Climate modeling

W.F. Spotz, P.N. Swarztrauber
2002 Computing in science & engineering (Print)  
C limate modeling is perhaps the largest computational challenge the human race has attempted to date. Only a handful of applications exist on a larger scale, and none require the same level of detail. The number of components required to work together is also unprecedented in the field of computational science: atmosphere, land, ocean, and ice models (joined by a flux coupler) must work with radiation, cloud, chemistry, advection, soil, vegetation, and water runoff models (not to mention a
more » ... e host of subgrid parameterizations) to produce meaningful results. We can simplify some of these models, depending on the question to be answered, but our climate system's complex interactions will continue to strain the limits of our largest supercomputers for the foreseeable future. Simulating the Earth's climate Because we cannot perform large-scale experiments on the Earth's climatological system, these climate models are our only laboratory for getting answers to questions about how our environment behaves and how it responds to changes-human-made or otherwise. The answers we obtain provide the foundation for debate about our ecological policies, which in turn profoundly affect how we live our lives and conduct our business. Average global temperatures are rising, and our current models support the conjecture that human activity contributes to that rise. Those who oppose policy changes that would address this conclusion point to the inaccuracies in current models to dismiss the results. Implicit in this dismissal is the assumption that the errors bias results toward a warmer climate. However, even if we choose to ignore collective scientific and model predictions, we cannot ignore the warming trend and the commonsense conclusion that humans are likely contributors. In any event, between humans and nature, only humans can intentionally attempt to reduce the warming trend. To that end, climate models provide a relatively new and extremely valuable tool. The development of climate models, especially the atmospheric component, is somewhat unique in the field of numerical modeling. Most computational fluid dynamicists are surprised to learn, for example, that almost all productionlevel atmospheric models are based on a spectral expansion, not the more common finite volumes or finite elements. Spectral approximations are rarely even considered for most other applications, because they are simply unworkable for most geometries. The atmosphere's geometry, however, is a simple spherical shell, its natural coordinate system is spherical, and the spherical coordinate system has built-in singularities at the poles. For example, the total derivative of the velocity is infinite at the poles. No approach handles these singularities as elegantly as the spherical harmonic spectral transform method. Also, when spectral models came to dominate, the most powerful computers consisted of vector processors-and the spectral method vectorizes beautifully. Computer chip design is dictated by market
doi:10.1109/mcise.2002.1032425 fatcat:oxegcy226rhytozxssugufohqy