Volume 78/Number 2
Spring 1998

Tennessee Alumnus
Home Page

UT Home Page

How's the Weather?

Weather disasters pound our planet even as we continue to mistreat the environment. Are the two situations related?

By Yvonne Loveday

 

For years we've been warned of impending ecological disaster if we didn't change our gas-guzzling, aerosol can-toting ways.

Last December we were re-reminded when the U.S. pledged-as part of a historic international pact-to reduce harmful emissions five percent to help curb global warming.

While we've pondered the problems of ozone depletion and global warming during the last decade, we've been buffeted by no fewer than 25 weather-related disasters, including ice storms in the Northeast; severe flooding in the Dakotas and Minnesota; blizzards in the Mid-Atlantic and Northeast, and Hurricanes Andrew and Hugo. And don't forget El Niņo, which came our way late last year-the largest ever weather pattern of its type.

Is our mistreatment of the environment connected to these weather disasters? Are we on the brink of a climate crisis? Dr. Ken Orvis, UTK assistant professor of geography, gives an expert opinion.

 

The Big Picture

Earth's climate system is incredibly complex. Trying to understand it, Orvis says, is like a flea who lives on a very large dog trying to comprehend all the canine bodily functions.

Research shows the last century-in fact the last five centuries-has been one of the most stable weather periods in the last 10,000 years.

"The last 100 years have been benign, predictable, pleasant," Orvis says. "So we have developed models that can tell us about this very nicely behaved period of time, but that's all that we have to go on. Looking back, we do know that there have been sudden changes in the way the Earth's climate system behaves."

Scientists say that 75 million years ago the Earth's average temperature was about 10 Fahrenheit degrees higher than it is today. Cold periods have come and gone as well. At the peak of the last ice advance 20,000 years ago, the global average temperature was about nine Fahrenheit degrees lower than it is today.

"It's clear that the climate would be changing along about now in all likelihood with or without global warming and other anthropogenic influences."

But global warming and influences like ozone depletion and El Niņo weather patterns do exist. While we may indeed be at the brink of a global climate change, dangerous levels of manmade pollutants are also affecting the thermal balance of the atmosphere.

"The core issue is the magnitude of risk," Orvis says. "The amount of risk in what we could do is large enough that we should want to change our behavior until we know for sure what's going on."

 

Global Warming

"Global warming is a change in the entire average temperature of the atmosphere and oceans worldwide caused by excess greenhouse gases produced by humans," Orvis says.

Carbon dioxide and other gases generated in human agriculture and industry are trapping the sun's heat, causing the global temperature to rise. And while no one knows for sure what the consequences will be, the worst case scenarios envisioned by scientists include dangerously rising seas, more powerful storms, and altered weather patterns.

Human activity, mostly in the consumption of fossil fuels, is now generating 24 billion tons of carbon dioxide a year.

"America, all by itself, puts out somewhere between 25 to 34 percent of all emissions in the world. Every gallon of gas we burn produces 20 pounds of carbon dioxide," Orvis says.

Without steps to curb these greenhouse gas emissions, the average global temperature is expected to rise from two to nine Fahrenheit degrees by 2100, says the Center for Global Change Science at the Massachusetts Institute of Technology.

How can such a small rise in temperature affect our climate on such a monumental scale?

"Picture a pot of soup barely simmering on the stove," Orvis says. "Now turn it up just a little bit."

The additional heat, though small, will cause the soup to churn faster.

"That's the risk of global warming," he says. "It won't change the soup's temperature very much. It might not even boil, but it will change the dynamics of how the soup is circulating. Those patterns of movement on top can change a whole lot even though the temperature doesn't change very much. The Earth's climate acts the same way."

 

Ozone Depletion

Human activities also release other greenhouse gases, such as methane and chlorofluorocarbons (CFCs). These intensify the heat-trapping prop-erties of the atmosphere as a whole.

CFCs also rise into the upper layer of the atmosphere, or stratosphere, where they destroy the protective layer of ozone, a gas which forms a shield against ultraviolet rays that can harm many forms of life, says Orvis.

In our lower atmosphere, or troposphere, manmade CFCs contribute to pollution and global warming, but in the stratosphere, they react with high-energy photons, releasing chlorine, which attacks the protective ozone layer. One CFC-spawned chlorine atom can catalyze the destruction of as many as 100,000 ozone molecules.

About 20 million tons of CFCs have been released worldwide since the mid-1970s, according to the World Resources Institute, an environmental policy research center in Washington, DC.

As ozone is lost, the amount of biologically harmful UV-B radiation will increase, causing skin cancer rates to rise. Other health effects will likely include an increase in cataracts and suppression of the immune system. Crop diseases would increase as the ultraviolet radiation breaks down the natural resistance of plants. Global climate change could be intensified.

"By now, everywhere-even here in Tennessee-the amount of ultraviolet radiation is significantly higher-about 10 percent higher than in 1960," Orvis says.

 

El Niņo

Some people believe that global change has contributed to the intense and more-frequent-than-usual El Niņo weather patterns that have occurred since the mid-1970s. On this, scientific opinion is divided.

El Niņo occurs when the easterly winds die down, allowing warmer waters in the western Pacific to drift eastward towards the Americas. This shift in warm Pacific water upsets the atmosphere's energy balance. The warm, ocean water supplies both moisture and energy for huge thunderstorms which influence jet stream winds. These changes, in turn, move storms on unusual paths, upsetting normal patterns of wet and dry weather.

"When people ask if the weather is caused by El Niņo this year, the answer is yes. Even if our weather is more normal than weather ever is, it's still caused by El Niņo. Without El Niņo it would certainly be different. It's another piece of the picture," Orvis says.

 

Putting It All Together

If we are on the brink of a natural global climate change, the addition of manmade pollutants in our atmosphere can only add fuel to increasingly extreme weather patterns.

Greenhouse gases increase our temperatures, making weather more "energetic," says Orvis. At the same time the ozone layer is cooling and thinning.

"Because the amount of energy in a thunderstorm depends on how much room it has to roam in and how high the convection cells can go, you will be getting even more energetic storms," he says.

Warmer temperatures contribute to the melting of the polar ice caps, increasing sea levels. While this may not directly affect El Niņo weather patterns, it is another part of the equation.

However, the National Center for Atmospheric Research says El Niņos are likely to become more frequent and more intense as Earth grows warmer.

 

What You Can Do

Orvis says reducing carbon dioxide emissions should be our biggest concern, and he suggests two simple things we can do: plant trees and use "clean" technologies-those that generate little or no emissions-as they are developed.

"A tree will pull carbon dioxide out of the atmosphere for 30 to 100 years. It's not a permanent solution, but it will buy us time to make bigger changes."

Trees will also shade buildings from the sun. The cooler the building, the less need for air conditioners, the less electricity consumed.

"Think about almost everything you do in terms of energy conservation," Orvis says. "We've got to get into that habit."

If faced with a choice between a small fuel-efficient car or a 4X4 with a huge engine, buy the smaller car, he says. Buy "clean" cars, refrigerators, and air conditioners as they become available.

Almost everyone involved in the climate debate agrees that deep reductions in carbon dioxide emissions cannot be made without the use of green technologies.

"Science is moving so rapidly," Orvis says. "So many fundamental things are being learned, but there's a tremendously long way to go."