Randall Munroe does it again

A while back, XKCD shared this excellent comic about climate change, proposing the “Ice Age Unit”, or IAU, defined as 4.5 degrees Celsius, and justified as follows:

Image is headed by the 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.”

This is a pretty good way to think about global climate change, and it’s not actually too far off from how the scientists studying it in the 1890s and early 1900s looked at it as they tried to work out what was up with this whole “ice age” thing that seemed to be in our past. Now, Munroe has given us a much more in-depth look at Earth’s climate, going back to 20,000 BCE, and giving us a pretty good perspective on the current and imminent changes to our global average temperature:

This is a very, very long graph with time on the Y axis and temperature on the X axis. The X axis goes from -5 degrees C to +5 degrees C. The Y axis goes from 22,000 years ago at the top, to the year 2200 at the bottom. At the beginning, Earth is in an ice age, with a mile of ice over Boston. There is a small illustration of how that sheet of ice would have towered more than five times the height of the tallest buildings in the city. The temperature line then continues downward - forwards in time - through the slow warming out of the ice age, into the dawn of civilization. It goes past early farming, cave paintings, and metalworking, the rise and fall of ancient empires, the extinction of species like the saber-toothed cat, and a selection of the many occurrences on our planet in the last 20,000 years. It passes the first known opening of the Northwest Passage due to melting sea ice around 2009. When it reaches the 20th century, there is a sharp increase in temperature, and into the 20th century the line splits off into three possibilities - the best-case scenario of almost no more warming with incredible levels of action starting immediately, the optimistic scenario with two degrees C rise in temperature by 2100, and the path we are currently on, with the increase in temperature passing 4 degrees Celsius above the 20th century average by the year 2100.

“[After setting your car on fire] Listen, your car’s temperature has changed before.”


  1. Seth says

    A powerful graph. Quibble: It’s a near-certainty now that habitation of the Americas occurred in multiple waves via land and sea, instead of one singular migration, and very likely included Polynesians colonising South America independently of the land-bridge-and-aleutan-hopping peoples from Siberia. The weight of evidence should be enough to shift consensus on these topics in the next few years, but given the weight of that consensus to date, it is forgivable that such detail isn’t reflected in this sort of compilation.

  2. StevoR says

    Excellent, fascinating graphic which is most informative – and puts things powerfully into perspective. Thanks.

  3. StevoR says

    A bit off topic,, sorry, but this is historic news somewhat related here too :


    A project led by adventurer David Hempleman-Adams that aimed to sail the Arctic’s North East and North West passages in a single season has completed its quest. ..(snip) … Franklin’s other ship, HMS Erebus, was found two years ago. The explorer’s attempt to chart the NWP in the 1840s was undone by thick ice, and cost the lives of more than 120 men.

    Good news or bad – both at the same time but with very worrying implications.

  4. StevoR says

    Off topic but an article of possible interest here for ya :


    Yacht sails through low-ice Arctic sea routes By Jonathan Amos
    BBC Science Correspondent 13 September 2016

    A project led by adventurer David Hempleman-Adams that aimed to sail the Arctic’s North East and North West passages in a single season has completed its quest. The yacht Northabout left Bristol, UK, in June and circled the North Pole in an anticlockwise direction. Its exit from Canada’s Lancaster Sound on Monday signalled the successful navigation of both sea routes. .. (snip) .. Ice has been so minimal around the islands that make up Canada’s northern polar region that Northabout was able to sweep through the NWP in just two weeks.

    This strikes me as something which hasn’t been given enough notice – this year’s second lowest Arctic sea ice minimum and its consequences are really quite, well, bloody terrible especially considering what’s in the pipeline as greenhouse gases continue to accumulate and will have a millennia plus (?) lingering impact on our pale blue dot in The Black.

    PS. Hope you are okay, Abe Drayton, and are still going to blog here, ideally more frequently, please?

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