The events of yesterday across Massachusetts are horrific and extreme, but it’s not so clear whether they are related to climate change, or how to definitely assign cause and effect either way. A good reference on the historical trends of many weather events (but not tornadoes) in the U.S. and how they may or may not be associated with climate change is Trends in U.S. Climate during the Twentieth Century, published by the journal Consequences: The Nature and Implications of Environmental Change. Authors Thomas R. Karl, Richard W. Knight, David R. Easterling, Robert G. Quayle, all on the scientific staff of the National Oceanic and Atmospheric Administration’s National Climatic Data Center (NCDC), in Asheville, North Carolina, analyze climate data drawn from the Center, which manages all U.S. atmospheric data that have been recorded since the advent of scientific instruments.
A second report (Weather and Climate Extremes in a Changing Climate. Regions of Focus: North America, Hawaii, Caribbean, and U.S. Pacific Islands. A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. [Thomas R. Karl, Gerald A. Meehl, Christopher D. Miller, Susan J. Hassol, Anne M. Waple, and William L. Murray (eds.)]. Department of Commerce, NOAA’s National Climatic Data Center, Washington, D.C., USA, 164 pp.) also does not make a definite statement about possible linkage between tornadoes and climate change:
An easy-to-read two-page brochure based on this report includes a nice table of “human activity” and probable links to various other categories of weather events (precipitation, heat, drought, etc).
The bottom line of much of the research comes down to this (excerpted from the above-referenced brochure):
As the climate has warmed, primarily due to human activities, we have also seen a variety of changes in extremes. [One example] of extremes that have an identifiable cause:
Human-induced warming has likely caused much of the average temperature increase in North America over the past fifty years and, consequently, changes in temperature extremes. For example, the effect of human-induced emissions of greenhouse gases has been associated with the very hot year of 2006 in the U.S.