Hot, then cold!

A long and severe cold snap across much of the Eastern U.S. has caused considerable damage to peach and berry crops, canceled numerous baseball games, and brought up to four feet of snow to Michigan's Upper Peninsula. Here in Southeast Michigan, we had our coldest week of April in 25 years, and a new winter storm is likely to bring 2-6 inches of snow on Wednesday. All this wintry weather comes on the heels of the second warmest March in U.S. history. The National Climatic Data Center released statistics showing that March 2007 was 5.6�F (3.1�C) warmer than the 20th century mean of 42.5�F (5.8�C) across the lower 48 states. Only March 1910 was warmer in the 113-year national record. More than 2500 daily record high temperatures were set from the East to the West Coast during the month. On the 13th of March alone more than 250 daily high temperature records were set. The earliest high of 90�F (32�C) occurred in Las Vegas that day and the daily record was broken by 6�F (3.3�C). For the month as a whole more than 200 daily record highs of 90�F or greater occurred in California, Arizona, Texas, Oklahoma, and areas of the Southeast. In contrast, Alaska had its third coldest March ever.


Figure 1. Northern Hemisphere departure of temperature from average for March and the week of April 2-9. Note how the pattern of warmer vs. colder than average temperatures reversed over North America between the two time periods. Images are plotted from the NCAR/NCEP daily reanalysis data, which has interpolation porblems over data-poor areas like the Southern Hemisphere and oceans, so these areas are not plotted. Image credit: NOAA/NCEP.

For the year, the U.S. has had an average January (49th warmest), colder than average February (34th coldest), exceptionally warm March (2nd warmest), and now a very cold April. Climate change science really doesn't have much to say about whether sharp temperature fluctuations like this will become more common in a world undergoing global warming. For now, I'm just attributing the past month's wild swing in temperature to natural variability. The jet stream moved to a completely new pattern between March and early April, reversing where above average and below average temperatures occurred over North America (Figure 1). Where will the jet stream set up for this year's hurricane season, determining the dominant hurricane track? I'll have my first discussion of that in late May, since the jet stream position is generally not predictable more than two weeks in advance.

Swindled?
On Thursday March 8th, the UK TV Channel 4 aired a program titled "The Great Global Warming Swindle". In the words of conservative commentator Thomas Sowell, "Distinguished scientists specializing in climate and climate-related fields talk in plain English and present readily understood graphs showing what a crock the current global warming hysteria is." I've been asked by a number of people to review the movie, but haven't found time to do so. It got yanked from youtube.com for violating copyright laws, but is available from UK TV Channel 4. The scientists at realclimate.org reviewed the movie, and call it a fraud with distorted, misrepresented, and incorrect science.

My next blog will be Thursday.
Jeff Masters