Thursday, March 29, 2012

IPCC Speaks on Weather and Climate Extremes

The Intergovernmental Panel on Climate Change (IPCC) has just released a Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (a.k.a. SREX).  The Summary for Policy Makers and Full Report are available here.  Ignore the press coverage and go straight to the source.  

I haven't had a chance to fully peruse the report, which is more than 500 pages long (surely you will all consume and digest this by tonight).  However, since we have been talking the past week about heat waves and snow records, I thought I would summarize some of the key findings with regards to trends in extreme events:
  •  "There is evidence in observations gathered 1950 of change in some extremes. Confidence in observed changes in extremes depends on the quality and quantity of data and the availability of studies analyzing these data, which vary across regions and for different extremes."
  • "It is very likely that there has been an overall decrease in the number of cold days and nights, and an overall increase in the number of warm days and nights, at the global scale, that is, for most land areas with sufficient data."
  • "In many (but not all) regions over the globe with sufficient data, there is medium confidence that the length or number of warm spells or heat waves has increased."
  • "There have been statistically significant trends in the number of heavy precipitation events in some regions. It is likely that more of these regions have experienced increases than decreases, although there are strong regional and subregional variations in these trends."
  • "There is low confidence in any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity (i.e., intensity, frequency, duration), after accounting for past changes in observing capabilities. 
  • "It is likely that there has been a poleward shift in the main Northern and Southern Hemisphere extratropical storm tracks."
  • "There is low confidence in observed trends in small spatial-scale phenomena such as tornadoes and hail because of data inhomogeneities and inadequacies in monitoring systems."
My take is that is a pretty good summary of current understanding given limitations in observational datasets.  Note how the confidence is higher for those phenomenon for which we have good understanding and observations (e.g., temperature) and lower where there is insufficient data or understanding to adequately assess or evaluate trends (e.g., hurricanes and tornadoes).   They also note that there are regional variations in the quality of data and depth of analysis.  We see this even within the western United States where our understanding of climate is stronger on the Pacific coast, in part because of the strength and number of climate groups in California, Oregon and Washington, compared  to the Intermountain West.  


  1. My layman thoughts based on 50 years of skiing the Wasatch, the powder is getting heavier, the rain snow line is getting higher and there are many more high altitude rain events. It makes getting the "Utah" powder day that much more competitive.

  2. Lack of data is a main reason why we can't test your hypothesis. We need observations in the lower elevations and unfortunately those are largely uninstrumented in the Wasatch Mountains for snowpack observations. In addition, if a trend is detected, one has to do a study to establish the causes for that trend and there are many (e.g., land-surface change, dust, global warming etc.). It's tough being a scientist these days!