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


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