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.
}}

==Explanation==
{{TOC}} 
{{incomplete|[[#Table of all elements|Table for explanations]] now ready to be filled out. Please remove this tag only when everything is explained.}}
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 is a direct, but much more thorough, follow up on the previous global warming comic: [[1379: 4.5 Degrees]].

This comic shows that while temperature changes have indeed occurred before, the speed of the current temperature rise is much, much faster than those seen (actually: estimated) in the previous thousands of years. It seemed to touch on something in peoples consciousness, because it 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. 

This comic is a [[:Category:Timelines|timeline]] on how the temperature has changed since 20,000 BCE (Before {{w|Common Era}}) to the present day and extrapolated 84 years on from present day of the release of the comic (2016) to 2100 {{w|Common Era|CE}} depending on the choice of actions to stop CO₂ emission that is taken now or never. It is meant to contrast the slow-paced natural changes with the rapid temperature rise in the recent years. The effect is achieved by forcing the reader to scroll endlessly through slow, building-up changes and then face them with an almost instantaneous, quick rise towards the end. The temperature curve is a dotted line most of the time, but from about 1850 to present day (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 curve is also dotted as this is predictions. And here there are even three possible outcomes depending on how seriously politicians and other influential people (and the population of Earth) take 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 [[#Jokes in the comic|list below]]). He even included one at the base of the comic where the serious human caused temperature increase is at display. By placing the invention of the {{w|internet}} at 1980 in the chart, just where the temperature curve starts its most rapid increase, he humorously implies that the internet caused the rise in temperature. Randall has before been after incidents where cause and effects like this has been used without any proof that it was not a coincidence. 

Below in the [[#Table of all elements|table]] each entry will be noted and explained (in time). This is one of the comics where Randall cites his [[#Sources|sources]] like he did for one of his other very large comics [[980: Money]].

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. A related joke was used recently in [[1693: Oxidation]].

===Jokes in the comic===
*Above the joke about the internet causing the global warming is mentioned.
*Other "silly" jokes included in the comic are:
**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!'' A joke on the typical saying by US citizens that are unhappy with changes in their country, as a kind of protest. According to the chart the glacier first retreated over the Canadian border around 8400 BCE more than 5000 years later.
**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 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...
**The {{w|Pokémon}} reference at 9000 BCE about them going extinct in North America (although Megan does proclaim that this is not a real fact). As the writing stated that ''Pokémon go extinct'' this can also be seen as a reference to the recently released {{w|Pokémon Go}} game and hence also the recent comic [[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. A direct reference to the recent 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 bands 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 foot note. 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 around this time.
**At 450 BCE a reference to the {{w|Battle of Thermopylae}} (also known as 300 Spartans) he references this by comparing the event with the 2007 movie ''{{w|300 (film)|300}}'' about this battle. But notes that in the real world the fighting of course occurred at regular speed and that they probably had more clothing on in the real world than in the fictionalized action movie.
*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 celcius 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 to the climate average from 1961-1990, rather than an absolute temperature reading. As a rule {{w|climate}} changes are compared with a 30 year interval, and {{w|Climate#Definition|recently}} the 1961-1990 average was chosen for convenience as the "normal" to compare temperature changes with, but any other choice of baseline would show the exact same changes. The timeline staring at 20,000 BCE fits with Wikipedia's article on {{w|Last glacial period}} (or the last ice age) stating that the  the maximum extent of {{w|glaciation}} was approximately 22,000 years ago. However, in the article on the {{w|Last Glacial Maximum}} it states that this maximum occurred 24,500 BCE 4,500 years before the other article (even though they link to each other).
|-

| {{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. A guy with a white {{w|knit cap}} is seen walking in a snowy landscape. The skyline of Boston is shown under a half a mile of ice.] || 19700 BCE || -4.3 || The Boston image is directly taken from [[1225: Ice Sheets]] about the ice age glacier coverage and the guy with the white knit cap could be the guy from [[1321: Cold]] also about global warming. It shows what a difference 4 degree in global temperature means (massive effect), as opposed to what four degree means on a daily weather wise scale (nothing!). [[Randall]] lives in Boston. It was also shown buried in ice in [[1379: 4.5 Degrees]]. Knit caps have only been used a few times in xkcd, most prominently on [[1350:_Lorenz#Knit_Cap_Girl|Knit Cap Girl]] in [[1350: Lorenz]], see her section for more details.

