Typical global climate simulations use spatial resolutions of about 300 kilometers (186 miles), which limits their ability to simulate climate and climate change on a regional scale. For example, with these lower resolutions it is difficult to assess climate changes, and the resulting societal impacts, in the climatically varying regions within California.
The high-resolution global climate simulations were run on a number of large computers at LLNL and on two machines at the Department of Energy's National Energy Research Supercomputer Center (NERSC).
The 50 km global model has 32 times more grid cells and requires about 200 times more computer processing time than comparable models at 300-km resolution.
"While higher resolutions have been used in weather prediction simulations before, those typically only cover several days," said Philip Duffy, group leader of LLNL's Climate System Modeling Group in the Atmospheric Science Division and key author of a paper on the subject. "Livermore's climate simulations span years."
A two-part paper describing the results has been submitted to Climate Dynamics. Co-authors include LLNL researchers Bala Govindasamy, Jose Milovich, Karl Taylor, Michael Wehner and Starley Thompson.
The high-resolution global climate simulations have been funded in part by the LLNL Laboratory-Directed Research and Development (LDRD) Program, and in part by the DOE's Climate Change Prediction Program.
The 50-km resolution simulations more closely mirror the present climate than do comparable coarse-resolution simulations, Duffy said. Researchers from Livermore's Program for Climate Model Diagnosis and Intercomparison (PCMDI) compared the high-resolution present climate simulations to observations and to results of simulations at coarse resolution (300 km). They found significantly more agreement between the model results and observations, indicating that increasing the resolution brings very significant improvements in the model's ability to simulate large-scale features of climate.
To show the effects of greenhouse gases on future climate, Livermore researchers ran models at 300-km and 75-km resolutions. Because they represent a possible future climate, the model results cannot be evaluated by comparing them to observations. The results indicate that globally averaged climate changes are very similar in the 75-km and 300-km models. However predicted climate changes in specific geographical regions can be very different at the finer resolution.
"Our higher resolution global climate simulations can be used to provide information on many of the most important societal impacts of climate changes, such as the impacts on waster resource management, agriculture and human health," Duffy said. "We hope to improve the realism of the models and produce better predictions of future climate on both global and regional scales."
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