little costumes. <br>Wolf: …Wait. || 13100 BCE || -2.8 || Megan is making a deal with the wolf that it can eat and sleep with the humans as long as they can yell at it for pooping indoor. This sounds like a sweet deal for the wolf until Cueball mentions that they will {{w|Dog breeding|breed}} it to be {{w|Chihuahua (dog)|very small}} and then dress it up in small {{w|Dog's fashion|costumes}}. The wolf says wait, but it is already too late...

|-
| rowspan="2"| 13000 <small>BCE</small>
| {{w|Woolly Rhino}} goes extinct || 12900 BCE || -2.7 || Mainland woolly rhinos died in the {{w|Quaternary extinction event}}, but a small island population survived until {{w|Woolly_rhinoceros#Extinction|around 8000 BCE}}. Woolly rhinos likely became extinct in part due to {{w|Holocene extinction|over-hunting}}. Randall's choice of species on this chart seems to focus on animals that were greatly affected by humans, for good or ill.
|-
| {{w|Oregon}} is scoured by huge floods as glacial dams burst and lakes of meltwater flow to the sea || 12600 BCE || -2.2 || This is a reference to the {{w|Missoula Floods}} several cataclysmic floods that swept periodically across eastern {{w|Washington}} and down the {{w|Columbia River Gorge}} flooding much of eastern Washington and the {{w|Willamette Valley}} in western Oregon at the end of the last ice age. During the last {{w|deglaciation}} ice dams formed then burst several times between 13,000 and 11,000 BCE. 

|-
| rowspan="1"| 12500 <small>BCE</small>
| Ice sheets withdraw from Chicago || 12200 BCE || -1.8 || The next step towards the Canadian border, after they left New York at 13,600 BCE.

|-
| rowspan="1"| 12000 <small>BCE</small>
| Humans settle {{w|Abu Hureyra}} in {{w|Syria}} || 11550 BCE || -1.6 || A well-preserved prehistoric village that existed from 11,000 to 7000 BCE (a little later than noted in the chart), allowing archaeologists to study how their culture developed.

|-
| rowspan="1"| 11500 <small>BCE</small>
| [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] <br> Temperatures start to decline, mainly in the Northern hemisphere<br> 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. <br> This cooler period is called the {{w|Younger Dryas}} || 11300 BCE || -1.6 || In the Younger Dryas, the Earth cooled by almost one degree over 1000 years. There were {{w|Outburst flood#Glacial_floods_in_North_America_.288.2C000_to_15.2C000_years_ago.29|several floods}} during the end of the ice age but the most famous is the one from {{w|Lake Agassiz}}.<br>A similar but less global effect could occur if the ice on {{w|Greenland}} melts too quickly and causes a {{w|shutdown of thermohaline circulation}}. Without the {{w|Gulf Stream}}, hot water would remain in the Gulf of Mexico and the Caribbean instead of warming the {{w|North Atlantic}} and Europe. The movie {{w|The Day After Tomorrow}} dramatized a worse-than-worst-case version of this, happening in days instead of centuries.

|-
| rowspan="1"| 11000 <small>BCE</small>
| [This is the first text to the left of the dotted curve:] <br> Humans reach {{w|Argentina}} || 10900 BCE || -1.8 || The earliest evidence of {{w|Indigenous_peoples_in_Argentina#Prehistory|humans in Argentina}}.<br>Finally the temperature graph has risen enough that there is space to write text on the left side of the curve.

|-
| rowspan="2"| 10500 <small>BCE</small>
| [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 the 1961-1990 average.] <br> Warming resumes || 10500 BCE || -1.8 || After 1000 years of slightly decreasing temperatures the warm up of Earth resumes. Over the next 3000 years the temperature increases 2.5°C, reaching a long plateau about 0.5°C above the 1961-1990 average around 7500 BCE.
|-
| Human settlements at {{w|Jericho}} ||10050 BCE || -1.4 || The {{w|Jericho#Pre-Pottery_Neolithic.2C_c._9500_BCE|first permanent settlement}} on the site of Jericho occurred around 9500 BCE, but there is evidence of {{w|Jericho#Natufian_hunter-gatherers.2C_c._10.2C000_BCE|non permanent settlement}} during this period, when cold and drought made permanent habitation in that region difficult.

|-
| rowspan="1"| 10000 <small>BCE</small>
| First development of {{w|farming}} || 9750 BCE || -1.1 || This is now called the {{w|Neolithic Revolution}}, i.e. the wide-scale transition of many human cultures from a lifestyle of {{w|Hunter-gatherer|hunting and gathering}} to one of {{w|agriculture}} and settlement. The {{w|history of agriculture}} began independently in several locations with both {{w|domestication}} of animals and the farming of different {{w|cereals}}. One of the first regions to develop farming was the {{w|Fertile Crescent}}.<br>This is also around this time that the last ice age is said to have ended.

|-
| rowspan="2"| 9500 <small>BCE</small>
| {{w|Saber-toothed cat}} goes extinct || 9200 BCE || -0.3 || Although one of these (Smilodon) was known as the {{w|saber-toothed tiger}}, most saber-toothed "cats" are not related to tigers, or any modern {{w|cats}} at all, but can be viewed as examples of convergent evolution. {{w|Smilodon}} became extinct around 8000 BCE, and the last Saber-toothed cat first became extinct around 7000 BCE, which does not fit very well with Randall's range. Indirectly humans may have caused the extinction of the Saber-toothed cat by over-hunting their {{w|megafauna}} prey, depriving the cats of food sources.

|-
| {{w|Horses}} disappear from {{w|North America}} || 9100 BCE || -0.2 || The {{w|evolution of the horse}} began millions of years ago in North America; early species {{w|Evolution_of_the_horse#Miocene_and_Pliocene:_true_equines|migrated across Beringia into Eurasia}} before their predecessors {{w|Evolution_of_the_horse#Pleistocene_extinctions|died out}}.

