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Warming-Enhanced Texas Drought Is Once in “500 or 1,000 Years … Basically Off the Charts,” Says State Climatologist
Leading experts explain how human-caused warming exacerbates the drought
From October of 2010 through this September 2011, Texas saw its driest year on record, according to the National Oceanic and Atmospheric Administration.
But these historic dry conditions stretch back even further than that.
After examining tree-ring data going back to 1550, researchers at Columbia University found that this year’s drought was only rivaled once in the last 461 years. According to the Palmer Drought Severity Index, a system for measuring wet and dry conditions, the last time Texas experienced a drought this bad was in 1789.
The state’s climatologist, John Nielsen-Gammon, explained the historical significance of the ongoing drought in an interview with CBS:
“This is basically off the charts. Based on past history, you wouldn’t expect to see this happening in maybe 500 or 1,000 years. One more year and we’re already talking about a drought more severe than anything we’ve ever had. And this will become for them, the drought of record.”
The drought, which Nielsen-Gammon says could stretch over a number of years, has devastated cotton crops, livestock, pumpkin crops, and, as the below CBS story points out, Christmas trees. The dry conditions have been exacerbated by a combination of human-caused global warming and La Niña, which pushes unusually cold air from the Pacific Ocean and causes drier-than-average conditions in the Southern U.S.
A number of leading climate experts recently explained the role that they believe human-caused global warming is playing in this epic drought.
As Texas climatologist Katherine Kayhoe put it in an email to Climate Progress, dumping ever-increasing amounts of greenhouse gases into the atmosphere is setting the conditions for turning extreme-weather events into history-setting catastrophes:
We often try to pigeonhole an event, such as a drought, storm, or heatwave into one category: either human or natural, but not both. What we have to realise is that our natural variability is now occurring on top of, and interacting with, background conditions that have already been altered by long-term climate change.
As our atmosphere becomes warmer, it can hold more water vapor. Atmospheric circulation patterns shift, bringing more rain to some places and less to others. For example, when a storm comes, in many cases there is more water available in the atmosphere and rainfall is heavier. When a drought comes, often temperatures are already higher than they would have been 50 years ago and so the effects of the drought are magnified by higher evaporation rates.
The Why Files has comments on the drought from many leading experts:
Gammon: “There is evidence that global warming has had an effect on the drought, primarily by increasing the surface temperature, which increases the drought severity by increasing evaporation and water stress, and by decreasing stream flow and water supply….
… “temperatures have been rising in Tex over past 30 years or so, and they are projected to continue rising at similar rates. We think that the hole is filling, and I am afraid of a rebound effect, where natural variability varies in the opposite direction and the temperature rise would be relatively rapid.”
Richard Alley, professor of geosciences, Earth and Environmental Systems Institute, The Pennsylvania State University
It sure looks like warming, wrote Richard Alley, an expert on climate and ice at Pennsylvania State University, via email. “Our usual scientific response is to say that human burning of fossil fuels has made the events more likely, and they happened,” but conclusive proof is not available. “You as journalists, and the public in general, HATE that. But it’s probably the best answer.
“In a warmer world, we expect more record highs and fewer record lows, more heat waves and fewer cold snaps. That pattern is being observed. Warmer air can ‘hold’ more water (saturation vapor pressure increases with temperature), so if air is warmer when a rainstorm happens, then the rain can be more intense.
“In addition, there is a fairly strong reason to expect that in a warming world the subtropical dry zones (which include the Sahara and the Kalahari, and influence the U.S. Southwest, including parts of Texas) will intensify and expand poleward at least somewhat.
“Suppose you’re playing dice with me, and after you lose, you discover that I stuck some carefully positioned weights inside them. Out in the climate, the dice are now loaded, but not nearly as much as they will be in the future if we keep burning fossil fuels and releasing the CO2 to the air. It is hard to prove that any particular event was extreme because of global warming … but for many events (record heat, drought and flood) it is harder to prove that humans did not influence the outcome, just as it is very hard to prove that my loaded dice didn’t affect the game.”
Kevin Trenberth, distinguished senior scientist, National Center for Atmospheric Research
Is the Texas drought and heat wave due to climate change or natural variation? “There is no doubt a modest component related to climate change, while natural variability plays a major role,” says Kevin Trenberth, a climatologist at the National Center for Atmospheric Research. “Fifteen years ago we suggested that with ENSO [El Nino-Southern Oscillation; periodic variations in water temperatures in the Pacific] the floods and droughts would become more intense.”
… Although the drought is linked to La Nina, it is also exacerbated by climate warming, Trenberth adds. Human climate change adds “about a 1 percent to 2 percent effect every day in terms of more energy. So after a month or two this mounts up and helps dry things out. At that point all the heat goes into raising temperatures. So it mounts up to a point that once again records get broken. The extent of the extremes would not have occurred without human climate change.”
In short, Texas ain’t seen nothing yet, assuming we keep listening to their politicians….
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