Continue observations of climate forcings and variables without interruption for the foreseeable future in a manner consistent with established climate monitoring principles (e.g., adequate cross-calibration of successive, overlapping datasets).
Develop the capability to obtain benchmark measurements (i.e., with uncertainty significantly smaller than the change to be detected) of key parameters (e.g., sea level altimetry, solar irradiance, and spectrally resolved, absolute radiance to space).
Conduct highly accurate measurements of global ocean heat content and its change over time.
Establishing relationships between past climate changes and known natural and anthropogenic forcings provides information on how such forcings may impact large-scale climate in the future. Instrumental records extend back about 150 years at best. Comparisons of observed surface temperatures with those simulated using reconstructions of the past forcings have yielded important insights into the roles of various natural and anthropogenic factors governing climate change. However, the shortness of the instrumental record limits the confidence with which climate change since preindustrial times can be attributed to specific forcings. Proxy records obtained from ice cores, sediments, tree rings, and other sources provide a critical tool for extending knowledge of forcings and effects further back in history. The lack of proxy climate data in certain key regions is a major limitation. Such regional information is important in evaluating the potential roles of changes in modes of climate variability, such as the El Niño/ Southern Oscillation (ENSO).
Develop a best-estimate climate forcing history for the past century to millennium.
Using an ensemble of climate models, simulate the regional and global climate response to the best-estimate forcings and compare to the observed climate record.
The interaction between aerosols and clouds can lead to a number of indirect radiative effects that arguably represent the greatest uncertainty in current radiative forcing assessments. In the so-called first indirect aerosol