New paper questions simplistic radiative forcing assumptions of the IPCC

A new paper published in Geophysical Research Letters finds it is incorrect to assume that radiative forcing from greenhouse gases can be added to negative radiative forcing from agricultural expansion to determine climate change. According to the authors, "when negative forcing from agricultural expansion is approximately balanced by a radiatively equivalent increase in atmospheric carbon dioxide, significant changes in temperature, precipitation, and the timing of climate change result. These idealized experiments demonstrate the non-additivity of radiative forcing from land use change and greenhouse gases and point to the need for new climate change metrics or the development of climate policies and assessment protocols that do not rely on single dimensional metrics." The IPCC projections and climate models use this simplistic assumption, which this paper has now demonstrated to be incorrect.

On the additivity of radiative forcing between land use change and greenhouse gases

Andrew D. Jones 1,*, William D. Collins 1,2,Margaret S. Torn 1,3

In scientific and policy contexts, radiative forcing—an external change in Earth's mean radiative balance—has been suggested as a metric for evaluating the strength of climate perturbations resulting from different climate change drivers such as greenhouse gases and surface physical effects of land use change. However, the utility of this approach has been questioned given the spatially concentrated and sometimes nonradiative nature of land use climate disturbances. Here we show that when negative forcing from agricultural expansion is approximately balanced by a radiatively equivalent increase in atmospheric carbon dioxide, significant changes in temperature, precipitation, and the timing of climate change result. These idealized experiments demonstrate the nonadditivity of radiative forcing from land use change and greenhouse gases and point to the need for new climate change metrics or the development of climate policies and assessment protocols that do not rely on single dimensional metrics.