|-
| rowspan="4"| 9000 <small>BCE</small>
| | Last North American {{w|Pokémon}} go extinct <br> [Cueball with a spear and Megan is looking up at this last “fact”.] <br> Megan: That is not a real fact. || 8900 BCE || -0.1 || Pokemon are not real. This faux-extinction is likely a reference to the {{w|Pokémon Go}} game, which Randall spoofed in [[1705|1705: Pokémon Go]]. Virtual Pokémon now thrive throughout the entire world, and are most commonly found near [http://time.com/4443225/pokemon-go-affluent-white-neighborhoods-report/ affluent first world neighborhoods].

|-
| Temperatures reach modern levels || 8800 BCE || 0.0 || It took 11,200 years for the temperature to increase 4.3°C. It's possible that human-created effects will produce an equal change in a few hundred years.
|-
| Rising seas cut off the {{w|land bridge}} between North America and Asia || 8700 BCE || 0.1 || {{w|Beringia}} was freed of ice in 15,000 BCE. This is an example of what happens when the temperature rises and glaciers melt. Sea levels are rising again as ice on {{w|Greenland}} and {{w|Antarctica}} continues to melt.

|-
| {{w|Cattle}} domesticated || 8500 BCE || 0.2 || Cattle feature prominently in the comic [[1338: Land Mammals]].

|-
| rowspan="2"| 8500 <small>BCE</small>
| Ice sheets retreat across the Canadian border || 8400 BCE || 0.3 || Finally the glacier that began retreating from New York around 13,600 BCE succeeded in moving to Canada as it had threatened to do... 
|-
| Temperatures start to level out slightly above 1961-1990 levels || 8050 BCE || 0.4 || The next 3000 years the temperature stays within 0.2°C degree of a temperature 0.5°C above the 1961-1990 average. A very long and stable period.

|-
| rowspan="1"| 8000 <small>BCE</small>
| [The above sentence breaks over the 8000 <small>BCE</small> line. From here a maximum in temperature on the chart is reached at 0.5°C above the 1961-1990 average, which will not be overtaken until 2000 CE. It stays almost constant here until 5000 BCE where a slight cooling begins.] || 8000 BCE || 0.4 || This is the only five hundred year span with no events listed fully inside. Maybe because nothing happens with the temperature.

|-
| rowspan="2"| 7500 <small>BCE</small>
| This warm, stable period is called the {{w|Holocene Climate Optimum}} || 7400 BCE || 0.5 || Some skeptics like to say "[http://www.skepticalscience.com/10000-years-warmer.htm it was warmer in the Holocene]." This is no longer true. Global temperature began encroaching Holocene levels in 1998, and has equaled or possibly exceeded them since 2014.
|-
| {{w|Jiahu}} settled in China || 7050 BCE || 0.5 || Jiahu is another prehistoric settlement, similar to Abu Hureyra (12000 BCE), that was extensively studied by archaeologists.

|-
| rowspan="2"| 7000 <small>BCE</small>
| Final collapse of the North American ice sheet leads to rapid 2-4m sea level rise… || 6800 BCE || 0.55 || The temperature almost reached 0.6°C above the 1961-1990 average before this happened and caused the slight decrease in temperature mentioned below.
|-
| [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.] <br>…And a period of cooling in the Northern hemisphere || 6550 BCE || 0.5 || A 0.05 degree decrease in 200 years again refers to the theme of slow natural climate change.

|-
| rowspan="1"| 6500 <small>BCE</small>
| As seas rise to near their modern levels, Britain is cut off from mainland Europe || 6300 BCE || 0.45 || This is a reference to the flooding of {{w|Doggerland}}.

|-
| rowspan="1"| 6000 <small>BCE</small>
| Humans develop copper metalworking || 5600 BCE || 0.5 || The {{w|copper age}} was relatively brief before humans discovered how to make {{w|bronze}}.

|-
| rowspan="2"| 5500 <small>BCE</small>
| Massive volcanic eruption in {{w|Oregon}} creates crater lake || 5300 BCE || 0.55 || {{w|Crater Lake}} is the caldera at the top of Mount Mazama, a collapsed stratovolcano. If it erupted again, it could become a Somma volcano (see [[1714: Volcano Types]]).
|-
| {{w|Gold}} metalworking || 5050 BCE || 0.6 || The temperature peaks here at just a bit more than 0.6°C above the 1961-1990 average. It will not rise above this level until the global warming sets in in the 1900s.

|-
| rowspan="2"| 5000 <small>BCE</small>
| {{w|Invention of the wheel}} || 4900 BCE || 0.6 || Wheels are one of the most important inventions of humanity. They feature in many xkcd comics, such as [[1075: Warning]].
|-
| [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 above the 1961-1990 average until 1000 BCE where a stable plateau is reached around the 1961-1990 average.] <br> Earth begins to cool slowly mainly due to regular cycles in its orbit || 4800 BCE || 0.5 || Again a reference to the {{w|Milankovitch cycles}} mentioned in detail at 18,600 BCE. Here they cause a cooling rather than a heating as they did back then.

|-
| rowspan="3"| 4500 <small>BCE</small>
| {{w|Proto-Indo-European language}} develops || 4400 BCE || 0.5 || Most of the languages in Europe, the Middle East, and India share a surprising number of common roots. PIE is the theoretical ancestor from which they descend. Randall mentions this language family in many comics, such as [[890: Etymology]].
|-
| [To the right of the curve Ponytail holds up a hand towards Cueball.]<br> Ponytail: Let’s make our language heavily inflected, so future students have to memorize a zillion verb endings!<br> Cueball: Okay! || 4400 BCE || 0.5 || Ponytail gets the idea to develop the language heavily inflected to make it difficult to remember all the verb endings for future students and Cueball is okay with that. This is a direct reference to the comic [[1709: Inflection]].
|-
| Permanent settlements in the {{w|fertile crescent}} || 4200 BCE || 0.5 || The Fertile Crescent is one of those things you're supposed to remember from grade school. A lot of historic milestones happened there, such as the pyramids of Giza, the code of Hammurabi, and the Abrahamic religions.

