The U.S. Climate Change Science Program and the Subcommittee on Global Change Research has recently released a scientific assessment that provides the first comprehensive analysis of observed and projected changes in weather and climate extremes in North America and U.S. territories. The Intergovernmental Panel on Climate Change previously evaluated extreme weather and climate events on a global basis. However, there has not been a specific assessment across North America prior to this report.
The final report can be downloaded from http://downloads.climatescience.gov/sap/sap3-3/sap3-3-final-all.pdf. The Executive Summary states “It is well established through formal attribution studies that the global warming of the past 50 years is due primarily to human-induced increases in heat-trapping gases.” The report gives a good explanation of weather extremes in general and why they are important. However, given that this is a hurricane blog, I will restrict comments to Hurricanes and Tropical Storms.
The report states “It is very likely that the human-induced increase in greenhouse gases has contributed to the increase in sea surface temperatures in the hurricane formation regions. Over the past 50 years there has been a strong statistical connection between tropical Atlantic sea surface temperatures and Atlantic hurricane activity as measured by the Power Dissipation Index (which combines storm intensity, duration, and frequency). This evidence suggests a human contribution to recent hurricane activity. However, a confident assessment of human influence on hurricanes will require further studies using models and observations, with emphasis on distinguishing natural from human-induece changes in hurricane activity through their influence on factors such as historical sea surface temperatures, wind shear, and atmospheric vertical stability.”
The report is careful to note that there have been natural fluctuations in the number of tropical storms and huricanes from decade to decade and data uncertainty is larger in the early part of the record compared to the satellite era beginning in 1965. In addition, there is no observational evidence for an increase in North American mainland landfalling hurricanes since the late 1800s.
The report is well worth reading for information on weather and climate extremes in North America and U.S. territories. And don’t just read the hurricane sections.