Is Radiative Forcing Between Land-Use Change and Greenhouse Gases Additive?
A recent U.S. Department of Energy study by researchers from Lawrence Berkeley National Laboratory sought to determine how land-use change responds to increasing greenhouse gas forcing, from both regional and global climate change perspectives. The researchers found that predictions based on net radiative forcing are inaccurate. In particular, the study examined an idealized scenario in which positive forcing from greenhouse gases is balanced by an approximately equal magnitude of negative forcing from conversion of natural vegetation to agriculture. If forcings from land-use change and greenhouse gases can be treated as perfectly balanced, very little climate change would be expected in this nearly neutral forcing scenario. However, the study found widespread significant changes in temperature, precipitation, and atmospheric circulation. Furthermore, the land-use change climate response occurred on a much faster timescale than the greenhouse gas climate response, implying a significant imbalance between greenhouse forcing and negative forcings associated with land-use change. While this study challenges the utility of combining radiative forcing from substantially different climate drivers like land-use change and greenhouse gases, it did find that spatially resolved climate responses of individual forcings could be combined linearly to reproduce their joint climate effect. That is, while the forcing values themselves are not additive in a meaningful way, their climate responses appear to be additive. This final result suggests an alternative approach for climate change assessment protocols that currently rely on a measure of net radiative forcing to determine climate outcomes of different socioeconomic, technology, and policy scenarios.
Jones, A. D., W. D. Collins, and M. S. Torn. 2013. “On the Additivity of Radiative Forcing Between Land-Use Change and Greenhouse Gases,” Geophysical Research Letters 40 , 4036–41. DOI: 10.1002/grl.50754.