Weather and Climate Extremes

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.

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One thought on “Weather and Climate Extremes

  1. Hi Max,

    I like your blog about the weather. I discovered it late last year and, after going inactive for most of the winter and spring, am glad to see you have resumed adding entries on a regular basis. Since you have a far richer background and expertise than just general meteorology, I think you’re well-qualified to share your educated opinion with your readers.

    With your most recent posting about global warming and tropical storms, I found this summary statement from the report you reference to be a bit dubious:

    “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.”

    Is it really a foregone conclusion that global warming is being caused by human activity vs. other explainable natural phenomena? Is the science veto-proof on this conclusion, or is it still in the discovery phase? In light of the evidence than some weather scientists say active tropical storm activity tends to run for periods of a decade or two then quiet down, does it make sense to blame the current up tick in activity on global warming? Or to minimize the fact that storms like Andrew in 1992 and Katrina in 2005 did not cause so much damage because they were exceptionally powerful, but instead because so many more people were living in harm’s way than in past years? I would very much like to get your thoughts, again because you certainly have more expertise here than many of your contemporaries who dabble in weather blogs.

    Thanks for reading my note. Thanks also for picking up the pen — or at least the digital equivalent — and sharing your expertise about weather and tropical storms with us readers at large who find weather interesting, but don’t have the knowledge or training to understand the finer points about why a thunderstorm suddenly builds to cut our fishing trip short, or why the evening sea breeze refreshes us after a hot day at the beach.

    Keep up the great work!

    – Brian

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