|-
| 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. So it becomes clear that it is not a fast warm up, especially not compared to the one we are currently experiencing and which is displayed at the very bottom of this long 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. At this time the cycles reaches a point where more sun reached the polar ice and this will begin the melting that (after thousands of years) ends the glaciation. Next to this is a chart showing the solar input, see next entry. 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 || Randall has made several comics with [[:Category:Maps|maps]]. This map is not part of a joke; it 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 is a slow process. First 4000 years later is New York free of ice (13,600 BCE in the chart), and not until after almost 10,000 years (at 8400 BCE in the chart) does the ice retreat all the way back across the Canadian border.

|-
| 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 ||The increasing CO<sub>2</sub> levels can be seen at the right end of the {{w|Carbon_dioxide_in_Earth's_atmosphere#Measuring_ancient-Earth_carbon_dioxide_concentration|green curve here}} under the Wikipedia article  about {{w|Carbon dioxide in Earth's atmosphere}}. Such natural increases may be caused by several facts. Hotter water in the ocean can dissolve less gasses and would release some of the CO<sub>2</sub> it had held during the previous colder period. Melting {{w|tundra}} that has been under {{w|permafrost}} can release gasses when the frozen plants start to decompose. Also volcanic activity could cause an increase. As can be seen on the chart nothing much happens with the temperature in spite of this increase.

|-
| 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 the temperature is still 4°C below the 1961-1990 average.

|-
| rowspan="2"| 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 below the 1961-1990 average.] || 15600 BCE || -3.9 || Megan seems to be pushing the temperature up, and this is the first time the temperature is less than 4°C below the 1961-1990 average.
|-
| [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 {{w|Beringia}} from what is now {{w|Russia}} to what is now {{w|Alaska}}, i.e. over the land bridge mentioned in the previous entry.  This {{w|Settlement of the Americas}} occurred around 14,500–11,000 BCE, as shown in the chart. However, a {{w|Settlement_of_the_Americas#Chronology|second theory}} suggest that an early wave of humans reached North America over 20,000 years ago 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 unhappy with the climate changes. And since the ice withdraws north when it gets hotter this glacier didn't have much of a choice. However this is a slow process and according to the chart the glacier first retreated over the Canadian border around 8400 BCE 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}}. Here it is {{w|Origin_of_the_domestic_dog#Time_of_domestication|mentioned}} that {{w|dogs}} separated from {{w|Gray wolf|wolfs}} about 23,500 years ago, but that there was an event around 15,000 years ago (13,00 BCE) which increased the population size and that may be attributable to domestication events. But if humans are responsible for the creation of the dog species it may have occurred several thousands of years before.
|-
|| [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}}. Like mammoths, 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 less than 1500 years 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 lasted over 4000 years, between 11,000 and 7000 BCE so 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 || The temperature almost reached 1.5°C below the 1961-1990 average before it got colder. 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}}. The information in this element is basically written towards the end of the section on this lake's  {{w|Lake_Agassiz#Geological_progression|geological progression}}, and the date given fits with the chart at 11,000 BCE and mentioning that it causes the Younger Dryas stadial.<br>The mentioning of the melting water causing a cooling in the northern hemisphere references a similar event that could also happen today. If the ice on {{w|Greenland}} melts too quickly it could mess with "the pump" that runs the {{w|Gulf Stream}} and cause a {{w|shutdown of thermohaline circulation}}, which would actually end up cooling {{w|Europe}}, especially the northern part and the {{w|British Islands}} (and everything east of {{w|Greenland}} in the {{w|North Atlantic}}), in spite of possibly still generally increasing temperatures on a global scale. This could be a major problem for farming in Europe!<br>The movie {{w|The Day After Tomorrow}} was based on this shutdown, although it then took it to an (impossible) extreme with super cyclones that cooled down the entire northern hemisphere into an ice age in a few days... In the Younger Dryas this effect caused the Earth to cool down less than one degree over 1000 years before the warm up began again.

