Greenhouse Gas Mitigation Options Influence Climate via Direct Effects of Land-Use Change
Proposed climate mitigation measures do not account for the non-greenhouse gas climate impacts of land-use change such as the regional effects of changing albedo or evapotranspiration. The same is true of the stabilization targets modeled for the Fifth Climate Model Intercomparison Project (CMIP5) Representative Concentration Pathways (RCPs). A recent U.S. Department of Energy (DOE) study examined the climate implications of two different scenarios that stabilize radiative forcing by greenhouse gases and aerosols at the same level, but with dramatically different patterns of land-use change over the 21st century. The study relied on a new modeling framework, the Integrated Earth System Model (iESM) being developed by three DOE labs, which couples the human decisionmaking components of an integrated assessment model, the Global Change Assessment Model (GCAM), with the Global Land-Use Model (GLM), and a state-of-the-art global climate model, the Community Earth System Model (CESM). The iESM is able to replicate the model coupling procedure in CMIP5 and can provide insight into the importance of non-greenhouse gas climate forcing from land-use change. The study also used offline land and radiative transfer models to identify forcing and feedback mechanisms that contribute to the climate effects of land-use change in different regions. The study found that Boreal deforestation strongly influences climate due to increased albedo coupled with a regional-scale water vapor feedback. Globally, the mitigation scenario with high biofuel use and correspondingly high levels of deforestation yielded a 21st century warming trend that is 0.5 °C cooler than baseline, driven by a decrease in radiative forcing that is distributed unevenly around the globe. These results demonstrate that neither climate change nor actual radiative forcing is uniquely related to atmospheric forcing targets, but depend on the socioeconomic pathways followed to meet each target.
Jones, A. D., W. D. Collins, J. Edmonds, M. S. Torn, A. Janetos, K. V. Calvin, A. Thompson, L. P. Chini, J. Mao,
X. Shi, P. E. Thornton, G. Hurtt, and M. Wise. 2012. “Greenhouse Gas Policy Influences Climate via Direct Effects
of Land-Use Change,” Journal of Climate, DOI:10.1175/JCLI-D-12-00377.1.