A new set of model results from Purdue University give us a foreshadowing of what the effects of global warming-induced climate disruption will be on the nation that currently puts the most greenhouse gases into the air: the United States.

In an article to be published later this week in the Proceedings of the National Academy of Sciences, geophysicist Noah Diffenbaugh and colleagues Jeremy S. Pal, Robert J. Trapp and Filippo Giorgi discuss the results of a five-month supercomputer simulation of global warming across North America over this century. This simulation exercise ranks as one of the most sophisticated ever run; the model was able to consider effects on individual regions 25 kilometers square, down from 50 square kilometers used in previous models.

It's something of an article of faith among the remaining holdouts denying the existence of global warming that computerized climate models, as they abstract aspects of the climate, are essentially useless -- and (implicitly) if they had more details, they'd show that all was right with the world. Unfortunately, as our modeling methods and technologies have gotten better, quite the opposite has occurred. These days, reports from computer models are apt to show that things are worse than we thought, climate-wise. This one is no exception:

Some of these expectations include:

The desert Southwest will experience more heat waves of greater intensity, combined with less summer precipitation. Water is already at a premium in the four-corners states and southern Nevada and, as years pass, even less water will be available for the region's burgeoning populations, with extreme hot events increasing in frequency by as much as 500 percent.

The Gulf Coast will be hotter and will receive its precipitation in greater volumes over shorter time periods. "The region actually will get more rainfall than it does now, but it will not be steady," Diffenbaugh said. "We project more dry spells punctuated by heavier rainfalls. We need to perform further analyses to understand how much of this is related to tropical cyclone activity."

In the northeastern United States - roughly the region east of Illinois and north of Kentucky - summers will be longer and hotter. "Imagine the weather during the hottest two weeks of the year," Diffenbaugh said. "The area could experience temperatures in that range lasting for periods of up to two months by century's end."

Similarly, the continental United States will experience an overall warming trend: Temperatures now experienced during the coldest two weeks of the year will be a past memory, and winter's length will diminish as well, according to the model.

The model, Diffenbaugh said, assumes that greenhouse gases will attain a concentration more than twice their current levels.

And it's that line that gives us a sliver of hope. The current atmospheric CO2 concentration is around 380ppm, so twice that is 760ppm; serious efforts to move off of a carbon-intensive global economy should allow us to keep CO2 concentration around 450-500ppm -- still higher than is safe, but potentially not disastrous. In many respects, the 760+ppm Diffenbaugh used for this simulation represents a scenario in which efforts to shift us off of carbon-intensive technologies fail. This isn't a worse-case scenario; that would be one in which we start getting dramatic greenhouse feedback effects, such as an unconstrained release of methane into the atmosphere, making the heat capture even worse.

Diffenbaugh suggests that it would take a substantially faster supercomputer to improve the results: "... we'll need a computer at least 100 times as powerful as the cluster we used to really improve the accuracy." Such a computer should be available within ten years, if current trends hold true.

It would be interesting to see how well such simulations predict the past: ie the trend for the nineties and noughties based on data collected up to the eighties.

Otherwise the naysayers will dismiss this as just another alarmist prediction, and keep their heads in the sand.

Posted by: Tony Fisk on October 17, 2005 5:53 PM

Exactly! This would seem to be the methodical nail-in-the-coffin. Hasn't anyone done this?

Posted by: Bill Huber on October 17, 2005 7:54 PM

The article at the first link discusses this -- they do:

"We checked our model's performance by analyzing the period from 1961 to 1985 for which, of course, we do not need a prediction," Diffenbaugh said. "The model performed admirably, which tells us we've got a good understanding of how to represent the physical world in terms of computer code."

Posted by: Jamais Cascio on October 17, 2005 8:08 PM

Wow.

It looks like Mexico is going to get royally fucked.

Can you say "millions of environmental refugees?"

Sure, I knew you could.

Posted by: Stefan Jones on October 17, 2005 9:17 PM

"Rillions of environmental mefugees"

Curses!

Posted by: Tom Edwards on October 18, 2005 9:23 AM

"This isn't a worse-case scenario; that would be one in which we start getting dramatic greenhouse feedback effects, such as an unconstrained release of methane into the atmosphere, making the heat capture even worse."

Aren't we now seeing these positive feedbacks? Melting Siberian tundra releasing massive amounts of methane, which is a many times more effective greenhouse gas than CO2... Arctic ice diminishing at an accelerating rate, reducing reflectance, increasing heat absorbtion...Reduced plant growth in higher temps as Europeans have observed, therefore reducing natural carbon sequestration.

Seems to me as dire as this looks, it actually understates the case, if it doesn't incorporate these and other positive feedback loops. We've been heading in this direction for more than a century, of course, but G(lobal) W(arming) Bush sure isn't helping us head it off...

Posted by: Dan Combs on October 19, 2005 8:15 AM

In the northeastern United States - roughly the region east of Illinois and north of Kentucky - summers will be longer and hotter. "Imagine the weather during the hottest two weeks of the year," Diffenbaugh said. "The area could experience temperatures in that range lasting for periods of up to two months by century's end."

Actually, New England experienced something like this the past summer, with a continuous period of high-temp days lasting well over a month. It certainly gave us a "good" taste of G.W. to come!

Posted by: w_m_bear on October 19, 2005 6:07 PM