|-
| 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}} is from 11,000 BCE as noted in the chart.<br>Finally the temperature has risen enough that there is space between the left border of the chart and the curve for writing facts also on that side of the curve. This took 9,000 years.

|-
| 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 decreasing temperatures the warm up of Earth resumes. Over 3000 years the temperature increases 2.5°C reaching a maximum and a long stable plateau around 7500 BCE. This temperature is 0.5°C above above the 1961-1990 average. But at the time of this comic that temperature had been surpasses just 26 years after the average period ended. It took 3000 years for 2.5°C, the last 100 years the temperature has increased 1.0°C...
|-
| 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 was the beginning of the ''Agricultural Revolution'', also 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}} located around the Nile in Egypt and curving into the part of {{w|Western Asia}} over the {{w|Arabian Peninsula}}.<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}} they were not related to tigers and generally most saber-toothed "cats" are not even related to 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 migrated across {{w|Beringia}} into Eurasia before they disappeared from North America.{{Citation needed}}

|-
| 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 || Unlike the Sea People (at 1200 BCE), Pokemon are not real. This faux-extinction is likely a reference to the recent {{w|Pokémon Go}} game, which Randall spoofed in [[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. According to the last part of the graph it may rise by as much in less than 200 years due to human cause global warming..
|-
| Rising seas cut off the {{w|land bridge}} between North America and Asia || 8700 BCE || 0.1 || The {{w|Beringia}} was also references when it was freed of ice in 15,000 BCE. This is an example of what happens when the temperature rises and glaciers melt. This could happen again now as the temperature rise causes ice on {{w|Greenland}} and {{w|Antarctica}} 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 out 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 recent 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 ||
|-
| Rise of the {{w|Indus Valley civilization}} || 3300 BCE || 0.5 ||
|-
| Invention of {{w|writing}} in {{w|Sumer}} “{{w|prehistory}}” ends, “{{w|history}}” begins || 3200 BCE || 0.5 || Writing was referenced at the top of the chart as one of the skills not yet developed back then. Any knowledge we have before this invention rely on what can be dug up and inferred from the findings. This is called prehistory. After this day it has been possible to find descriptions of people and events, and that 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]]. Interestingly enough there are only two facts in that previous comic, and the other fact in the main comic was regarding results of cancer research and funding for such research was referenced the week after this comic in [[1736: Manhattan Project]] (and nuclear weapons is also mentioned in this comic at 1950 CE). But it could be a coincidence.
|-
| 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 ||
|-
| {{w|Imhotep}} || 2600 BCE || 0.4 ||
|-
| {{w|Maya civilization|Mayan}} culture emerges || 2600 BCE || 0.4 ||
|-
| {{w|Great Pyramid}} constructed || 2650 BCE || 0.4 ||

|-
| rowspan="3"| 2500  <small>BCE</small>
| {{w|Corded Ware culture}} in Europe || 2500 BCE || 0.3 ||
|-
| [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> Stonehenge completed || 2200 || 0.3 || The drawing is a 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.
|-
| {{w|Chariots}} developed || 2000 BCE || 0.3 ||

|-
| rowspan="3"| 2000  <small>BCE</small>
| {{w|Alphabetic writing}} developed in Egypt || 1750 BCE || 0.2 || 
|-
| Last mammoths on a tiny Siberian island go extinct || 1650 BCE || 0.2 ||  Most of these animals died out in the {{w|Quaternary extinction event}} that took out also a lot of the {{w|Pleistocene megafauna}}, including the {{w|woolly rhino}} also mentioned in the chart. These two animals likely became extinct in part due to {{w|Holocene extinction|humans hunting them to extinction}} in a period where climate change had already stressed the animals. Indirectly humans may thus also have caused the extinction of the {{w|Saber-toothed cat}} also mentioned here. That humans may have caused these animals extinction even this early may be one reason that Randall has included them. Most of the mammoths died out before 8000 BCE but {{w|Woolly_mammoth#Extinction|some survived in remote areas}} and the last known population lived on {{w|Wrangel Island}} in the {{w|Arctic Ocean}} until 2000 BCE (so it seems Randall has given them 250 years more than what is noted on Wikipedia).
|-
| {{w|Minoan eruption}} || 1600 BCE || 0.2 ||

