Field Notes: The Polar Field Services Newsletter

Improved Climate Model Released By NCAR

Modeling climate’s complexity: This image, taken from a larger simulation of 20th century climate, depicts several aspects of Earth’s climate system. Sea surface temperatures and sea ice concentrations are shown by the two color scales. The figure also captures sea level pressure and low-level winds, including warmer air moving north on the eastern side of low-pressure regions and colder air moving south on the western side of the lows. Such simulations, produced by the NCAR-based Community Climate System Model, can also depict additional features of the climate system, such as precipitation. Companion software, recently released as the Community Earth System Model, will enable scientists to study the climate system in even greater complexity. Image courtesy UCAR

The latest version of Boulder’s National Center for Atmospheric Research Community Earth System Model (CESM) includes for the first time ever the capability to project how climate change will affect the ice sheets covering Antarctica and Greenland. The model, released August 17, will be one of the primary climate models used for the next assessment by the Intergovernmental Panel on Climate Change (IPCC). It replaces a version of the same model released in 2004.

Specifically, the new model’s advanced capabilities will help scientists better understand some of the critical mysteries of global climate change, including:

• What impact will warming temperatures have on the massive ice sheets in Greenland and Antarctica?

• How will patterns in the ocean and atmosphere affect regional climate in coming decades?

• How will climate change influence the severity and frequency of tropical cyclones, including hurricanes?

• What are the effects of tiny airborne particles, known as aerosols, on clouds and temperatures?

Available On The Web

The CESM is one of about a dozen climate models worldwide that can be used to simulate the many components of Earth’s climate system, including the oceans, atmosphere, sea ice, and land cover. The CESM and its predecessors are unique among these models; a broad community of scientists developed them. The model is free to researchers worldwide and can be downloaded here.

“With the Community Earth System Model, we can pursue scientific questions that we could not address previously,” says NCAR scientist James Hurrell, chair of the scientific steering committee that developed the model. “Thanks to its improved physics and expanded biogeochemistry, it gives us a better representation of the real world.”

How Models Work

Climate models, like weather models, rely on a three-dimensional mesh that reaches high into the atmosphere and into the oceans. At regularly spaced intervals, or grid points, the models use laws of physics to compute atmospheric and environmental variables, simulating the exchanges among gases, particles, and energy across the atmosphere.

Because climate models cover far longer periods than weather models, they cannot include as much detail. Thus, climate projections appear on regional to global scales rather than local scales. This approach enables researchers to simulate global climate over years, decades, or millennia. To verify a model’s accuracy, scientists typically simulate past conditions and then compare the model results to actual observations.

Improved Forecasts

Using the CESM, Hurrell and other scientists hope to learn more about ocean-atmosphere patterns such as the North Atlantic Oscillation and the Pacific Decadal Oscillation, which affect sea surface temperatures as well as atmospheric conditions. Such knowledge, Hurrell says, can eventually lead to forecasts spanning several years of potential weather impacts, such as a particular region facing a high probability of drought, or another region likely facing several years of cold and wet conditions.  —Rachel Walker

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