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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

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    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 9 '16 at 1:12
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    @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 9 '16 at 9:00
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    one wonders why the Northern Territories of Australia would remain habitable while Tasmania becomes uninhabitable! ;o) – Dikran Marsupial Sep 9 '16 at 10:23
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    According to this graph 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 9 '16 at 15:42
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    Any map this simplistic must be wrong--there's no regard for elevation. – Loren Pechtel Sep 10 '16 at 3:14
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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.

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    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 9 '16 at 11:30
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    @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. – Dikran Marsupial Sep 9 '16 at 11:35
  • Thanks for your answer, could you elaborate on the "motivated reasoning" about banks and how it relates to climate change? – user35657 Sep 10 '16 at 15:42
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    @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. – Dikran Marsupial Sep 10 '16 at 16:01
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    @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
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More of Vivienne Westwood's speech comes from Huffington Post http://www.huffingtonpost.co.uk/vivienne-westwood/vivienne-westwood-plan-to-stop-climate-change_b_8917340.html where she said "intellectuals" needed to "destroy the credibility of the press". In more detail she said

Most people now think climate change is under control, our leaders are taking care of it.

The press went on to tell us that the [Paris] agreement is not binding and the UN says we (business as usual) are on course to hit between +2.7 and +3.5. But most people ignore that unsettling part of the information. They already “got the story”. Once they got the story there is no room for other information, especially if it conflicts; the hole has been filled and everybody’s back to square one. People don’t see any other way than business as usual. No change.

then from the Climate Revolution page you link to expalins why the map does not stop there

Global warming is at the tipping point. If we go past it, we can’t stop it. All the methane kicks in.

This map is the world at 5 degrees. If you draw a line parallel with Paris, everything below that is uninhabitable. This means by the end of this century there will only be one billion people left. Our politicians, they are preparing for this.

These are extreme views. There is no scientific consensus for runaway climate change or that climate change will cause the human population to fall to 1 billion by 2100 (the United Nations recently projected 11 billion http://www.un.org/en/development/desa/news/population/2015-report.html).

Nor is the map particularly credible - the range of temperatures between currently habitable zones within that red area is already much wider than 5 degrees (think of the Tibetan plateau for example). And despite the crude line through Paris (the east coasts of North America and Asia are generally cooler than the west coasts of Europe and North America at the same latitude, for reasons associated with wind and the Earth's rotation), something more complicated has been drawn in the southern hemisphere, with an incredible treatment of northern Australia (currently largely hot desert)

Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

  • I've removed a comment stream, Please remember the Be Nice policy, including assuming good intentions. – Oddthinking Sep 10 '16 at 0:22
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    Please provide references for the following claims: That Westwood's views are extreme, and there is no scientific consensus. (The UN population report seems to be extrapolating fertility figures, and not factor in climate at all, which suggests it isn't a suitable model to make your point - unless they considered and entirely discounted it in the report - in that case, quote them saying that. – Oddthinking Sep 10 '16 at 0:28
  • The last paragraph seems to be an argument from incredulity. I couldn't see how it shows that the claim is wrong. – Oddthinking Sep 10 '16 at 0:32
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    @Oddthinking: The question when answered was about the map, but it has subsequently been changed. If you and others keep deleting comments, including references, there is little point in having a conversation – Henry Sep 10 '16 at 7:38
  • @Henry Sorry, many people have been editing the question to best fit criteria. Thanks for your answer! – user35657 Sep 10 '16 at 17:07
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Sherwood and Huber (2010) look at uninhabitability due to heat stress. They estimate that if the earth warms by 11-12 degrees Celsius, regions where more than 50% of the world's current population lives would become exposed to unprecedented heat stress: you couldn't live there without air conditioning, you couldn't work outdoors, you couldn't maintain livestock outside, and a power failure would put you at risk of death due to heatstroke.

But that's considerably more than 5 degrees of warming.

Abstract:

Despite the uncertainty in future climate-change impacts, it is often assumed that humans would be able to adapt to any possible warming. Here we argue that heat stress imposes a robust upper limit to such adaptation. Peak heat stress, quantified by the wet-bulb temperature TW, is surprisingly similar across diverse climates today. TW never exceeds 31 °C. Any exceedence of 35 °C for extended periods should induce hyperthermia in humans and other mammals, as dissipation of metabolic heat becomes impossible. While this never happens now, it would begin to occur with global-mean warming of about 7 °C, calling the habitability of some regions into question. With 11–12 °C warming, such regions would spread to encompass the majority of the human population as currently distributed. Eventual warmings of 12 °C are possible from fossil fuel burning. One implication is that recent estimates of the costs of unmitigated climate change are too low unless the range of possible warming can somehow be narrowed. Heat stress also may help explain trends in the mammalian fossil record.

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