|-
| rowspan="5"| 1500  <small>BCE</small>
| {{w|Iron smelting}} || 1400 BCE || 0.1 ||
|-
| {{w|Olmec}} civilization develops in Central America || 1350 BCE || 0.1 ||
|-
| [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...
|-
| Invasion of the {{w|Sea peoples}}* <br>* A real thing || 1200 BCE || 0.1 || 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 foot note. 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 around this time.
|-
| {{w|Polynesians}} explore the Pacific Ocean || 1000 BCE || 0.1 ||

|-
| 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 || At this point the temperature has fallen half a degree back down to just a bit above the the 1961-1990 average. It will stay stable there for a long time from 1200 BCE and not until after 900 CE, after more than 2000 years, will there be any significant changes in temperature (at that time temperature falls even further). So one more long period with almost no temperature changes.
|-
| {{w|Solomon}} || 1000 BCE || 0.1 ||
|-
| {{w|Iliad}} and {{w|Odyssey}} composed || 900 BCE || 0.1 || In this way Randall makes it clear that the "history" of these two fairytales are written more than 300 years after and thus cannot very likely have anything to do with reality. For some reason Randall only mentions when religious figures like {{w|Buddha}}, {{w|Jesus}} and {{w|Muhammad}} (supposedly) lived but does not note when for instance the {{w|Bible}} or the {{w|Quran}} was written, which would have displayed a similarly much later time of writing than of the actual events mentioned taking place (and thus also indicating the fairytale type of stories they must be). Randall has specifically avoided using the more commonly used BC for before Christ, and instead uses CE for {{w|common era}} and BCE (before common era) in this chart. Thus avoiding the mentioning of religion in relation to the timing.
|-  
| Rise of {{w|Greek city-states}} || 800 BCE || 0.1 ||
|-
| {{w|Neo-Assyrian}} empire || 800 BCE || 0.1 ||
|-
| {{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  ||
|-
| {{w|Confucius}} || 550 BCE || 0.0 ||

|-
| 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}} (also known as 300 Spartans) but referenced by comparing the event with the 2007 movie ''300'' about this battle. But Randall notes that in the real world the fighting of course occurred at regular speed and that they probably had more clothing on in the real world than in the fictionalized action movie.
|-
| {{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 ||
|-
| {{w|Alexander the Great}} || 350 BCE || 0.0 ||
|-
| {{w|Mayan hieroglyphics}} || 250 BCE || 0.0 ||
|-
| {{w|Ashoka the Great}} || 250 BCE || 0.0 ||
|-
| {{w|Paper}} invented || 200 BCE || 0.0 ||
|-
| {{w|Asterix}} || 100 BCE || 0.0 || A reference to The Adventures of Asterix a comic series. The comic is set in 50 BCE to make it realistic for Asterix to interact with {{w|Julius Caesar}}  who correctly below has been listed around 50 BCE as he died in 44 BCE. Or course Caesar could be listed when he was politically active (from about 60 BCE) whereas Asterix around the time of his birth. Since Asterix is a fictional character his presence is in line with that of the inclusion of the timing of the Odyssey and of the last Pokémon.
|-
| {{w| Teotihuacan|Teotihuacán}} metropolis || 100 BCE || 0.0 ||
|-
| {{w|Julius Caesar}} || 50 BCE || 0.0 ||
|-