|-
| rowspan="2"| 4000 <small>BCE</small>
| Horses domesticated || 3950 BCE || 0.5 || Horse riding was the greatest advance in land travel until the invention of engines. Horses appear in many xkcd comics, such as [[936: Password Strength]].
|-
| {{w|Minoan culture}} arises on Crete || 3700 BCE || 0.5 || Minoan culture invented many strange and wonderful things, such as the Labyrinth at Knossos and {{w|Bull-leaping}}.

|-
| rowspan="4"| 3500 <small>BCE</small>
| {{w|Egyptian mummification}} || 3500 BCE || 0.5 || xkcd has discussed mummification in {{what if|134|What If? 134: Space Burial}}.
|-
| Rise of the {{w|Indus Valley civilization}} || 3300 BCE || 0.5 || The largest bronze-age civilization.
|-
| Invention of {{w|writing}} in {{w|Sumer}} “{{w|prehistory}}” ends, “{{w|history}}” begins || 3200 BCE || 0.5 || Our knowledge of prehistoric events must rely on digging up artifacts and making inferences. After this time, it became possible to find descriptions of past people and events, which is the definition of history. (Old guy in Sumer: Kids these days with their new-fangled stone tablets, instead of using their memory...)
|-
| Earliest human whose name we know (Pharaoh {{w|Iry-Hor}} in Egypt) || 3100 BCE || 0.5 || The first named person we know of today! This was also mentioned as a "cool fact" in the title text of [[1355: Airplane Message]].
|-
| rowspan="5"| 3000 <small>BCE</small>
| {{w|Three Sovereigns and Five Emperors}} period in China || 2800 BCE || 0.4 || The temperature has finally dropped below 0.5°C above the 1961-1990 average after almost 2000 years of cooling from 0.6°C above the 1961-1990 average.
|-
| {{w|Gilgamesh}} || 2700 BCE || 0.4 || Gilgamesh was probably a Sumerian king whose tales were exaggerated into mythology.
|-
| {{w|Imhotep}} || 2600 BCE || 0.4 || Imhotep was not a pharaoh, but a wise commoner who was elevated to chancellor, high priest, and post-mortem divinity. 
|-
| {{w|Maya civilization|Mayan}} culture emerges || 2600 BCE || 0.4 || Like the ancient Egyptians, Mayans are remembered for pyramids and {{w|logograph}}s.
|-
| {{w|Great Pyramid}} constructed || 2650 BCE || 0.4 || xkcd has discussed pyramids in [[1717: Pyramid Honey]] and {{what if|95|What If? 95: Pryamid Energy}}.

|-
| rowspan="3"| 2500 <small>BCE</small>
| {{w|Corded Ware culture}} in Europe || 2500 BCE || 0.3 || The term Corded Ware was invented by an archaeologist; no civilization actually called themselves that.
|-
| [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.] <br> {{w|Stonehenge}} completed || 2200 || 0.3 || This is a reference to the 1984 {{w|mockumentary}} about the fake rock band {{w|This Is Spinal Tap}}. In the movie the band wanted a giant Stonehenge prop 18 feet high, but a writing mistake gives them one that is only 18 inches.
|-
| {{w|Chariots}} developed || 2000 BCE || 0.3 || But {{w|Chariots of Fire}} came much later.

|-
| rowspan="3"| 2000 <small>BCE</small>
| {{w|Alphabetic writing}} developed in Egypt || 1750 BCE || 0.2 || Obligatory reference to xkcd [[1069: Alphabet]].
|-
| Last {{w|mammoth}}s on a tiny Siberian island go extinct || 1650 BCE || 0.2 || Many of the {{w|Pleistocene megafauna}} died in the {{w|Quaternary extinction event}}. Like the {{w|woolly rhino}} (see 12900 BCE) these animals likely became extinct in part due to {{w|Holocene extinction|humans hunting them}}, which may be why Randall included them in the chart. Most of the mammoths died out before 8000 BCE but {{w|Woolly_mammoth#Extinction|some survived in remote areas}} and the last known population died on {{w|Wrangel Island}} in the {{w|Arctic Ocean}} around 2000 BCE, slightly earlier than Randall shows here.
|-
| {{w|Minoan eruption}} || 1600 BCE || 0.2 || This volcano may have led to the downfall of Minoan civilization. 

|-
| rowspan="5"| 1500 <small>BCE</small>
| {{w|Iron smelting}} || 1400 BCE || 0.1 || The beginning of the {{w|Iron Age}}.
|-
| {{w|Olmec}} civilization develops in Central America || 1350 BCE || 0.1 || No, Maggie, not Aztec, [http://vimeo.com/34002760 Olmec].
|-
| [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]<br> Setting of the ''{{w|Iliad}}'' and the ''{{w|Odyssey}}''<br> Text on horse: Not a trap || 1250 BCE || 0.1 || A reference to the {{w|Trojan War}} qua the drawing of the {{w|Trojan Horse}}. The horse was a big trap letting the soldiers hidden inside it into {{w|Troy}}. This explains why it has ''Not a trap'' written on it. Else they would not have taken the giant wooden horse present from their sworn enemies into their city just like that... Note that the Trojan horse isn't mentioned in the Iliad, and only recalled in passing by the characters in the Odyssey.
|-
| Invasion of the {{w|Sea peoples}}* <br>* A real thing || 1200 BCE || 0.1 || {{w|Mermaid#One_Thousand_and_One_Nights|Sea people}} might sound like a reference to mythical {{w|mermaid}}s, so Randall feels the need to footnote that this event was ''a real thing'' (as opposed to his Pokémon reference, which he notes is ''not a real fact''). The sea peoples were a seafaring confederation of groups known to have attacked ancient Egypt around this time.
|-
| {{w|Polynesians}} explore the Pacific Ocean || 1000 BCE || 0.1 || {{w|Polynesian navigation}} was surprisingly widespread.

