Science Source

David J. Karoly, Karl Braganza, Peter A. Stott, Julie M. Arblaster, Gerald A. Meehl, Anthony J. Broccoli, Keith W. Dixon

Science

Published date November 14, 2003

Detection of a Human Influence on North American Climate

Uses several indices of large-scale patterns of surface temperature variation to investigate climate change in North America over the 20th century
Simulates the observed variability of these indices using a number of climate models
Comparison of index trends in observations and model simulations shows that North American temperature changes from 1950 to 1999 were unlikely to be due to natural climate variation alone
Finds that observed trends over this period are consistent with simulations that include anthropogenic forcing from increasing atmospheric greenhouse gases and sulfate aerosols
Finds, however, that most of the observed warming from 1900 to 1949 was likely due to natural climate variation