controlled burn

Controlled burn in the Davis Mountains to reduce fuel for wildfires

Once again, a spate of weather extremes and disasters is prompting news coverage of the possible connections to climate change.

Is manmade global warming a factor? Can anyone really say, one way or the other?

This time around, the events prompting such questions have prominently included Texas’ widespread drought and thousands of wildfires and the wave of killer tornadoes that swept across the Southeast.

We’re decidedly not in the prediction business here at TCN Journal, but we’ll make a rare exception to that rule: This won’t be the last time that weather extremes trigger speculative discussion about links to a warming climate.

In the case of the current Texas conditions, not all statements in the news media have been related to human influences on the atmospheric system, of course.

Last week, Gov. Rick Perry, famously skeptical about manmade global warming and fiercely antagonistic to regulatory action to attack it, got a good deal of attention for his official proclamation of three “days of prayer for rain in Texas.”

Explaining his call for Texans to ask for divine intervention, Perry cited the “exceptional drought, with some parts of the state receiving no significant rainfall for almost three months, matching rainfall deficit records dating back to the 1930s,” plus the “higher than normal temperatures, low precipitation and low relative humidity [that] has caused an extreme fire danger.”

For a number of reporters, a go-to source for scientific commentary on that situation was the state climatologist, John Nielsen-Gammon, who serves on the faculty of the Department of Atmospheric Sciences at Texas A&M University and does not share Perry’s skepticism about the conclusion by the vast majority of climate scientists that human beings are heating and otherwise changing the climate.

Nielsen-Gammon told the New York Times that Texas’ increasing rainfall since 1895 does not jibe with computer models’ projections of declining precipitation in the state as the global climate experiences an average warming.

The reason for this difference is unclear, he said, but it could be attributable to factors like variations of sea-surface temperature patterns, modeling flaws or changes in aerosols or land use.

“Certainly global warming has contributed to the rate at which the ground has dried out because of the warm temperatures,” Dr. Nielsen-Gammon said. But, he added, “the magnitude of the dryness is well beyond what global warming would be able to do so far.”

He also spoke to the Dallas Morning News [the link leads to another newspaper’s web-posting of the McClatchy-Tribune news service’s version of the article]:

Scientists say the immediate cause is a La Nina, a recurring, months-long pattern that blocks Texas’s normal rains.

But are the drought and fires also linked to climate change?

Climate scientists say that question, though common whenever extreme weather arrives, is both unanswerable and misdirected.

“By now, most people get that you can’t attribute any single weather event on global warming,” said John Nielsen-Gammon, the Texas state climatologist and a professor at Texas A&M University.

[… Much of the state’s increased precipitation] has come from more-frequent extreme rainfall events rather than a general increase in normal rain.

Warmer air holds more water, contributing to extreme rainfall. However, higher temperatures also dry out plants and soil more quickly, worsening droughts — perhaps including the ongoing one, Nielsen-Gammon said.

Future rain and drought patterns aren’t certain, he said.

“But some things are clear: Temperatures have been going up, and models all agree that the temperature rise will continue unless we get some massive volcanic eruptions or the sun suddenly becomes much dimmer,” he said.

He told the Houston Chronicle that “climate change has probably had a couple of secondary effects” on the current drought:

“For one thing, some of the burned areas, especially the one in northern Mexico, received some excessive rainfall during the summer. Global warming probably produced a slight enhancement of the rainfall, leading to a little extra plant growth. Also, the warm temperatures during the past couple of months are probably a degree or two warmer than they would have been without the rise in global temperatures, thereby increasing the dryness.

“On the other hand, warm global temperatures would be expected to have made the cold weather last winter a little less severe, so there probably wasn’t as much plant die-off over the winter as there would have been without climate change, so this factor would have worked to make the fires less severe.”

And what about the rash of tornadoes that brought death and destruction to several states this week? The New York Times reported:

“There’s a lot we understand about tornadoes,” [Kevin Trenberth, senior scientist at the National Center for Atmospheric Research in Colorado] said. “They’re tied to thunderstorms, and also require something that will cause the rotation to occur, a wind shear.”

And all of these ingredients have been in abundant supply in the areas of the country that have been hit hardest this month than in any April since current counting methods began. Nevertheless, scientists can only guess when and where tornadoes will actually strike.

When technology can predict oncoming storm tracks and conditions with greater certainty than ever, and scientists assert with growing unanimity a human impact on climate, what is a natural act of God and what is more correctly the province of humans themselves? Where is the place of psychic shelter in an age when the lines between fate and human action are blurred?

The prevalence of hurricanes, droughts and floods has been linked in many climate models to the impact of a warming planet. Such a connection is more tentative when it comes to twisters.

“Tornadoes are tougher,” said Jeff Masters, director of meteorology at Weather Underground, an Internet-based weather service.

Many climate models, for example, predict a weakening upper atmosphere jet stream over time on a warming planet, Dr. Masters said, which would presumably create less energy for tornado formation. But some of those same models also suggest wetter conditions in tornado country, which is the other key ingredient in storm formation.

At the same time, more people are also living in areas where tornadoes strike, across the broad band called Tornado Alley in the nation’s midsection as well as in the South, so the number of observed and recorded tornadoes has steadily gone up.

The Toronto Star also was among those seeking scientists’ insights into the question of a link between climate change and  tornadoes:

While a raft of climate science points to a stormier future involving more frequent and possibly more severe hurricanes, researchers have yet to factor tornadoes into climate-change predictions with any certainty.

Theories abound, however, including a 2009 University of Georgia study that suggested climate change could in fact bring about fewer tornadoes in the southeastern United States, which sustained the worst of the Tuesday’s devastation.

But Purdue University climatologist Dev Niyogi, one of the co-authors of the Georgia study, cast doubt on even those findings in an interview Wednesday. Niyogi, like many climate experts, described with awe the sheer rarity of complex conditions that made Tuesday’s storm formations unlike anything the region has seen since the 1970s.

“The simple answer is we don’t really know whether climate change is going to cause more tornadoes. The jury is still out,” Niyogi told the Toronto Star.

“But the good news is the science is maturing. And while the first order of business is to restore the lives of these communities, from the science end, it is highly likely that the data are going to help us understand the cause of these major outbreaks.”

– Bill Dawson

Image credit: Frank Cianciolo/University of Texas McDonald Observatory