|-
| rowspan="8"|1  <small>BCE</small><br>1  <small>CE</small>
| [At the year 0, there is instead two numbers for each of the two scales before (1 BCE) and after Christ (1 CE)] || 1 CE || -0.1 || Originally the year range went directly from 1 BC to 1 AD. The year zero has since been added for use for instance in astronomical calculations. Maybe this is what is referenced here where the year 0 is not written but both 1 BCE and 1 CE.{{Citation needed}}
|-
| {{w|Roman Empire}} || 1 CE || -0.1 ||
|-
| {{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 ||
|-
| {{w|Gupta empire}} || 700 CE || -0.1 ||
|-
| Various groups take turns sacking {{w|Rome}} ||  550 CE || -0.1 ||
|-
| {{w|Attila the Hun}} || 550 CE || -0.1 ||

|-
| 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 ||
|-
| [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> Medieval warm period in Europe and some northern regions (too regional to affect the global average much) || 900 CE || 0.0 ||
|-
| {{w|Leif Eriksson}} || 950 CE || 0.0 ||

|-
| 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 ||
|-
| [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 ennough 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|Ghengis Khan}} || 1200 CE || -0.2 ||
|-
| {{w|Zheng He}}’s fleet explores Asia and Africa ||  1400 CE || -0.3 ||
|-
| {{w|Aztec Empire|Aztec Alliance}}  || 1400 CE || -0.3 ||
|-
| {{w|Printing press}} || 1450 CE || -0.3 ||
|-
| {{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  || For years after 1500 CE the CE is dropped and the years increase with only 100 instead of 500 although the scale stays the same. Inventions just happens so much faster in these last five hundred years up until today. So there are not really enough space to write all the important stuff and Randall has had to select very biased. So he included {{w|Isaac Newton}} but leaves out {{w|Albert Einstein}} and he includes {{w|airplanes}} but leaves out the {{w|car}} etc.
|-
| {{w|Shakespeare}} || 1600 CE || -0.3 ||4

|-
| rowspan="2"| 1600 
| {{w|Isaac Newton|Newton}} || 1650 CE || -0.4 ||
|-
| [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 below the 1961-1990 average, 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 where the temperature reached a minimum of 0.4°C below the 1961-1990 average, the coldest it had been in more than 11,000 years and the coldest it has been during any human civilization. It was a harsh time in Europe. In the winter it was so cold that the river {{w|Thames}} {{w|Little_Ice_Age#Europe|froze over}} hard enough for holding {{w|River Thames frost fairs}}. This could be done between 1607 and 1814. And in 1658 {{w|Sweden}} managed to cross both {{w|Little Belt}} and the {{w|Great Belt}} in the {{w|March Across the Belts}} to invade {{w|Copenhagen}} in {{w|Denmark}}. It was a highly risky operation as the strong currents usually would not leave these belts ice over completely. But it was successful and only possible due to the harsh winters of the Little Ice Age again proving how much half a degree in global warming can mean.

|-
| rowspan="2"| 1700
| {{w|Steam engines}} || 1750 CE || -0.4 ||
|-
| {{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  ||
|-
| {{w|Electrical telegraph|Telegraphs}} || 1830 CE || -0.3 ||
|-
| [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|Airplanes}} || 1900 CE || -0.3 ||
|-
| {{w|World Wars}} || 1930 CE || -0.2 ||
|-
| [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 ||
|-
| {{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 origins of the internet dates back to 1960 but it first became widely used in 1980 but it was the linking of commercial networks and enterprises in the early 1990s that marks the beginning of the transition to the modern Internet. By placing the invention of the {{w|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. Randall has before been after incidents where cause and effects like this has been used without any proof that it was not a coincidence. This is where the temperature again reached above the 1961-1990 average. This of course had to occur before 1990 as the 1960 temperature was below this average.

|-
| rowspan="2"| 2000
| {{w|Northwest Passage}} opens || 2000 CE || 0.4 || This was the first solid evidence that something had changed. When companies can see the possibility to sail different routes to save money because global warming has removed the sea ice in regions that has always been covered in ice during modern time, then it suddenly becomes clear to even more lay people that something is changing, disregarding 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. 

