PNAS Proceedings of the National Academy of Sciences of the United States of America
Reconciling anthropogenic climate change with observed temperature 1998?2008
1. Robert K. Kaufmanna,1, 2. Heikki Kauppib, 3. Michael L. Manna, and 4. James H. Stockc
+ Author Affiliations
1. aDepartment of Geography and Environment, Center for Energy and Environmental Studies, Boston University, 675 Commonwealth Avenue (Room 457), Boston, MA 02215; 2. bDepartment of Economics, University of Turku, FI-20014, Turku, Finland; and 3. cDepartment of Economics, Harvard University, 1805 Cambridge Street, Cambridge, MA 02138
1.
Edited by Robert E. Dickinson, University of Texas at Austin, Austin, TX, and approved June 2, 2011 (received for review February 16, 2011)
Abstract
Given the widely noted increase in the warming effects of rising greenhouse gas concentrations, it has been unclear why global surface temperatures did not rise between 1998 and 2008. We find that this hiatus in warming coincides with a period of little increase in the sum of anthropogenic and natural forcings. Declining solar insolation as part of a normal eleven-year cycle, and a cyclical change from an El Nino to a La Nina dominate our measure of anthropogenic effects because rapid growth in short-lived sulfur emissions partially offsets rising greenhouse gas concentrations. As such, we find that recent global temperature records are consistent with the existing understanding of the relationship among global surface temperature, internal variability, and radiative forcing, which includes anthropogenic factors with well known warming and cooling effects.
