Nov 1, 2007

Human Contribution to the Lengthening of the Growing Season during 1950–99

Nikolaos Christidis, Peter A. Stott, and Simon Brown
AMS Journal of Climate
  • Carries out an optimal detection analysis to assess the significance of increases in the growing season length during 1950–99, and to measure the anthropogenic component of the change
  • Finds the signal is detectable, both on global and continental scales, and human influence needs to be accounted for if it is to be fully explained
  • Finds the change in the growing season length is asymmetric and largely due to the earlier onset of spring, rather than the later ending of autumn
  • Finds that the growing season length, based on exceedence of local temperature thresholds, has a rate of increase of about 1.5 days decade−1 over the observation area
  • Finds that local variations also allow for negative trends in parts of North America
  • The analysis suggests that the signal can be attributed to the anthropogenic forcings that have acted on the climate system and no other forcings are necessary to describe the change
  • Model projections predict that under future climate change the later ending of autumn will also contribute significantly to the lengthening of the growing season, which will increase in the twenty-first century by more than a month
  • Concludes that such major changes in seasonality will affect physical and biological systems in several ways, leading to important environmental and socioeconomic consequences and adaptation challenges