|-
| rowspan="8"| 1000 <small>BCE</small>
| [From 1000 BBC to 1000 CE the temperature is stable and very close to the 1961-1990 average.] || 1000 BCE || 0.1 || The temperature has fallen from the Holocene Optimum by half a degree to just a bit above the the 1961-1990 average. It will stay in this range for the next 2000 years.
|-
| {{w|Solomon}} || 1000 BCE || 0.1 || Solomon may have been a real historical king, but he probably did not threaten to chop a baby in half.
|-
| {{w|Iliad}} and {{w|Odyssey}} composed || 900 BCE || 0.1 || These classic myths were written more than 300 years after their supposed events. Archaeologists believe the city of {{w|Troy}} existed (and was destroyed by war around the right time period), but characters like Helen, Odysseus, and Achilles did not.
|- 
| Rise of {{w|Greek city-states}} || 800 BCE || 0.1 || This is ''Sparta'', along with Athens and several others.
|-
| {{w|Neo-Assyrian Empire}} || 800 BCE || 0.1 || Hi, you may remember us from such kings as Adad-nirari and Sennacherib.
|-
| {{w|Ancient Olympic Games|First Olympics}} || 750 BCE || 0.1 || The first of the ancient Olympic Games is traditionally dated to 776 BC.
|-
| {{w|Zapotec civilization|Zapotec}} writing in modern Mexico || 600 BCE || 0.0 || Another Central American culture that fell to the Spanish invasion.
|-
| {{w|Confucius}} || 550 BCE || 0.0 || "He who knows all the answers has not been asked all the questions."

|-
| rowspan="10"| 500 <small>BCE</small>
| The stuff in the {{w|300 (film)|movie ''300''}}, but regular speed and with more clothing || 450 BCE || 0.0 || A reference to the {{w|Battle of Thermopylae}} by comparison with the 2007 movie ''300'' about this battle. The real Spartans wore armor, and real humans don't [http://www.google.com/search?q=300+slow-motion fly through the air in slow motion when struck].
|-
| {{w|Buddha}} || 450 BCE || 0.0 || Randall also mentions other religious figures like {{w|Jesus}} and {{w|Muhammad}}.
|-
| {{w|Nazca Lines}} || 350 BCE || 0.0 || These huge ancient drawings are difficult to see from ground level, leading some people to believe that they were intended for aliens.
|-
| {{w|Alexander the Great}} || 350 BCE || 0.0 || One of the most successful conquerors of the iron age, known for supposedly cutting the {{w|Gordian Knot}}.
|-
| {{w|Mayan hieroglyphics}} || 250 BCE || 0.0 || The {{w|Maya Calendar}} was probably created hundreds of years later.
|-
| {{w|Ashoka the Great}} || 250 BCE || 0.0 || The {{w|Edicts of Ashoka}} proselytized Buddhism across the continent.
|-
| {{w|Paper}} invented || 200 BCE || 0.0 || A significant step up from stone tablets or even papyrus.
|-
| {{w|Asterix}} || 100 BCE || 0.0 || Fictional main character in ''The Adventures of Asterix'', a comic series set around 50 BCE when {{w|Julius Caesar}} conquered {{w|Gaul}}.
|-
| {{w| Teotihuacan|Teotihuacán}} metropolis || 100 BCE || 0.0 || Another ancient city much beloved by archaeologists, even though they don't know who built it.
|-
| {{w|Julius Caesar}} || 50 BCE || 0.0 || Aside from being a conqueror, dictator, and deity, Julius had a big impact on {{w|Julian Calendar|calendars}}. The month of Quintilis was renamed July to honor him, and he was famously assassinated on the ides (middle day) of March.
|-

|-
| rowspan="8"|1 <small>BCE</small><br>1 <small>CE</small>
| [Instead of a zero, there are two numbers for each of the two scales before (1 BCE) and after Christ (1 CE)] || 0 CE || -0.1 || Originally the year range went directly from 1 BC to 1 AD. The year zero has since been added for ease of mathematical and astronomical calculations.
|-
| {{w|Roman Empire}} || 1 CE || -0.1 || Julius never held the title "Emperor"; his adoptive son Augustus was the first to do so.
|-
| {{w|Jesus}} || 1 CE || -0.1 || Randall also mentions other religious figures like {{w|Buddha}} and {{w|Muhammad}}.
|-
| [To the left and erupting volcano.] <br> {{w|Pompeii}} || 100 CE || -0.1 || The volcano is {{w|Mount Vesuvius}} which exploded in 79 CE and is famous for burying everyone in the close by city Pompeii preserving peoples bodies inside the huge amount of ash that swallowed the city very rapidly. Today it has given the archeologist lots of knowledge about the culture of that time.
|-
| {{w|Three Kingdoms}} period || 250 CE || -0.1 || Not just a series of movies and video games, but an actual thing that happened in China.
|-
| {{w|Gupta empire}} || 700 CE || -0.1 || Not as great as Ashoka, but still a pretty important time in the history of India.
|-
| Various groups take turns sacking {{w|Rome}} || 550 CE || -0.1 || 500 years is a pretty successful span for an empire.
|-
| {{w|Attila the Hun}} || 550 CE || -0.1 || He probably would not mind being remembered as one of the most infamous barbarians in history.

|-
| rowspan="4"| 500 <small>CE</small>
| {{w|Muhammad}} || 600 CE || 0.0 || Randall also mentions other religious figures like {{w|Buddha}} and {{w|Jesus}}
|-
| {{w|Tang Dynasty}} || 750 CE || 0.0 || A golden age in China, responsible for the development of printing, gunpowder, and many other advances.
|-
| [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 the 1961-1990 average along this arrow.] <br> {{w|Medieval warm period}} in Europe and some northern regions (too regional to affect the global average much) || 900 CE || 0.0 || Changes in ocean currents caused various regions to warm up while others cooled.
|-
| {{w|Leif Eriksson}} || 950 CE || 0.0 || Probably the first European explorer to reach North America.

