Is the Weather Stuck on Extreme?

By Barb Adams

2012 is starting out with a fury, with tornado outbreaks reported in January, February, and March.  And now the recent outbreak in Dallas-Fort Worth in April.  This article was written in response to some thoughts about extreme weather events and climate shifting and change.

Extreme weather events, from record-breaking tornado outbreaks to record-breaking temperatures, drought, and snowfalls, are forcing the climate change issue—but is the warming weather actually causing an increase in numbers and strength of storms?

On Tuesday, a dozen tornadoes swept through the Dallas-Fort Worth metropolitan area causing extensive damage and injuries.  Fortunately, no fatalities were reported.  Although it is not uncommon for the Dallas-Fort Worth area to be hit by tornadoes, “having two major systems strike a single metropolitan area is highly unusual,” said meteorologist Jesse Moore.  The Dallas-Fort Worth outbreak came on the heels of several other deadly tornado outbreaks that occurred earlier this year, and followed an exceptionally deadly and destructive year for tornadoes in 2011 (552 deaths, which ranks second in number of deaths in a single year in U.S. history).

Tornadoes can occur at any time of the year in the U.S., with “tornado season” officially beginning in March and peaking in May and June across the Central U.S.  This year, like last year, tornado season began early in January, when a significant outbreak occurred across the southern states. There was another outbreak in February (Leap Day Outbreak), followed by one of the largest outbreaks ever recorded for early March, with 160 tornadoes.  Thus far in 2012, 57 people have been killed as a result of these storms.

Records indicate that we’re breaking more heat records than cold records.  The winter of 2011-2012 was the fourth warmest on record, and March 2012 was the hottest ever for much of the nation.  More than 6,000 high-temperature records were broken and, according to Accuweather.com, “…cities in more than 25 states, as well as Washington, D.C., broke records for average daily temperatures last month, including Chicago, Oklahoma City, Des Moines, Milwaukee, Indianapolis, and Detroit.”

While most of the nation enjoyed the benefits of the warmer, drier winter, Anchorage, Alaska, endured a brutal winter (as did much of Europe and Asia).  Extremes swing both ways.  As Dr. Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colorado, points out, “Extremes are always expected to happen as the climate record gets longer, but certain extremes related to heating are becoming more evident.  For example in the United States, extremes of high temperatures have been occurring at a rate of twice those of cold extremes, and this has accelerated considerably since June 2010…Texas, Oklahoma, New Mexico and Louisiana all suffered their hottest June-July-August (JJA) 2011 since 1895…(and) Texas also experienced the driest JJA on record.”

And Texas isn’t alone. Colorado is experiencing an unusual drought as well, with early-season wildfires already claiming several lives.  According to The Denver Post, “98 percent of the state is experiencing varying levels of drought;” and Wendy Ryan, a Research Associate at the Colorado Climate Center, noted that “In Fort Collins, we had the hottest and driest March on record … This is the first time we’ve ever had only a trace of precipitation for March.  No years have had zero.”

Does a warming climate mean more severe weather, and are we already seeing the effects of this warming?  Meghan Evans, a meteorologist with AccuWeather.com believes that “There is no strong evidence to support severe weather becoming stronger, more frequent or more widespread during the past 50 years in the United States as a result of climate change.”

So why does it seem that tornado outbreaks and extreme weather events, including drought, are becoming more common across the country and around the world?  According to Research Meteorologist Dr. Harold Brooks of NOAA’s National Severe Storms Lab in Norman, Oklahoma, “The big reason why we think that severe weather has gotten worse is our ability to communicate information about it…we are more aware and able to communicate that information about events so much better than we used to be able to that it makes us think severe weather has increased.”

But with records indicating a trend of warming temperatures, what might the impact be of future climate change on weather-related events?  “As the planet warms, the moisture content of the atmosphere will also increase, and that’s the basic fuel that drives thunderstorms,” says Brooks.  “It’s where the storms get their energy from… as we warm the planet that will increase the energy available for producing storms.  The other primary ingredient, the shear that organizes the storm, is likely going to decrease.  We may see a shift toward non-tornadic wind storms in the future, but that’s still a preliminary result.”

Meghan Evans concurs.  “Straight-line winds may increase since high wind shear is not as much of an influence, while the frequency and strength of tornadoes may not change very much.  It is difficult to conclude confidently whether the regions that get the most severe weather and tornadoes will shift as the climate warms.”

“Our primary understanding of what will happen in the future with severe weather is actually based on our current understanding…Then we look in the future from climate models and from basic physical understanding of how the atmosphere works to understand how those basic environments will change,” Brooks added.

Better understanding of climate cycles will come with our increased ability to detect and report weather-related events.  In the meantime, however, society has to deal with all the extremes.  As Stanford University Climate Scientist Chris Field states, “We mostly experience weather and climate through the extreme.”  Mark Twain may have said it best, though, when he quipped “Climate is what we expect, weather is what we get.”

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