Analysis of Winter’s Wacky Weather Remains Up in the Air

North America’s spine, the Rocky Mountains, is saddled with a snowpack nearly 200% of normal, portending flooding and mudslides through much of the West when the white stuff melts.

Since December, Yellowstone National Park has been encased in sheets of ice, forcing unprecedented numbers of hungry bison to migrate beyond their federally protected domain in search of forage, and leading hundreds to be shot or slaughtered.

Now, a year after a man-made flood repaired Grand Canyon sandbars and beaches to create spawning grounds for fish, the prospective thaw of the Rockies’ heavy snowpack is forcing operators of Glen Canyon Dam to release millions of gallons of water that may wipe out those improvements.

Coastal Oregon and Washington state are having their wettest and snowiest winter on record. The same weather systems have unleashed flooding that has ravaged Northern California.

So what gives?

Kevin Trenberth, a scientist at the National Center for Atmospheric Research at Boulder, Colo.--the capital of weather analysis in the United States--has a few answers.

One, it’s winter.

Two, Trenberth sees a link between global warming and extreme climate changes that seem to be “enhancing storminess” across the nation and around the world.

Essentially, he says, increases in greenhouse gases such as methane, nitrous oxide and carbon dioxide--all created by human activities--are boosting global temperatures. Carbon dioxide levels have increased about 30% in the past 150 years, mainly as the result of burning fossil fuels in factories and vehicles, he said.

But about three-fourths of the Earth’s surface heating is going into evaporating moisture, which Trenberth calls “the great air conditioner of the planet.”

“If you increase evaporation, you also increase the moisture content in the atmosphere, which increases precipitation,” Trenberth said. “That, I believe, may be related to the wacky weather going on.

“If you have a precipitating system such as a cloud or a snowstorm, the extra moisture in the atmosphere gets caught up in it and produces heavier rainfall and snowfall than would otherwise occur,” he said.

This winter, he theorized, that may mean larger-than-normal amounts of moisture from the tropical Pacific and the Gulf of Mexico being swept aloft and dumped as rain and snow on Washington, Oregon and Southern California and across Nevada, Utah and much of the Rocky Mountain West.

It also may mean that fluctuations in the jet stream, storm tracks and drought cycles caused by El Nino warm episodes and La Nina cold episodes in the tropical Pacific Ocean are being magnified by climbing global temperatures, Trenberth and other climatologists said.

To be sure, not everyone agrees that the greenhouse effect will produce climatological changes large enough to worry about.

“I don’t disagree with the idea that global warming will tend to make the hydrological cycle more vigorous,” said John Wallace, a professor of atmospheric sciences at the University of Washington at Seattle. “My problem is with how strong the effects are at this point in time.

“The amount of warming we’ve had so far,” he said, “is comparable to the change in climate if one moved from northern to southern suburbs in a major metropolitan area.”

Trenberth, however, sides with those who believe that the rate of these changes is larger than at any other time during the past 10,000 years.

So does Tom Karl, senior scientist at the National Climate Data Center in Asheville, N.C.

“About 2% more precipitation per year across the United States now falls in these extreme events compared to earlier in the century,” Karl said.

Flooding along the Mississippi River in 1993 may have been an example of that. With similar trends unfolding in Australia, South Africa, Mexico and Canada, Karl said, “We may be witnessing the first discernible impact of human activity on global weather.”