<h1 id="article-title-1">From "New Scientist" website, regarding the article published in 2010 in the Proceedings of the National Academy of Sciences, which is directly referenced at the bottom:</h1>
<h1><a href="http://www.newscientist.com/blogs/shortsharpscience/2010/05/earth-2300-too-hot-for-humans.html#more">http://www.newscientist.com/blogs/shortsharpscience/2010/05/earth-2300-too-hot-for-humans.html#more</a></h1>
<h1>Earth, 2300: Too hot for humans</h1>
<div>15:26 11 May 2010</div>
<div> </div>
<div><a href="http://www.pnas.org/content/early/2010/04/26/0913352107"><i>Michael Le Page, biology features editor</i></a></div>
<h1>
<p>Parts of the planet could start to become too hot and humid for people to survive in a century or so if we fail to limit global warming. So says a startling study <a href="http://dx.doi.org/10.1073/pnas.0913352107">published last week in <i>PNAS</i></a><a href="http://www.pnas.org/content/early/2010/04/26/0913352107">, which most of us journalists seem to have missed </a><a href="http://www.google.com/hostednews/afp/article/ALeqM5jTXA_CTHXzXzc-HxwAVLW-nh-eww">until now</a><a href="http://www.pnas.org/content/early/2010/04/26/0913352107">.</a></p>
<p>Some regions would start to become too hot and humid for human habitation with a global temperature rise of 7 °C, the paper says. With a rise of 11 °C or more, most of the human population as currently distributed would either have to move or rely on air conditioning to avoid dying of heat stress.</p>
<p>"Right now we have air conditioning for comfort. Under these circumstances you would be using it for survival," lead author <a href="http://www.ccrc.unsw.edu.au/staff/profiles/sherwood/">Steven Sherwood</a><a href="http://www.pnas.org/content/early/2010/04/26/0913352107"> of the University of New South Wales in Sydney </a><a href="http://news.discovery.com/human/warming-human-temperature.html">told <i>Discovery News</i></a><a href="http://www.pnas.org/content/early/2010/04/26/0913352107">. "We're not saying it's going to happen soon, but to ignore it seems foolhardy."</a></p>
<span id="more"></span>
<p>The problem is that we cannot survive if our skin temperature exceeds 35 °C for more than a few hours. Although many people live and even work in temperatures of 45 °C or more, sweating keeps their skin cool as long as it's not too humid.</p>
<p>Put in technical terms, human survival depends on a <a href="http://en.wikipedia.org/wiki/Wet-bulb_temperature">wet-bulb temperature</a><a href="http://www.pnas.org/content/early/2010/04/26/0913352107"> of less than 35 °C. This is the temperature recorded by a thermometer covered in a wet cloth and kept well ventilated.</a></p>
<p>"The wet-bulb limit is basically the point at which one would overheat even if they were naked in the shade, soaking wet and standing in front of a large fan," <a href="http://content.usatoday.com/communities/sciencefair/post/2010/05/report-climate-change-could-render-much-of-world-uninhabitable/1">Sherwood told <i>USA Today</i></a><a href="http://www.pnas.org/content/early/2010/04/26/0913352107">.</a></p>
<p>At the moment, virtually nowhere on Earth has a wet-bulb temperature of more than 30 °C. But with a global rise of 11 °C, huge areas would have wet-bulb temperatures of more than 35 °C for part of the year. According to the climate model used by the team, these regions would include much of the eastern US, the <a href="http://earlywarn.blogspot.com/2010/05/heat-stress-in-india.html">entire Indian subcontinent</a><a href="http://www.pnas.org/content/early/2010/04/26/0913352107">, most of Australia and part of China.</a></p>
<p><img style="MARGIN: 0pt 20px 20px 0pt; FLOAT: left" class="mt-image-left" alt="Picture-6.jpg" src="http://www.newscientist.com/blogs/shortsharpscience/Picture-6.jpg" width="600" height="329"><i>Projected regional wet-bulb temperatures for an average global temperature increase of 12 C. Humans cannot survive wet-bulb temperatures over 35 C (Image: Steven C. Sherwood/Matthew Huberb)</i><br>
</p>
