U. study substantiates computer models for global warming

By Brian Maffly
The Salt Lake Tribune

Computer models used to predict climate change are remarkably accurate when measured against actual weather, according to a new study by University of Utah meteorologists.  The findings are expected to boost the role of such models in shaping public policy to confront the menacing specter of global warming, generally believed to be caused by rising concentrations of atmospheric carbon from fossil fuel-burning industries.

"The best models are now capable of simulating present-day climate with accuracy approaching conventional atmospheric observations," said Thomas Reichler, a U. professor whose study appears in Bulletin of the American Meteorological Society. "These advancements will enhance public credibility of model predictions and help to justify the development of even better models."   Most climate scientists agree that computer models imperfectly account for important climate processes, such as clouds and aerosols, which have competing effects on climate and confound model accuracy. On the one hand, clouds and particles suspended in the atmosphere cool by reflecting solar radiation back into space. On the other, they have an insulating effect.

"It's a young a science," Reichler conceded. Because of our incomplete understanding of climate, models must be built on simplifying assumptions. Consequently, some have argued that model-based climate projections are too unreliable to guide public policy.   So Reichler and colleague Junsu Kim, a graduate research assistant, set out to measure the agreement between an entire generation of modeled climate projections and weather observations, examining some 55 models developed over the past 20 years.

The models simulate past, present and future climate. Since we don't know what will happen in the future or what happened with climate 100 years ago, we decided to focus on the present," Reichler said. "We saw that models developed five, 10, 15 years ago get progressively worse the older they get."

Improvements in climate modeling came about from faster computing and advancements in the understanding of climate and atmospheric physics, said meteorologist Tom Delworth of the National Oceanic and Atmospheric Administration.  Delworth leads the team that helped build the model that Reichler identified as the most accurate. This model is called "CM2.1," meaning it is the second generation of NOAA's "coupled" model, completed in 2004 and used by the International Panel on Climate Change for its Nobel Peace Prize-winning report on global warming.

"By increasing computer power we can make the grid cells smaller. That gives us more resolution for mountains and coastlines, things that impact climate," Delworth said.  The model predicts average overland temperature increases of between 5 to 7 degrees Fahrenheit by the end of the century, with more extreme shifts at higher latitudes.  "We have a clear warming trend coming, reducing Arctic ice, reduction of rainfall in the Southwest, rising sea levels," Delworth said.  His group is at work building a third version of the NOAA model, to be completed in time to contribute to the IPCC's next assessment report due in 2013.