Climate Change Simulations with CCSM & CESM

Key Challenges: Perform fundamental research on the processes that influence the natural variability of Earth’s climate system and relate those processes to possible future manifestations of anthropogenic climate change. This work utilizes an emerging class of Earth System Models that include detailed physical, chemical, and biological processes as well as interactions and feedbacks in the atmosphere, oceans, and land surface, to carry out policy-relevant adaptation/mitigation scenarios. This involves using CCSM3.5 and CCSM4 at resolutions higher than ever possible before.

Why it Matters: These studies will provide data for the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5). The 2007 IPCC AR4 report, a breakthrough study that enjoyed broad public acceptance, presented a clear picture of a planet undergoing rapid human-induced climate transition with significant societal and environmental impacts. Now, however, the basic question being asked by society is, what is the local, time-evolving nature of climate change to which we must adapt and can these climactic changes be mitigated?

Accomplishments: Simulations have investigated the impact of rapid release of Arctic water into the Pacific and its association with the collapse of the Meridional Overturning Circulation (MOC) that may have been related to abrupt climate changes that occurred in the last glacial period. NERSC studies have shown that the MOC has two stable equilibrium states only if the Bering Strait, a shallow and narrow seaway connecting the Pacific with the Arctic, is closed. With an open Bering Strait, the MOC does not show any hysteresis behavior. This research is potentially significant to explain why the abrupt climate change events only occurred in certain period of the last glacial time, but not in the Holocene. Other studies have conclusively shown that the threat of global warming can still be greatly diminished, saving arctic ice and reducing sea level rise, if we can achieve significant cuts in the emissions of greenhouse gases during this century.

A high resolution simulation, using the finite volume version of NCAR's Community Atmosphere Model, showing how well the model can reproduce observed tropical cyclone statistics. Simulated storms are generated spontaneously from the model's simulated weather conditions long after the memory of initial conditions have been forgotten. The structure of these simulated tropical cyclones is surprisingly realistic.

NERSC Climate Earth System Grid Gateway: http://esg.nersc.gov/esgcet/home.htm

Investigators: Warren Washington, Lawrence Buja, and Jerry Meehl, National Center for Atmospheric Research

More Information: See "Predictability of Atlantic overturning circulation and associated surface patterns in two CCSM3 large ensemble experiments," 15th Annual CESM Workshop (2010);
Geophysiccal Research Letters, 36 L08703 (2009); and the The Community Earth System Model web site.