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Retrospections Climate Change by Degrees
Climate Change by Degrees
Based on a Hot Zone blog entry
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Posted:   08/01/10
Author:    Alison Hawkes

Summary: There are many ambiguities in forecasting climate change. New reports are attempting to get to the 'nuts and bolts' of the problem, allowing people to clearly see the consequences of each degree of warming. Such information is important in understanding the future of life on Earth.

What a degree means

Image from NASA
Climate change scenarios are usually summed up in terms of expected change by a certain year. Like sea levels will rise by x amount by 2020 and y amount by 2050. Or by parts per million of CO2 in the atmosphere.

But because no one really knows what kind of carbon dioxide increases we’re facing (that having to do with the CO2 cutting regimen we choose), the whole forecasting effort becomes very ambiguous. That’s led some to throw their hands up on achieving greenhouse gas reductions in favor of adaptation planning.

A new report issued by the U.S. National Research Council takes a different approach. It orients climate change scenarios to degree increase in temperature to show what each degree gets you in impact.

“An important reason for using warming as a reference is that scientific research suggests that many key impacts can be quantified for given temperature increases,” the report states.

It’s a very nuts and bolts approach, allowing for people to see clearly the consequences of each degree of warming and determine what is the acceptable level of risk. For members of Congress debating a climate change bill, the report provides a handy reference point for making decisions that will impact the Earth for centuries or longer.

Let’s look at food production. Depending on the species and other factors like rainfall, many crops respond well to a 1-2 degree C temperature increase. Anything higher and things start to look dicey.

Wildfire in Santa Clarita, California in October 2007.
Asian rice fairs comparatively well, but U.S. and African maize, Indians wheat, and U.S. soybean crops show a sharp drop-off in yield. U.S. maize will see a stunning 11 percent drop in yield per degree C of warming. That doesn’t sound good. Not only does that feed Americans, but about 40 percent is currently exported to fill bellies in the rest of the world.

One degree C warming also increases wildfires in the western U.S. by 200-400 percent, depending on location and available fuel. It was also reduce rainfall in the American Southwest, Mediterranean, and southern Africa by 5 -10 percent.

Under a 2 degree C temperature increase, the southwest and central part of the U.S. would see three times the number of high heat days, exceeding 38 degree C or 100 degree F. You get the picture.

Climate change skeptics often minimize the impact of a couple degrees increase. Who doesn’t like warmer weather? But put in concrete terms, we may one day miss the comfort of a cold winter day by the fire. Or in California, a bleak, foggy day spent in a cafe.

Warm as the Arctic

Far North off the coast of Greenland is Ellesmere Island, a mountainous, icy patch of earth that supports only one species of woody plant, the tiny, slow-growing Arctic Willow.

The glaciers in this Canadian outpost have been rapidly disintegrating; its main Ward Hunt Ice shelf fractured a couple years ago, while another, the Markham shelf, broke off into the sea.

Beaver Pond, Ellesmere Island. Image Credit: James R. Drummond/Dalhousie University
It’s a great place to study the effects of climate change, both modern and past. Beaver Pond on Ellesmere Island is exceptionally well preserved with peat layers that contain a diverse assemblage of 4 to 5 million year old fossils from a time when the Earth was much warmer than today, and Beaver Pond teeming with life.

Researchers led by the University of Colorado and Canadian Museum of Nature have studied some of these fossils to get a more precise estimate of the Arctic temperature during that time period. It was, of course, warmer than today’s Arctic.

But what’s surprising is that the Arctic temperature was considerably warmer relative to today than global averages. In a paper they published in the most recent journal of Geology, the found that while the average global temperature during the Pliocene was 3.6 to 5.4 degrees Fahrenheit warmer than today, Arctic temperatures may have been a whopping 34 degrees balmier.

“These results indicate that Arctic temperatures may be exceedingly sensitive to anthropogenic CO2 emissions,” the researchers write.

Essentially, tropical temperatures varied a lot less than what was happening in the Arctic. This “reduced temperature gradient” can be explained by a number of mechanisms. Heat transport northward from ocean circulation is one potential warming factor, as are changes in Arctic cloud cover and greater absorption of heat due to less ice and darker waters.

What does this spell for today’s Arctic? The researchers write:

“The Arctic is clearly a bellwether for modern climate change. Arctic temperatures have increased more rapidly in response to anthropogenic greenhouse gas forcing than global temperatures … our results indicate that a significant increase in Arctic temperatures may be imminent in response to current atmospheric CO2 levels.”

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