|Rotation tracks detected by NWS Doppler radars on 27 April.|
Source: NOAA/National Weather Service.
Dr. Martin Hoerling of the Earth Systems Research Laboratory recently posted a preliminary discussion of some of the issues above and an assessment of the event in terms of climate trends since 1979. He highlights the following conclusions from the IPCC and US Climate Change Synthesis Report, which echo some of the concerns above:
"There is insufficient evidence to determine whether trends exist in...small-scale phenomena such as tornadoes, hail, lightning and dust-storms" - IPCC AR4
"The data used to examine changes in the frequency and severity of tornadoes and severe thunderstorms are inadequate to make definitive statements about actual changes" - US Climate Change Synthesis Report SAP 3.3
These statements reflect the current scientific consensus on the topic. The 25-28 April event was extraordinary, but individual events of this type result from intrinsic weather variability. Whether or not trends in the frequency or intensity of such events exist and are related to anthropogenic climate change is an issue that requires further research.