|-
| rowspan="7"| 1000 <small>CE</small>
| [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 (N, S, W, E) and a label next to it:]<br> {{w|Magnetic compass}} navigation || 1050 CE || 0.0 || It's much easier to sail to the Orient when you can orient yourself.
|-
| [The dotted curve moves to the left towards lower temperature reaching a minimum around 1650 CE of about 0.6°C below the 1961-1990 average at the {{w|Little Ice Age}}.] || 1150 CE || -0.1 || This less than half a degree drop in temperature over 500 years was enough to cause the "Little Ice Age" which resulted in extended ice coverage in the winters in instance Europe. See more below at the entry for the Little Ice Age.
|-
| {{w|Genghis Khan}} || 1200 CE || -0.2 || Mongol emperor. {{w|Gengar}} is not named after him, but [http://bulbapedia.bulbagarden.net/wiki/Kangaskhan_(Pokémon) Kangaskhan] and [http://awoiaf.westeros.org/index.php/Khal the Khals] are.
|-
| {{w|Zheng He}}’s fleet explores Asia and Africa || 1400 CE || -0.3 || He explored farther than European contemporaries like Dias or de Gama.
|-
| {{w|Aztec Empire|Aztec Alliance}} || 1400 CE || -0.3 || Aztec dominance only lasted a century until Cortes arrived, but their cultural legacy is indisputable.
|-
| {{w|Printing press}} || 1450 CE || -0.3 || {{w|Johannes Gutenburg}} ushered in the {{w|Age of Enlightenment}}.
|-
| {{w|Christopher Columbus|Columbus}} || 1490 CE || -0.3 || The time given here references when Christopher Columbus reached the {{w|Americas|New World}} in 1492. The five events around 1500 CE lies very close together but it fits with Columbus fitted in just before 1500.

|-
| rowspan="2"| 1500 <small>CE</small>
| {{w|European Renaissance}} || 1500 CE || -0.3 || From here on, the chart has labels for each 100 year increment instead of 500, but the scale stays the same. Important events happens so much faster in these last five hundred years, there isn't enough space to write all of them, so Randall has had to be selective. He includes {{w|Isaac Newton}} but leaves out {{w|Albert Einstein}}, includes {{w|airplane}}s but leaves out {{w|car}}s, etc.
|-
| {{w|Shakespeare}} || 1600 CE || -0.4 || xkcd references Shakespeare many times, such as [[79: Iambic Pentameter]] and [[1026: Compare and Contrast]].

|-
| rowspan="2"| 1600 
| {{w|Isaac Newton|Newton}} || 1650 CE || -0.4 || Isaac Newton appears in various xkcd comics, such as [[626: Newton and Leibniz]].
|-
| [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. This is the coldest it has been since 9500 BCE. It is labeled:]<br> ”{{w|Little Ice Age}}” || 1650 CE || -0.4 || This was not a true geologic Ice Age, just a slightly chilly period when the temperature fell a fraction of a degree,  but still colder than it had been through 11,000 years of human civilization. In Europe the winters were so cold that the river {{w|Thames}} {{w|Little_Ice_Age#Europe|froze over}} hard enough to hold {{w|River Thames frost fairs}} between 1607 and 1814. And in 1658 {{w|Sweden}} crossed the {{w|Danish Straits}} on foot to invade {{w|Copenhagen}} in the {{w|March Across the Belts}}. It was only possible due to the harsh winters of the Little Ice Age, demonstrating how much half a degree of climate change can mean.

|-
| rowspan="2"| 1700
| {{w|Steam engines}} || 1750 CE || -0.4 || The {{w|Age of Steam}} heralded the upsurge of human CO<sub>2</sub> emissions.
|-
| {{w|United States Declaration of Independence|Unites States Independence}} || 1770 CE || -0.3 || On July 4, 1776.

|-
| rowspan="3"| 1800
| {{w|Industrial Revolution}} || 1825 CE || -0.3 || Not to be confused with {{w|Industrial music}} such as Nine Inch Nails.
|-
| {{w|Electrical telegraph|Telegraphs}} || 1830 CE || -0.3 || [https://youtu.be/gEGQUgWBQL4?t=56s -. --- .-- --..-- / - .... . / -- --- - .... . .-. / --- ..-. / ... .- -- ..- . .-.. / -- --- .-. ... . / .- .-.. .-- .- -.-- ... / ... . -. - / - .... . / .-.. .- -.. / --- ..- - / --- -. / .- / .... --- .-. ... .]
|-
| [After this the dotted curve becomes solid.] || 1850 CE || -0.3 || From 1850 weather records became sufficiently accurate and widespread to greatly improve the precision of climate measurements. Hence the curve stops being an estimate and thus also stops being a dotted curve and becomes solid.

|-
| rowspan="6"| 1900
| {{w|Airplane}}s || 1900 CE || -0.3 || xkcd discusses airplanes many times, such as [[726: Seat Selection]] and {{what if|30|30: Interplanetary Cessna}}.
|-
| {{w|World Wars}} || 1930 CE || -0.2 || Likewise, there are many xkcds on this topic, such as [[261: Regarding Mussolini]] and {{what if|100|100: WWII Films}}.
|-
| [The solid line takes a step to the right close to the 1961-1990 average. Over the rest of the 1900s it moves closer to the 1961-1990 average, crossing it before 2000 where it almost reaches the maximum temperature of 0.5 °C above the 1961-1990 average from earlier in 8000 BCE.] || 1940 CE || -0.2 || This is what the previous 14000 pixels of comic has been leading up to. After a laborious 20 millennia of gradual and meandering climate change, it should be clear that a full degree of warming in a single century is unprecedented in human history, and very unlikely to be natural variation.
|-
| {{w|Fossil fuel}} CO<sub>2</sub> emissions start rapidly increasing || 1950 CE || -0.1 || The infamous [http://www.skepticalscience.com/Hockey-stick-or-hockey-league.html "hockey stick"] starts around here.
|-
| {{w|Nuclear weapons}} || 1950 CE || -0.1 || The Working Group on the 'Anthropocene' suggests dating the {{w|Anthropocene}} epoch from ~1950. The week after this comic [[1736: Manhattan Project]] with a mushroom cloud was released.
|-
| {{w|Internet}} || 1980 CE || 0.1 || The origin of the internet dates back to 1960 but it began growing rapidly in 1980. By placing the invention of the {{w|internet}} at 1980 in the chart, just where the temperature curve starts its most rapid increase, Randall uses this [[552: Correlation|correlation]] to humorously imply that the internet caused the rise in temperature.<br> This is also where the temperature crosses the 1961-1990 average, which has to happen somewhere due to the {{w|Intermediate Value Theorem}}.

