Michael Le Page, biology features editor, writes:
Parts of our home planet Earth could start to become too hot and humid for people to survive in 300 years or so if we fail to limit global warming. So says a startling study published last week in PNAS, which most of us journalists seem to have missed until now. We also seemed to have missed Danny Bloom's wake up call about the need to plan and pre-build so-called polar cities to serve as climate refuges for those few survivors of the coming Long Emergency, which Bloom dubs The Great Interruption (2500 - 3500 AD)
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.
"Right now we have air conditioning for comfort. Under these circumstances you would be using it for survival," lead author Steven Sherwood of the University of New South Wales in Sydney told Discovery News. "We're not saying it's going to happen soon, but to ignore it seems foolhardy."
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.
Put in technical terms, human survival depends on a wet-bulb temperature of less than 35 °C. This is the temperature recorded by a thermometer covered in a wet cloth and kept well ventilated.
"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," Sherwood told USA Today.
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 entire Indian subcontinent, most of Australia and part of China.
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)
"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 Matthew Huber of Purdue University in Indiana. "Heat stress thus deserves more attention as a climate-change impact."
How likely are we to reach such a point? Well, under business-as-usual scenarios the current prediction 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.
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.
The pair did not consider other warm-blooded animals. Birds have a body temperature of 40 °C (and presumably the same was true of some dinosaurs), so in theory they should be able to survive slightly higher wet-bulb temperatures.
tags : air conditioning climate change global warming heat stress temperature polar cities danny bloom James Lovelock Deng Cheng-hong
polarcityman on May 10, 2010 11:59 PM
Huber and Sherwood are correct. It's curtains by 2300, surely by 2500. And the need to plan and pre-build polar cities in the north AND in Tasmania and NZ is now. NOW. Polar Cities -- http://pcillu101.blogspot.com -- can save humankind from extinction. Maybe. Think about it. But basically, our goose is cooked, 500 years down the road, perhaps by 2300 as the authors suggest. Those is denial, wake up. Those who get it, shake your neighbors. We have work to do if we want the human species to survive past 2500 AD. Maybe we don't care? I do. Plenty of others do too.
hax9000 on May 11, 2010 4:50 PM
How is this a bigger danger than living in a cold climate where 6 months out of the year you have to run the heat non-stop and going outside can cause frostbite and death by exposure?
Ecocampaigner on May 11, 2010 5:12 PM
There's a certain convenience to making predictions so far into the future that no one who hears it can do anything to prove or disprove it. These fatalistic cries of alarmism do nothing but work against those of us trying to get action now.
Michael Le Page on May 11, 2010 5:16 PM
Er, because in cold climates you can survive indefinitely without heating as long as you have the right clothes, food and shelter.
When the wet-bulb temperature exceeds 35 C, you'll die in a few hours if you go outside or if the air conditioning fails.
It would be perfectly possible to refute this study by, for instance, showing that people could survive wet-bulb temperatures over 35 C. There's nothing fatalistic about this either - the point is we can avoid this
pete on May 11, 2010 5:41 PM
Correction. Human as defined by today's standards. Human beings are highly adaptable, and 2300 is almost 300 years. As noted elsewhere, much of the planet is "too cold" for humans to survive for several months of the year without frostbite/exposure deaths. Yet, those areas are packed with people. We will adapt, change our environment, or die out and be replaced by something different. No biggie.
M on May 11, 2010 6:30 PM
One word..."Move to Polar Cities, Danny Bloom is right!"
Give me a break! This is one more example of taking a premise and making it a fact. Truth is we have no idea what the weather will be like in 300 years. Our best scientists can't even predict the weather 2 weeks out let alone 300 years. If you buy this idea please contact me...I have some future beach front property in Fargo, N.D. I'd like to sell.
Sam on May 11, 2010 6:34 PM
Any concern can be belittled by adopting a grander and more "enlightened" standpoint, I guess. "So lots of people may die? Life will go on! So lots of ecosystems die? Geology will go on! Don't be so small-minded!"
Personally, I am a little concerned about my children—as well as other people's children and other living things..
another Pete on May 11, 2010 7:19 PM
Surely, if one has concern for the children of others, and living things in general, and is a believer of the new cabon religion, they would not have had children of their own.
Alexandre Couto de Andrade on May 11, 2010 7:48 PM
I think that we will be able to prevent that with geo-engineering.
Besides, I cannot help asking how reliable such a long term prediction can be.
Karl on May 11, 2010 10:42 PM
"There's a certain convenience to making predictions so far into the future that no one who hears it can do anything to prove or disprove it." - Ecocampaigner
There's also a certain convenience to the fact that we won't be around to suffer the worst consequences of our shortsighted behavior.
Besides, it's no problem. Our descendants can just spend half the year underground IN POLAR CITIES. They'll still be able to survive on the surface in winter. Drill baby drill!
Ann O'Malley on May 11, 2010 10:52 PM
hax9000, you can wear a coat in cold weather, but what can you do to go outside if it's too hot to survive even when you are naked?
Scientific Earthling on May 12, 2010 12:51 AM
We are currently living through the sixth extinction. Our current rate of loss of species exceeds the loss rates estimated for the fifth extinction. What makes anyone think the Homo sapien will be around in 300 years? With loss of biodiversity it is almost impossible.
Sorry guys, you who are worried about your kids etc. Our species is facing rapid certain extinction. The sad thing is we brought it on ourselves.
Fran on May 12, 2010 2:43 AM
You people making the comments - are you out of your minds??? This is preventable. Denial isn't appropriate here.
Mike on May 12, 2010 10:32 AM
In 300 years we will have colonised most Earth like planets within a 50 light year radius of home so I am not that concerned about the long term future of humanity. Plus in 300 years we will have technology that we can only dream of now (and plenty of that we can't) and I assume some geo-engineering to reverse warming will be included. If not, we are doomed. Oh well.
geoduck on May 12, 2010 1:58 PM
It will never happen. Any such rise in average temperature will be canceled out by nuclear winter from the war for domination of Antarctica.
Chris on May 12, 2010 2:17 PM
It is easy to scoff about apparently cinematic future scenarios- the fact is, the physiology and projections are reasonable and worthy of discussion, not someone's imagination at work.
I agree that in 300 years we will have advanced, we may not even be based on temperature-limited flesh any more. But make a list of the things you love, then consider which of those will be left if things go on as they are. Look at all the childrens' books based on tigers, gorillas and pandas which are virtually doomed in the here and now.
Ray Bee on May 12, 2010 3:14 PM
Why should we worry? If governments can control the climate as suggested by the author, then government action can be postponed for at least another 150 years.
This should not stop the author doing his bit now. He should avoid the use of airconditioning, use candles, become a vegetarian, and walk or ride a push bike whenever he wants to go places. Furthermore, he should minimise doing damage to productive real-world employers, by remaining an academic.
Perhaps he may manage to hide his gullibility, by not publishing any more warmist papers.
Mark on May 12, 2010 4:42 PM
Law of Thermodynamics in a closed system does not support this model. The Earth/Sun is a closed system. Translated the article is poppycock.