|-
| 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. This was what Randall already asked about what would be like in the +1 ice age unit (IAU) panel in [[1379: 4.5 Degrees]]. So he has already tried to yell to us about this two years ago, and he even started out back in [[164: Playing Devil's Advocate to Win]] almost 10 years ago. Seems he will get to ''enjoy quite a ride'' as he "wished" for back then. Also note that 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 already before 2200 CE if we could continue to increase global warming as we do now. As we might not survive (at least not like we do today) past 2100 if this trend keeps up, there might come a natural stop to releasing carbon dioxide and other greenhouse gasses into the atmosphere. But then again some of the positive feedback may already have taken over releasing large quantities of such gasses when the {{w|permafrost}} of the large northern {{w|tundra|tundra's}} melts... 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 et al. (2012) - [http://www.nature.com/nature/journal/v484/n7392/full/nature10915.html Nature], [http://www.atm.damtp.cam.ac.uk/mcintyre/shakun-co2-temp-lag-nat12.pdf (pdf)]
* Marcott et al. (2013) - [http://science.sciencemag.org/content/339/6124/1198 Science], [http://www.atm.damtp.cam.ac.uk/mcintyre/shakun-co2-temp-lag-nat12.pdf (pdf)]
* Annan and Hargreaves (2013) - [http://www.clim-past.net/9/367/2013/cp-9-367-2013.html Climate of the Past] [http://www.jamstec.go.jp/frsgc/research/d5/jdannan/LGM_temp.pdf (pdf)]
* {{w|HadCRUT#HadCRUT4 wikipedia|HadCRUT4}} - [http://www.metoffice.gov.uk/hadobs/hadcrut4/ Official site] 
* {{w|Intergovernmental_Panel_on_Climate_Change|IPCC}} -[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
:::[A guy with a white knit cap 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 out 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
::[Randall spelled Iliad wrongly this time:]
::Illiad 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
::[Randall spelled Attila wrong:]
::Atilla 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 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, and also some that are bigger than this one (for instance [[1110: Click and Drag]]). 
**But 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 "L"s.
**Attila the Hun becomes ''Atilla the Hun'' with ''one'' T and ''two'' L's.
**Pokémon is spelled ''Pokemon'', but then again that is not so strange for Randall (see [[1647: Diacritics]]). But he usually spells it correctly as in the recent comic [[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.
*Notably absent are the following facts
**1850: methodical temperature record begins. Although 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, which 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. And as is clear from the curve the temperature has been very stable these last 10,000 years which may explain why human civilization has peace from rapid changes in the environment to develop in the first place. And now it seems that we are causing this stable plateau to come to an end, and that was the point of the comic.
**The 300 million years prior to that, during which the earth was significantly warmer than now, underwent much more extreme temperature changes, and during which time it is presumed that life was present on the earth (but that cars were not).
*The comment for the previous entry also goes for this entry.

===Popularity of comic===
*This comic became so popular with a broader audience that 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 [http://www.explainxkcd.com/wiki/images/a/a6/1732_Earth_Temperature_Timeline_header_text_changed_for_all_comics.png all the comics] in the [http://www.explainxkcd.com/wiki/images/6/6d/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 [http://www.explainxkcd.com/wiki/images/6/62/1732_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 [http://www.explainxkcd.com/wiki/images/e/ee/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.

{{comic discussion}}

[[Category:Comics with color]]
[[Category:Large drawings]]
[[Category:Charts]]
[[Category:Timelines]]
[[Category:Line graphs]]
[[Category:Maps]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]] 
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Hairy]]
[[Category:Comics featuring real people]] <!--Pharao/Solomon/Cesar, Jesus? etc -->
[[Category:Multiple Cueballs]]
[[Category:Climate change]]
[[Category:Science]]
[[Category:Animals]]
[[Category:Music]] <!-- People with Guitars around Stone henge -->
[[Category:Fiction]] <!-- Iliad, Odyssey, 300 -->
[[Category:Sport]] <!-- Olympics -->
[[Category:Religion]] <!-- Jesus, Buddha, Muhammad  -->
[[Category:Internet]]
[[Category:Pokémon]]