Mar 21, 2012

Framing the way to relate climate extremes to climate change

Kevin E. Trenberth
Climatic Change
  • States that SSTs have risen by 0.5–0.6 °C since the 1950s, and over the oceans this has led to 4 % more water vapor in the atmosphere since the 1970s
  • States that, as a result of rising SSTs and water vapor over the oceans, the air is on average warmer and moister than it was prior to about 1970 and in turn has likely led to a 5–10 % effect on precipitation and storms that is greatly amplified in extremes
  • States the atmospheric and ocean environment has changed from human activities in ways that affect storms and extreme climate events
  • States a small shift in the mean can lead to very large percentage changes in extremes
  • States anthropogenic global warming inherently has decadal time scales and can be readily masked by natural variability on short time scales
  • States that to the extent that interactions are linear, even places that feature below normal temperatures are still warmer than they otherwise would be
  • States that it is when natural variability and climate change develop in the same direction that records get broken
  • Discusses, as an example, how the rapid transition from El Niño prior to May 2010 to La Niña by July 2010 along with global warming contributed to the record high sea surface temperatures in the tropical Indian and Atlantic Oceans and in close proximity to places where record flooding subsequently occurred
  • Provides a commentary on recent climate extremes
  • Says the answer to the oft-asked question of whether an event is caused by climate change is that it is the wrong question; rather, all weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be