U.N. sees drought in state's future
Climate: ‘Either we have a clear signal ... or everybody (is) wrong'
Report predicts last 2 years were rehearsal for global warming.
U.N. sees drought in state's future

By Josh Rabe

Published: April 29, 2007

Global warming will make droughts like the one Oklahoma recently escaped and even mega-droughts like the Dust Bowl of the 1930s more common in the future, according to a climate study released earlier this month.

The study indicated current warming trends will permanently change the climate of the American Southwest. That includes Oklahoma, although to a lesser extent, said David Karoly, a meteorology professor at the University of Oklahoma.

Although most climate scientists can't prove recent drought conditions in Oklahoma and a current drought in the southwest are linked to global warming, they paint a good picture of the future as the earth heats up, Karoly said.

"It is interesting that the first part of this decade in the last five years or so have seen relatively dry conditions in much of the southwestern United States, similar to the sort of things that are being talked about in the future simulations. But those (future simulations) showed more prolonged drought conditions,” Karoly said.

Karoly is a member of the United Nations-sponsored Intergovernmental Panel on Climate Change, which analyzed the results of the study, although he did not participate in the most recent report.

The study used 19 independent computer simulations to project what will happen to the earth's climate as greenhouse gases build up in the atmosphere and the planet heats up. All but one simulation agreed that the already-arid areas of the southwest will become much hotter and drier by the end of the century.

"When the models are all agreeing it can tell you one of two things: either we have a really clear signal of what is right or everybody had the wrong idea about what is going on in the first place,” said Mark Shafer, a climatologist for the state climatological survey.

The warming effect will be more pronounced in areas farther west, including parts of Arizona and southern California, which are already struggling with drought. Oklahoma will clearly feel the effect, though, Karoly said.

The panel is expected to release a report Friday focusing on how the effects of warming can be mitigated.

Computer simulations showed the current warming trend and continued buildup of greenhouse gases will alter the planet's prevailing wind and rainfall patterns, specifically in the southwestern United States.

The way global weather patterns work now, hot air rises from equatorial tropics until it is blocked by the upper atmosphere and spreads to 10 degrees to 30 degrees latitude before cooling and falling back down. The computer models show the area covered by the hot air mass, which suppresses rainfall, will grow larger as the planet heats up.

Essentially, the arid climates of Mexico and Central America would be migrating northward, Shafer said.

As the earth warms, what meteorologists call the "storm track” will shift toward the north, leaving the southwest drier than it is now, Karoly said.

Although the future painted by the study may be bleak, it isn't absolutely certain.

"There is greater confidence in the temperature change in the future climate than there is in the change in rainfall patterns, but this is an interesting result because it does show consistent changes in rainfall, coupled with warmer temperatures,” Karoly said.

Shafer said it's possible warmer temperatures could lead to more rainfall.

Current methods of predicting climate change in the future are only specific enough to target general trends over a broad area, he said.

"We know there is going to be a temperature change, but there are a number of predictions of where precipitation occurs,” Shafer said.

Maybe, Shafer said. There have been a few telltale signs that the climate is changing in recent years, but it would be difficult to say whether any of those are linked to global climate change or are just local anomalies.

This spring, for example, warm weather arrived earlier than expected in March and vegetation began to bloom earlier than normal. However, a late freeze in April damaged many of the plants that had sprung to life early.

"Overall, spring has been starting earlier in the past couple of decades,” Shafer said. "That extends the growing season, but it does also expose us to a higher risk of a late freeze. The vegetation essentially thought it was two or three weeks later than it was. The date of the freeze wasn't the problem, it was the warm conditions before it.”

In general, Oklahoma has warmed up in recent years, but it is difficult to say whether that is a result of global warming or just happened by accident. "I wouldn't say there is a trend we would see yet,” Shafer said. "There does seem to be a shift. Warmer in spring, cooler in summer, but it balances out over the last couple of decades.” The state also experienced one of its hottest summers last year and only emerged from a two-year drought in the last month. Although scientists can't say with any certainty whether that drought was caused by global climate change, it provided Oklahomans with a good lesson in it, he said.