A matter of scale

shadow-300January 27, 2011

Many climate models lack the resolution to see the full range of impacts from a warmer world.

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Jan. 27: New data suggests feds understate climate costs

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By Douglas Fischer and Nicole Heller 

Daily Climate and Climate Central

Global climate models are enormously complex mathematical endeavors. To keep them manageable, scientists chop the Earth into large grids to track impacts. Some models use grids the size of continents; others can be as small as 150 square kilometers. 

A two-week heat wave can be devastating. But it gets masked in many climate models.

Either way, however, the large-scale resolution means that many important regional and local impacts effectively disappear.

University of California, Berkeley, economist Michael Hanemann has attempted to refine the resolution to examine the economic impacts of climate change in far smaller chunks of property. As he downscales to a 12-square-kilometer grid to look at impacts within California, for instance, he finds that damages - and uncertainties - increase precipitously.

Take temperature increases. A model might show an average increase of 2ºC across an entire continent - a harmless enough jump. But that average might in reality reflect a slight 0.5º increase on the coasts and a more consequential 3º or 4º increase mid-continent - a far different beast entirely.

The same is true with time scales, Hanemann noted. A two-week heat snap can be devastating to both lives and livelihoods - for some crops even a few days of heat above 90ºF kills the season. But that kind of heat can get masked in a model using monthly averages.

"The more I've looked into the literature and talked to physical scientists, the more evident it is that most of the damage is done during extreme events," Hanemann said. But they are largely invisible to many economic models using broad spatial and temporal scales.

"Running (a climate model) on a daily time stamp is a massive computing problem, so it's understandable why they do what they do," he added. 

"But this significantly understates things." 

Douglas Fischer is editor of DailyClimate.org, a nonprofit news service covering climate change. 

Nicole Heller is a research scientist at ClimateCentral.org, a nonprofit, nonpartisan media organization comprised of earth scientists and science journalists.

Photo of shadow on cracked earth in Colombia courtesy Neil Palmer/Int'l Center for Tropical Agriculture

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 Based on a work at www.dailyclimate.org