19

I've seen this image circulated on message boards a few times, and I'm wondering if it has any scientific basis.

Red is uninhabitable land, and green is all that is left after a global rise of 5°C.

enter image description here

source

  • 1
    It might be Fahrenheit, which would be about 2.5 Celsius. –  Sep 09 '16 at 00:46
  • 7
    The main issue here is to define "uninhabitable." Based on a literal reading this is almost obviously false since humans already inhabit areas whose average global temperatures differ by more than 5 degrees, e.g., Bangkok vs Boston. Also, does this say that all of the arctic and Siberia become habitable? What about Antarctica? – Patrick87 Sep 09 '16 at 01:12
  • 9
    @Patrick87 Climate change isn't only about the temperature change itself, though, it's about the knock-on effects of that temperature change on weather patterns, frequency of extreme weather events, crop viability, desertification, spread of diseases, etc etc. No idea if the map is accurate (I suspect it's exaggerated) but a 5 degree temperature increase across every inch of the planet would have huge consequences beyond simply being a bit hotter everywhere. – user56reinstatemonica8 Sep 09 '16 at 09:00
  • 6
    one wonders why the Northern Territories of Australia would remain habitable while Tasmania becomes uninhabitable! ;o) –  Sep 09 '16 at 10:23
  • 1
    @fredsbend the claim comes from Europe so I doubt that... – Sklivvz Sep 09 '16 at 11:46
  • 3
    According to this graph https://en.wikipedia.org/wiki/Geologic_temperature_record#Overall_view the global temperature during the Eocene was 15 to 25 degrees F warmer than at present. And it seems the earth was not uninhabitable then. – GEdgar Sep 09 '16 at 15:42
  • 2
    That was before the evolution of Hominidae though, so it doesn't mean the Eocene would have been inhabitable by modern humans. It is a valid point against the hyperbolic claims of destroying all life etc. –  Sep 09 '16 at 17:13
  • 1
    @ OP: I'm pretty sure if you flag this question for moderator attention, you can get it merged with your regular account (if desired). @Sklivvz Am I correct on that? – Reinstate Monica -- notmaynard Sep 09 '16 at 18:09
  • 1
    @iamnotmaynard he can self merge the two accounts via the /contact page – Sklivvz Sep 09 '16 at 18:16
  • 5
    Any map this simplistic must be wrong--there's no regard for elevation. – Loren Pechtel Sep 10 '16 at 03:14
  • 2
    Keep in mind that if GLOBAL temperatures go up by five degrees, that doesn't mean that areas in red will be five degrees warmer. Some areas in red might be underwater, or will have their groundwater contaminated by seawater. If another area gets all its water from winter ice melt-off and there's no more winter ice, it might become unlivable. If ocean currents shut down, then some areas will go up by much, much more than 5 degrees C. It's not just a matter of whether five degrees warmer makes a place too hot to live, it's what that five degrees, on a global basis, means in a variety of ways. – PoloHoleSet Sep 13 '16 at 18:19
  • 1
    That's not to mean that I claim these claims are credible, I haven't assessed them, but talking about the ripple effects of a global increase in temperatures goes beyond just the localized temperatures, so keep that in mind. – PoloHoleSet Sep 13 '16 at 18:23

3 Answers3

17

Screenshot of map showing impacts of a 4C temperature increase

No. Here is an interactive map from the UK Met Office showing the likely impacts of a 4C rise. For instance if you click on the button over Argentina it suggests a 40% reduction in maize and wheat yields at low latitudes. I think it is rather unlikely that a further degree would go from reduced crop yields to uninhabitability. As usual the IPCC WG1 and WG2 reports are a better source of information. Update, in the talk, Westwood says that the map is actually for 4 degrees, so the MetOffice impacts map directly constradicts Westwood's chart.

BTW the final draft of the IPCC AR5 WG2 report seems to use the word "uninhabitable" twice, and on neither occasion does it refer to large areas of the planet, but more local problems (extreme weather/sea level rise), so I don't think there is any support for Westwood's chart from the relevant IPCC report either.

The comment about climate change being unstoppable after it goes past 2C and will inevitably then reach 4C has no basis in science AFAICS. In the absence of "tipping points" (e.g. sudden release of GHGs from methane calthrates) the rise in temperature is expected to be a fairly smooth function of cumulative fossil fuel (and land use change) emissions, there is no special breakpoint at 2C as far as I am aware.

A question about her (rather extreme) views on banking is probably in order as well, as it suggests there may be some "motivated reasoning" behind her take on climate change.

  • 7
    The 2 degrees limit does have a basis in evidence, I don't know all the details but it was agreed as the best estimate for the level below which the "most serious effects" could be avoided, by the 2005 "Avoiding Dangerous Climate Change" scientific symposium, amongst others. Like every estimate, there's disagreement about the details, in particular factors like increases in arctic methane evaporation which could cause feedback loops, but I believe there's a consensus that it's a reasonable estimate. – user56reinstatemonica8 Sep 09 '16 at 11:30
  • 3
    @user568458 The 2 degrees limit is an estimate based on our ability to deal with the likely impacts, but it isn't a tipping point that makes further warming to 4C inevitable. It is possible that Westwood has misunderstood the purpose of the 2C limit and conflated it with the concept of there being warming in "the pipeline" (i.e. warming that will happen because of our historical carbon emissions that will take place one the thermal inertia of the oceans etc has played out). We could limit our emissions now such that we reach 2C and stabilise there without further warming. –  Sep 09 '16 at 11:35
  • Thanks for your answer, could you elaborate on the "motivated reasoning" about banks and how it relates to climate change? –  Sep 10 '16 at 15:42
  • 1
    @SamC I just mean that it is possible that her concern is really about social/economic justice rather than climate change and was being insufficiently self-skeptical in the assessment of information on climate change (in order to maximise its value in arguing for the social/economic justice issues). Sadly human beings are rather susceptible to that sort of bias, which often ends up being counterproductive however well intensioned. –  Sep 10 '16 at 16:01
  • @DikranMarsupial Thanks, a valid thought to consider! –  Sep 10 '16 at 17:06
  • The rise in temperature is a fairly smooth function of cumulative fossil fuel*, citation needed. There may well be tipping points and chaotic behaviour. Not saying that there are, but a statement that there aren't needs to be backed up by evidence. The truth is that we're currently not sure.
    • – gerrit Sep 13 '16 at 18:18
  • @gerrit basic physics suggests that this is the case, tipping points generally require a substantial new feedback somewhere (e.g. calthrates), but I don't think there is any evidence that there is a tipping point at 2C. I'll have a think about a better wording. –  Sep 14 '16 at 11:03
  • 1
    @DikranMarsupial I agree that there is no evidence for a tipping point at 2°C. That would be a more careful formulation than to claim that there is not. – gerrit Sep 14 '16 at 11:24
  • @Mindwin still works for me. –  Dec 13 '16 at 14:45
  • @DikranMarsupial good to know! – Mindwin Remember Monica Dec 13 '16 at 15:16