 Complete the following phrase:  Richels has served on a number of national and international advisory panels, including committees of the Department of Energy, the Environmental Protection Agency, and the National Research Council. He served as an expert witness at the Department of Energys hearings on the National Energy Strategy and testified at Congressional hearings on priorities in global climate change research. He was a lead author for the Intergovernmental Panel on Climate Change IPCC Second, Third and Fourth Assessment Reports the IPCC shared the 