Statement to the US Commission on Ocean Policy Understanding the Ocean’s Role in Climate Roger Lukas Department of Oceanography School of Ocean and Earth Science and Technology University of Hawaii May 6, 2002 Introduction This statement summarizes the present understanding of the roles of the oceans in climate, including the oceanic impacts of climate variability and change. Areas where additional research is required are identified. Issues that are of particular relevance for the Pacific Region are noted. The programmatic context for US ocean climate research is considered. Recommendations are made to: • Enhance sustained ocean observations, • Enhance ocean process research to improve numerical models for ocean-state estimation and forecasting, and • Develop mechanisms to improve both inter-agency and inter-program cooperation and coordination in ocean climate research The Ocean’s Role in Climate Because of its huge heat capacity and carbon reservoir, the ocean plays a central role in the Earth’s climate system. The essential climate-related characteristics of the ocean are that • it stores and releases large quantities of heat, freshwater and soluble gases, • heat, freshwater and gas releases are sometimes substantially separated in space and time from their point of storage, due to ocean dynamics and mixing • freshwater and gas fluxes are determined partly by direct and indirect effects of ocean surface temperatures • carbon fluxes, storage and natural sequestration depend on highly complex biogeochemistry and marine ecosystems dynamics These characteristics include the integrating (buffering) effect of the ocean, which emphasizes low frequency variations of heat and carbon and delays these signals in time. They also include remote forcing and delays due to slow internal wave propagation and slow transport by currents. Such lags are important for switching the signs of ocean temperature anomalies and for developing coupled oscillations.