|-
| rowspan="2"| 2000
| {{w|Northwest Passage}} opens || 2000 CE || 0.4 || This was dramatic evidence that the climate had changed. When global warming removes enough sea ice to create shipping routes that never existed before, then it is clear to people that ''something'' is changing, even if they disregard who/what is responsible for the change.
|-
|[From here to present day the solid line increases rapidly and in 2016, present day, is almost reaches 1°C above the 1961-1990 average, with about 0.8°C above the 1961-1990 average.] || 2016 CE || 0.8 || '''Notice''': [http://www.skepticalscience.com/argument.php?a=11&p=2 Warming did not stop] in 1998.

|-
| rowspan="3"| 2016
| | Present day || 2016 CE || 0.8 || Today, just after the two hottest months ever measured since 1850 had ended (July and August 2016), this comic was released with the message displayed very clearly here below. Act now or fry...
|-
| [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.] || 2016 CE || 0.8 || Here stops the data and the projection into the future begins so the curve again becomes dotted. Three different scenarios are depicted.
|-
|The first curve bending down before the others, and thus to the right of the other two reaches about 1.2°C above the 1961-1990 average and then goes straight down and stops at the 2100 line. An arrow points to it from the left and a label is written partly before and the rest after the 2100 line to the left of the curve:] <br>Best-case scenario assuming immediate massive action to limit emissions || 2100 CE || 1.2 || If humanity does all in its power to stop global warming we might be able to halt the global warming already before 2050 keeping the maximum temperature to just 1.2°C above the 1961-1990 average. Only 0.4°C above today's temperature.  (Note that this is not, in fact, the absolute best-case scenario, as it assumes that no new greenhouse gasses are either added to or removed from the atmosphere in the future; the temperature rise could be kept to an even lower level if some or all of the already-emitted greenhouse gasses were removed from the atmosphere.)

|-
| rowspan="2"| 2100
| [The middle curve bends a little down after reaching 1.3°C above the 1961-1990 average, and then continues this path reaching 2°C above the 1961-1990 average in 2100. An arrow point from below to it and a label is written below the curve and below 2100 line:] <br> Optimistic scenario|| 2100 CE || 2.0 || If all the current realistic preventions are implemented, which might not be so realistic, then we may not even stop the warming but slow it down so we "only" reach 2°C above the 1961-1990 average in 2100 CE but it would not stop there. This is half the temperature change experienced since the ice age, but the other way. This was directly referenced in the title text of [[1379: 4.5 Degrees]]: ''That's only HALF an ice age unit (IAU), which is probably no big deal.''
|-
| [The last line continues along the path from the last 16 years of the solid line reaching 4.2°C above the 1961-1990 average at 2100, almost as far on the other side of the 1961-1990 average in 150 years as it took 14,000 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:] <br> Current Path || 2100 CE || 4.2 || In this last scary scenario Randall assumes the temperature keeps rising steadily by extrapolating along the slope of the last two to three years. Randall has warned about the hazards of [[Extrapolating]], but this line is in fact [http://www.skepticalscience.com/climate-best-to-worst-case-scenarios.html below the worst case predictions]. If this comes true we will reach a temperature increase taking us from the 1961-1990 average and in just 125 years to 4.2°C above this average. That is just as far above this average in that short time span as the ice age temperature was below. And it took more than 11,000 years for nature to reach such an increase. Randall already contemplated what this would be like in the +1 ice age unit (IAU) panel of [[1379: 4.5 Degrees]] two years ago, as well as in [[164: Playing Devil's Advocate to Win]] almost 10 years ago. He may get to ''enjoy quite a ride'' as he "wished" for back then. 

There is no reason to assume the temperature will not keep rising past 2100 CE, so the {{w|Cretaceous Thermal Maximum|"Hothouse Earth"}} of the early {{w|Cretaceous period}} mentioned in the 4.5 degree comics +2 IAU panel might come to pass in future centuries if we continue on our current path. On the bright side, modern civilization might collapse if this trend keeps up, which would drastically cut our releases of carbon dioxide and other greenhouse gasses into the atmosphere. But then again, positive feedback from methane in melting {{w|permafrost}} might take over... Good luck Earth.
|}

===Sources===
The image attributes climate data sources as "Shakun et al. (2012), Marcott et al. (2013), Annan and Hargreaves (2013), HadCRUT4, IPCC":
* Shakun, Jeremy D.; Clark, Peter U.; He, Feng; Marcott, Shaun A.; Mix, Alan C.; Liu, Zhengyu; Otto-Bliesner, Bette; Schmittner, Andreas; Bard, Edouard (2012-04-04). [https://web.archive.org/web/20160520043848/http://www.atm.damtp.cam.ac.uk/mcintyre/shakun-co2-temp-lag-nat12.pdf "Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation"] (PDF). ''Nature''. '''484''' (7392): 49–54. doi:[https://doi.org/10.1038%2Fnature10915 10.1038/nature10915]. ISSN [https://www.worldcat.org/issn/1476-4687 1476-4687]. Archived from [https://www.nature.com/articles/nature10915 the original] on 2016-05-20.
* Marcott, Shaun A.; Shakun, Jeremy D.; Clark, Peter U.; Mix, Alan C. (2013-03-08). [https://web.archive.org/web/20130412021608/https://content.csbs.utah.edu/~mli/Economics%207004/Marcott_Global%20Temperature%20Reconstructed.pdf "A Reconstruction of Regional and Global Temperature for the Past 11,300 Years"] (PDF). ''Science''. doi:[https://doi.org/10.1126%2Fscience.1228026 10.1126/science.1228026]. Archived from [https://www.science.org/doi/abs/10.1126/science.1228026 the original] on 2013-04-12.
* Annan, J. D.; Hargreaves, J. C. (2013-02-13). [https://web.archive.org/web/20200728042751/https://cp.copernicus.org/articles/9/367/2013/cp-9-367-2013.pdf "A new global reconstruction of temperature changes at the Last Glacial Maximum"] (PDF). ''Climate of the Past''. '''9''' (1): 367–376. doi:[https://doi.org/10.5194%2Fcp-9-367-2013 10.5194/cp-9-367-2013]. ISSN [https://www.worldcat.org/issn/1814-9324 1814-9324]. Archived from [https://cp.copernicus.org/articles/9/367/2013/ the original] on 2020-07-28.
* {{w|HadCRUT|HadCRUT (Hadley Centre/Climatic Research Unit Temperature)}} - [http://www.metoffice.gov.uk/hadobs/hadcrut4/ Official site] 
* {{w|Intergovernmental Panel on Climate Change}} - [http://www.ipcc.ch/ Official site]

