When denier ideologues make the transition to accepting the reality of anthropogenic global warming, one of the arguments they start to use tends to go something along the following lines: “Sure, the polar bears might get screwed over, but otherwise things will be just great. Crop yields will increase and northerners will get to have their own sun-drenched beaches”. You wish. New research* indicates that beyond temperature rises of 7C, “zones of uninhabitability” will begin to overspread much of the world (“An adaptability limit to climate change due to heat stress” by Sherwood & Huber 2010). Not a Mediterranean world, more like Mad Max in Waterworld.
Of late climate models have been leaning to the upper range of the IPCC’s projections for global warming, e.g. the median forecast from a recent MIT study gives a rise of 5C by 2100 (with a 10% chance it will exceed 7C). According to the Sherwood paper, “peak heat stress” (quantified by the wet-bulb temperature) never climbs above 31C across today’s climes, which is safely below the body’s normal temperature of 37C. But with a global temperature rise of 7C possible by as early as the late 21st century – even without accounting for predictable tripwires such as accelerated release of Siberian and Arctic methane – some regions of the world will be subjected to peak wet-bulb temperatures of 35C, inducing “hyperthermia in humans and other mammals, as dissipation of metabolic heat becomes impossible“. With a global temperature rise of 11-12C, a belt of uninhabitability will come to encompass the bulk of today’s densely populated areas.