NERSC Initiative for Scientific Exploration (NISE) 2009 Awards

Determining the time-varying impact of cloud-aerosol interactions during the 20th century

Tom Bettge, National Center for Atmospheric Research

Sponsoring NERSC Project: Climate Change Simulations with CCSM: Moderate and High Resolution Studies (mp9), Principal Investigator: Warren Washington, National Center for Atmospheric Research

The largest uncertainty in the forcing of climate during the 20th century from the most recent IPCC report is the indirect effect of enhanced cloud-aerosol interactions. These experiments will enable a more quantitative assessment of the potential cooling from this process and to what extent they offset the warming impacts of elevated greenhouse gases to date and how these impacts may change in a future climate.

Process studies indicate that the dominant impact of elevated atmospheric aerosols on clouds is a cooling of the earth system due to brighter low clouds and increased reflection of solar radiation. However, the role of this process in the time-evolving climate system remains uncertain. This research will use a development version of CCSM that utilizes cutting edge aerosol and cloud physics that can represent the climate impacts of cloud-aerosol interactions. These high impact experiments will enable a more quantitative assessment of the potential cooling from this process and to what extent they offset the warming impacts of elevated greenhouse to date and how these impacts may change in a future climate.