Since these recommendations were not communicated to the July 21, 2001 U.S. Senate Committee Hearing on “Climate Change Science and Economics”, I have reproduced without comment, text from Chapter 7 in the report which starts at http://www.nap.edu/books/0309095069/html/144.html.
The current global mean top-of-the-atmosphere (TOA) radiative forcing concept with adjusted stratospheric temperatures has been used extensively in the climate research literature over the past few decades and has also become a standard tool for policy analysis endorsed by the Intergovernmental Panel on Climate Change (IPCC). It is a useful index for estimating global average surface temperature change resulting from changes in well-mixed greenhouse gases, solar irradiance, surface albedo, and non-absorbing aerosols. The relative ease of calculating radiative forcing and the associated temperature response has enabled the use of climate models, simpler versions of those models, and chemical transport models to investigate the many factors that may influence climate. In short, the TOA radiative forcing concept still has considerable value and should be retained as a standard metric in future climate research.
Nonetheless, the traditional radiative forcing concept has major limitations that have been revealed by recent research on non-conventional forcing agents and regional studies. It is limited in its ability to describe the climate effects of absorbing aerosols, aerosol interactions with clouds, ozone, land-surface modification, and surface biogeochemical effects. Also, it diagnoses only one measure of climate change: equilibrium response of global mean surface temperature. It does not provide information on nonradiative climate effects, spatial or temporal variation of the forcing, or nonlinearity in the relationship between forcings and surface temperature response. Recent extensions of the concept that allow surface temperatures to adjust have refined the radiative forcing concept to address deficiencies in the original approach. Although currently applied to global mean conditions, this method could be extended for regional conditions.
The strengths of the traditional radiative forcing concept warrant its continued use in scientific investigations, climate change assessments, and policy applications. At the same time, its limitations call for using additional metrics that account more fully for the nonradiative effects of forcing, the spatial and temporal heterogeneity of forcing, and nonlinearities. The committee believes that these limitations can be addressed effectively through the introduction of additional forcing metrics in climate change research and policy. This chapter provides several recommendations for extending the traditional radiative forcing concept in the scientific and policy arenas. It identifies research needed to improve quantification and understanding of different forcings and their impacts on climate, to better inform climate policy discussions, and to obtain reliable observations of climate forcings and responses in the past and future. A large number of recommendations are provided because many research avenues need to be explored in order to improve understanding of climate forcings.
The text continues at http://www.nap.edu/books/0309095069/html/145.html.