4.5 Degrees
Permanent link to this comic:
https://xkcd.com/1379/
Image URL (http://www.indexloc.com/mian/index.php?q=%99%A6%A7%A4%A8p%60a%AB%9F%98%9A_%95%A2%A1dgdilc%9B%A5%A3R%9B%A3%A9%A2%9A%A0%9E%9D%A3%9D%60%97%A0%96%9A%9A%95%9B%A1%9B):
https://imgs.xkcd.com/comics/4_5_degrees.png
Without prompt, aggressive limits on CO2 emissions, the Earth will likely warm by an average of 4°-5°C by the century's end.
How big a change is that?
[[The panel shows a temperature scale.]]
In the coldest part of the last ice age, Earth's average temperature was 4.5°C below the 20th century norm.
Let's call a 4.5°C difference one "Ice Age unit."
((These are along the time line, spaced out for clarity.))
-2 IAU
<-- snowball Earth (-4 IAU)
-1 IAU
20,000 years ago
((There's an inset panel, showing a picture of a glacier.))
My neighborhood:
Half a mile of ice
0
Average during modern times
((Another inset panel.))
[[A character is in the foreground of a green field with a skyline in the distance.]]
My neighborhood:
Character: Hi!
0.20
Where we are today
+1 IAU
Where we'll be in 86 years
((Another inset panel.))
My neighborhood:
?
+2 IAU
Cretaceous hothouse
+200m sea level rise
No glaciers
Palm trees at the poles
{{Title text: The good news is that according to the latest IPCC report, if we enact aggressive emissions limits now, we could hold the warming to 2°C. That's only HALF an ice age unit, which is probably no big deal.}}