forcing from these short-lived agents. In addition, the current concept is not useful for evaluating how the rate of technical transformation, which depends on economic and policy drivers, affects the trade-off between two greenhouse gases.

For most policy applications, the relationship between radiative forcing and temperature is assumed to be linear, suggesting that radiative forcing from individual positive and negative forcing agents could be summed to determine a net forcing. This assumption is generally reasonable for homogeneously distributed greenhouse gases, but it does not hold for all forcings. Thus, the assumed linearity of radiative forcing has been simultaneously useful and misleading for the policy community. It is important to determine the degree to which global mean TOA forcings are additive and whether one can expect, for example, canceling effects on climate change from changes in greenhouse gases on the one hand and changes in reflective aerosols on the other.

RECOMMENDATIONS:

Encourage policy analysts and integrated assessment modelers to move beyond simple climate models based entirely on global mean TOA radiative forcing and incorporate new global and regional radiative and nonradiative forcing metrics as they become available.

• Devise practical tools to relate new forcing metrics that may be introduced in the future to simple measures of climate change.

• Explore ways to extend the GWP concept to account for aerosols and aerosol precursors, regional variation in forcing, and economic and policy factors that might affect the long-term impact of forcings.

• Provide guidance to policy analysts on how individual radiative forcings combine to produce a net radiative forcing with an associated uncertainty.



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