Division Director’s Message

Scientists in the Climate and Global Dynamics (CGD) Division and collaborators have spent much of the past year improving the Community Climate System Model (CCSM). Improvements have been made in all components of the model: atmosphere, land, ocean and sea ice. This new version of the model, to be called CCSM3, will be used for a wide variety of studies concerning climate variability and climate change. The most extensive set of simulations will be climate change scenarios, the data from which will be submitted to the 4^th Report of the Intergovernmental Panel on Climate Change (IPCC). We expect CCSM3 to be major contributor to this activity.

One of the major issues in climate change modeling is the difference in the magnitude of the response of different models to the same increase in concentration of greenhouse gases. The amount of global temperature increase per unit increase in forcing (by a greenhouse gas or gases) is called climate sensitivity. This number ranges from 1.5 to 4.5 degrees (centigrade) for doubling of carbon dioxide. Clearly, policy makers want and need to have a greatly reduced uncertainty in climate sensitivity in order to decide how to address climate change issues. CGD scientists are working with scientists from other modeling groups to find out what determines climate sensitivity and why the various models give the different results that they do. One preliminary result relates climate sensitivity to atmospheric water concentrations and modeled cloud processes. These are parts of the models that are highly parameterized and subject to substantial uncertainty. This suggests that focused research and diagnosis might be needed in the future to reduce the uncertainty in the model parameterizations and the resulting climate sensitivity.

CGD scientists and collaborators are also adding a new biogeochemistry component to the CCSM. The land surface model will include exchange of carbon with the atmosphere, which will allow plants to grow or die. The ocean model will take carbon from the atmosphere and model the growth of organisms that in turn will precipitate carbon to the ocean floor. The atmosphere will move carbon dioxide around with the winds. This group of coupled components will allow us to investigate factors that determine the carbon cycle of the earth and hopefully will give us a more accurate estimate of the growth of carbon dioxide in the atmosphere. The carbon cycle work will be augmented soon by the addition of a nitrogen cycle and iron fertilization by atmospheric dust, as well. (Nitrogen and iron will affect the growth rates of plants and ocean organisms and thus change the carbon cycle transformation rates.) Results from these experiments will also be contributed to the 4^th IPCC Report.

CGD scientists are also participating in several of the new NCAR Strategic Initiatives, including Data Assimilation, Water Cycle Across Scales, Biogeosciences (see above), and Climate Assessments. We have already seen some excellent results from this work and we expect further accomplishments to come from these projects. We are pleased play important roles in these exciting new interdisciplinary projects within NCAR.