Parallel Processing Allows Faster, More Detailed Climate Modeling

In the past 10 years, as scientists have achieved a better understanding of the Earth's climate, the computer industry has developed ever-more-powerful machines. These two factors are now resulting in increasingly accurate computer modeling tools for studying and predicting climate change. Some important results are coming from the partnership between NERSC and climate modeling experts at the National Center for Atmospheric Research (NCAR) in Colorado.

Collaborating scientists at NCAR, the Naval Postgraduate School, and Los Alamos National Laboratory are able to run their Parallel Climate Model with High Resolution Ocean and Sea Ice (PCM) faster than ever on NERSC's T3E-900. Running PCM on an older model supercomputer, such as a 16-processor Cray C90, would require more than 10 hours to simulate one year, or more than three months of computer time to model a century. Using half of the 512 processors of NERSC's T3E-900, the same model can be run 28 times faster. The entire model could not even be loaded on smaller systems.

"The performance NCAR has achieved is unmatched by other climate codes in the United States," said NERSC Division Director Horst Simon. "The NCAR team has demonstrated that production climate research can be carried out on a parallel processing, distributed memory supercomputer. Not only does NCAR's code run well on our machine, but its design also allows it to be scaled up for creating an even more powerful model in the future."

Warren Washington of NCAR, principal investigator on the project, and his colleagues are investigating the effect of greenhouse gas increases and sulfate aerosols on global warming. While increased greenhouse gases cause global warming, sulfate aerosols cause less warming, and in some cases, regional cooling.

It is the capability of running the ocean and sea ice components that makes PCM so useful, according to Washington. The higher the resolution for such features as the Gulf Stream or Kurioshio Current, the more accurately their role can be included as transporters of heat and salt.

Just as one year's weather cannot be interpreted as evidence of climate change, one computerized model cannot produce definitive answers. Instead, researchers need to run a series of different modeling experiments to take into account differing possible future climate scenarios. "We need to know if the change is statistically significant in order to confidently answer the questions being asked by policymakers," Washington says. More powerful computers allow these simulations to be researched at higher resolution.