==Transcript==
'''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|trivia section]].
:[A large heading, followed by a sub-caption. Below that two lines with a statement in between:]
:<big>A timeline of Earth’s average temperature</big>
: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'''
: <small>Compared to the 1961-1990 average</small>
: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:]
: <font color="gray">Source: Shakun et. al. (2012) , Marcott et. al. (2013), Annan and Hargreaves (2013) , HadCRUT<sub>4</sub>, IPCC </font>

:[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 <small>BCE</small>
::[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<sup>th</sup> 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 <small>BCE</small>
::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 <small>BCE</small>
::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<sup>2</sup> at 60°N
:::550
:::500
:::450

:18500 <small>BCE</small>
::[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 <small>BCE</small>
::…And the ice sheets start to melt.

:17500 <small>BCE</small>
::Temperatures have been creeping upward, but around this point, CO<sub>2</sub> levels start to climb…

:17000 <small>BCE</small>
::…And then the warming speeds up.

:16500 <small>BCE</small>
::[Cueball is standing with a spear just the right of the graph talking to a rabbit.]
::Cueball: Still pretty cold.

:16000 <small>BCE</small>
::[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 <small>BCE</small>
::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 <small>BCE</small>
::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 <small>BCE</small>
::[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 <small>BCE</small>
::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 <small>BCE</small>
::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 <small>BCE</small>
::[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 <small>BCE</small>
::Ice sheets withdraw from Chicago

:12000 <small>BCE</small>
::Humans settle Abu Hureyra in Syria

:11500 <small>BCE</small>
::[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 <small>BCE</small>
::[This is the first text to the left of the dotted curve:]
::Humans reach Argentina

:10500 <small>BCE</small>
::[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 <small>BCE</small>
::First development of farming

:9500 <small>BCE</small>
::Saber-toothed cat goes extinct
::[To the left:]
::Horses disappear from North America

:9000 <small>BCE</small>
::[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 <small>BCE</small>
::Ice sheets retreat across the Canadian border
::Temperatures start to level out slightly above 1961-1990 levels

:8000 <small>BCE</small>
::[The above sentence breaks over the 8000 <small>BCE</small> 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 <small>BCE</small>
::[To the left:]
::This warm, stable period is called the Holocene Climate Optimum
::[To the left:]
::Jiahu settled in China

:7000 <small>BCE</small>
::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 <small>BCE</small>
::[To the left:]
::As seas rise to near their modern levels, Britain is cut off from mainland Europe

:6000 <small>BCE</small>
::Humans develop copper metalworking

:5500 <small>BCE</small>
::[To the left:]
::Massive volcanic eruption in Oregon creates crater lake
::Gold metalworking

:5000 <small>BCE</small>
::[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 <small>BCE</small>
::[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 <small>BCE</small>
::Horses domesticated
::[To the left:]
::Minoan culture arises on Crete

:3500 <small>BCE</small>
::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
::<small>(Pharaoh Iry-Hor in Egypt)</small>

:3000 <small>BCE</small>
::''Three Sovereigns and five emperors'' period in China
::Gilgamesh
::[To the left:]
::Imhotep
::Mayan culture emerges
::[To the left:]
::Great Pyramid constructed

:2500 <small>BCE</small>
::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 <small>BCE</small>
::[To the left:]
::Alphabetic writing developed in Egypt
::Last mammoths on a tiny Siberian island go extinct
::[To the left:]
::Minoan eruption

:1500 <small>BCE</small>
::[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*
::<small>* A real thing</small>
::Polynesians explore the Pacific Ocean

:1000 <small>BCE</small>
::[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 <small>BCE</small>
::[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 <small>BCE</small>
:1 <small>CE</small>
::[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 <small>CE</small>
::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 <small>CE</small>
::[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:]
:::<small>N</small>
:::<small>W E</small>
:::<small>S</small>
:::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 <small>CE</small>
::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<sub>2</sub> 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

==Trivia==
*There have been several ''[[:Category:Large drawings|large drawings]]'' in the history of xkcd, some of which are bigger than this one (for instance [[1110: Click and Drag]]). 
**Among those that can be viewed in one go, without downloading a larger file or moving around, this is by far the longest.
**The next longest is probably [[482: Height]].
*The timeline starts at 20,000 BCE (22,000 years ago) and ends at 2100 CE, thus covering 22,100 years. 
*There are several spelling mistakes. 
**Most obvious is the second time Randall wrote the word "Iliad," because he just spelled it correctly at 1500 BCE and then spelled it ''Illiad'' at 1000 BCE with two Ls.
**Attila the Hun was initially misspelt ''Atilla the Hun'' with ''one'' T and ''two'' Ls, but this was corrected at some point.
**Genghis Khan is misspelt as ''Ghengis Khan'' (a common error).
**Pokémon is spelled ''Pokemon'', but then again, that is not so strange for Randall (see [[1647: Diacritics]]). Despite that, he usually spells it correctly, as in [[1705|1705: Pokémon Go]].
**Note that the fact that woolly rhinoceros becomes ''Wooly rhino'' with only one l is not a spelling mistake but an alternative spelling of the word.
*The following notable facts are absent
**1850: methodical temperature record begins. However, this fact is indirectly indicated when the temperature curve becomes solid around 1850 and until present day.
**The entire swing period between 20 and 200 thousand years prior to now would depict temperature swings with increasing frequency and amplitude (ref geological record). But of course, this could not be included in a comic that only goes back to 20,000 BCE. 
**During much of the 300 million years prior to that, the Earth was significantly warmer than now. However, the data's temporal precision decreases with age; seemingly abrupt changes millions of years ago might have happened over centuries or millennia. Hence, the older data is not usable to compare rates of change.