<p>"If warmings of 10 °C were really to occur in [the] next three centuries, the area of land likely rendered uninhabitable by heat stress would dwarf that affected by rising sea level," write Sherwood and co-author <a href="http://web.ics.purdue.edu/~huberm/CDPL.html">Matthew Huber</a><a href="http://www.pnas.org/content/early/2010/04/26/0913352107"> of Purdue University in Indiana. "Heat stress thus deserves more attention as a climate-change impact."</a></p>
<p>How likely are we to reach such a point? Well, under business-as-usual scenarios <a href="http://www.copenhagendiagnosis.com/">the current prediction</a><a href="http://www.pnas.org/content/early/2010/04/26/0913352107"> is for a 4 °C to 7 °C increase by 2100. In other words, in the worst-case scenario if we carry on as we are, some of our children might just live to see small parts of the world start to become too hot for human habitation.</a></p>
<p>In fact, the same limits would apply to all mammals, including livestock. If that is true, mammals would have died out in large parts of the world during past warm periods like the Palaeocene-Eocene Thermal Maximum 55 million years ago. This may well have happened, say Sherwood and Huber - fossil records of tropical regions are too poor to tell one way or the other.</p>
<p>The pair did not consider other warm-blooded animals. <a href="http://www.newscientist.com/article/mg20126942.000-whats-the-point-of-being-warmblooded.html">Birds have a body temperature of 40 °C</a><a href="http://www.pnas.org/content/early/2010/04/26/0913352107"> (and presumably the same was true of some dinosaurs), so in theory they should be able to survive slightly higher wet-bulb </a></p>
<p>-----------------------------</p>
<p><a href="http://www.pnas.org/content/early/2010/04/26/0913352107">http://www.pnas.org/content/early/2010/04/26/0913352107</a></p></h1>
<h1>An adaptability limit to climate change due to heat stress</h1>
<div class="contributors">
<ol id="contrib-group-1" class="contributor-list">
<li id="contrib-1" class="contributor"><span class="name"><a class="name-search" href="http://www.pnas.org/search?author1=Steven+C.+Sherwood&sortspec=date&submit=Submit">Steven C. Sherwood</a></span><a id="xref-aff-1-1" class="xref-aff" href="http://www.pnas.org/content/early/2010/04/26/0913352107#aff-1"><sup>a</sup></a><span class="xref-sep">,</span><a id="xref-corresp-1-1" class="xref-corresp" href="http://www.pnas.org/content/early/2010/04/26/0913352107#corresp-1"><sup>1</sup></a> and </li>
<li id="contrib-2" class="last"><span class="name"><a class="name-search" href="http://www.pnas.org/search?author1=Matthew+Huber&sortspec=date&submit=Submit">Matthew Huber</a></span><a id="xref-aff-2-1" class="xref-aff" href="http://www.pnas.org/content/early/2010/04/26/0913352107#aff-2"><sup>b</sup></a></li>
</ol>
<p class="affiliation-list-reveal"><a class="view-more" href="http://www.pnas.org/content/early/2010/04/26/0913352107#">+</a> Author Affiliations</p>
<ol class="affiliation-list hideaffil">
<li class="aff"><a id="aff-1" name="aff-1"></a>
<address><sup>a</sup>Climate Change Research Centre, University of New South Wales, Sydney, New South Wales 2052, Australia; and </address></li>
<li class="aff"><a id="aff-2" name="aff-2"></a>
<address><sup>b</sup>Purdue Climate Change Research Center, Purdue University, West Lafayette, IN 47907 </address></li></ol>
<ol class="fn-track">
<li id="fn-1" class="fn-edited-by">
<p id="p-1">Edited by Kerry A. Emanuel, Massachusetts Institute of Technology, Cambridge, MA, and approved March 24, 2010 (received for review November 19, 2009) </p></li></ol></div>
<div id="abstract-1" class="section abstract">
<h2>Abstract</h2>
<p id="p-3">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 <em>T</em><sub><em>W</em></sub>, is surprisingly similar across diverse climates today. <em>T</em><sub><em>W</em></sub> 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. </p>
<p>------------------------------------------</p>
<p>Vision2020 Post: Ted Moffett</p></div>