===Popularity of comic===
This comic became popular with a much broader audience than most xkcd comics. It was discussed admiringly by news sites such as [http://www.popsci.com/xkcd-earth-average-temperature-timeline Popular Science], [http://reason.com/blog/2016/09/14/send-around-this-xkcd-climate-change-web Reason], [http://www.slate.com/blogs/bad_astronomy/2016/09/13/xkcd_takes_on_global_warming.html Slate], [http://www.smithsonianmag.com/smart-news/new-comic-masterfully-shows-how-climate-has-changed-through-time-180960451/ Smithsonian], [http://www.forbes.com/sites/ericmack/2016/09/13/heres-22000-years-of-climate-changes-in-a-single-comic/ Forbes], [https://www.vox.com/2016/9/12/12891814/climate-change-xkcd-graphic Vox], [https://www.npr.org/sections/goatsandsoda/2016/09/14/493925781/epic-climate-cartoon-goes-viral-but-it-has-one-key-problem NPR], [https://qz.com/780391/xkcd-tells-the-entire-history-of-humanity-and-climate-change-in-one-cartoon-chart/ Quartz], [https://www.sciencealert.com/why-4-5-million-years-of-fluctuating-global-temperatures-can-t-explain-climate-change-today Science Alert] and [https://www.climatecentral.org/news/climate-change-xkcd-comic-20696 Climate Central]. It was promoted by famous individuals such as [https://twitter.com/elonmusk/status/775632728548970500 Elon Musk] and even [https://twitter.com/unfccc/status/776129715799224320 twitted by the UN council on Climate Change], and obviously hated on by vocal {{rw|climate_change|climate change deniers}} and {{rw|crank|cranks}} such as [https://www.reddit.com/r/dataisbeautiful/comments/53poul/josh_takes_on_xkcds_climate_timeline/ Anthony Watts]<sup><small>{{rw|Anthony_Watts|debunked}}</small></sup> and [http://joannenova.com.au/2016/09/how-to-make-climate-graphs-look-scary-a-reply-to-xkcd/ Joanne Nova]<sup><small>{{rw|Joanne_Nova|debunked}}</small></sup>

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]] [https://www.scpr.org/news/2016/09/15/64670/epic-climate-cartoon-goes-viral-but-it-has-one-key/#comment-2900724860 may be more correct than he realises]. Calling that process computer modeling stretches the meaning of the phrase. For more {{rw|rationalist}} critique of this chart not driven by the agenda of pushing {{rw|pseudoscientific}} beliefs which are against the worldwide consensus, see [https://www.climatecentral.org/news/climate-change-xkcd-comic-20696 t][https://reason.com/2016/09/14/send-around-this-xkcd-climate-change-web/ h][https://www.npr.org/sections/goatsandsoda/2016/09/14/493925781/epic-climate-cartoon-goes-viral-but-it-has-one-key-problem i][https://www.scpr.org/news/2016/09/15/64670/epic-climate-cartoon-goes-viral-but-it-has-one-key/ s] and most insightfully, [https://scienceblogs.com/gregladen/2016/09/13/everybody-always-gets-this-wrong-even-smart-people this].

*Due to increased interest, Randall decided to push the release of the next comic [[1733: Solar Spectrum]] one day back for a rare [[:Category:Thursday comics|Thursday release]] instead of the scheduled [[:Category:Wednesday comics|Wednesday release]]. 
**He [http://web.archive.org/web/20160915101125/http://xkcd.com/ noted this] above [[:image:1732_Earth_Temperature_Timeline_header_text_changed_for_all_comics.png|all the comics]] in the [[:image:1732_Earth_Temperature_Timeline_header_text_changed.png|header text on xkcd]]:
::''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 [http://web.archive.org/web/20160912181546/https://xkcd.com/ normal heading] with the release day of xkcd was shown.
:*This was (of course) still there Tuesday the [http://web.archive.org/web/20160913231501/http://xkcd.com/ day after] the release, because it was first on Wednesday there were reason to note the delay.
:*It stayed in place even [[:image:1732_Earth_Temperature_Timeline_header_text_changed_also_when_next_comic_was_released.png|for some time after]] the "Wednesday" comic was released on Thursday, but was [http://web.archive.org/web/20160915154605/http://xkcd.com/ then removed] before [[:image:1732_Earth_Temperature_Timeline_header_text_back_to_normal_shortly_after_next_comic_was_released.png|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 [[1734:_Reductionism#Trivia|this trivia item]] from the Friday comic.
*On 2019-03-01, this comic became one of the six [[Design of xkcd.com|footer]] comics.
==== Removal of warning and footnote ====
*This comic's popularity was possibly the reason that both the more-than-10-year-old [[xkcd warning]] as well as the [[footnote#Original_footnote|original footnote]] was [[footnote#Removal_of_original_footnote|removed]] on the day of this comic's release. 
**The next footnote was added 22 days later.

{{comic discussion}}

[[Category:Comics with color]]
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[[Category:Comics featuring Megan]] 
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Hairy]]
[[Category:Comics featuring real people]] <!--Pharao/Solomon/Cesar, Jesus? etc -->
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[[Category:Music]] <!-- People with Guitars around Stone henge -->
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