Urban Ecology

Making Changes

by Diane Boudreau

At one time, people thought that only gods or magic could change the weather. Now we know that people can change it in many ways. The biggest example is global warming.

Scientists describe global warming as a rise in the Earth’s average temperature. They think that one cause might be the addition of extra carbon dioxide in the atmosphere. The carbon dioxide acts like a blanket. It holds the sun’s heat close to the surface. Many human activities release carbon dioxide into the air. All of these activities contribute to global warming.

Global warming is a very slow change that affects the climate all around the planet. “Climate” is the average of all the weather conditions that occur in an area. It includes temperature, humidity, rain and snow, and weather events such as El Niño or heat waves. Climate change can be caused by large, global factors like global warming, or by smaller, regional factors.

“Climate change occurs globally and locally,” says weather expert Tony Brazel. Brazel is a climatologist and professor of geography at Arizona State University. “Phoenix is affected by global climate patterns. But there are other climate patterns that happen only in this area.”

People have made changes to the Phoenix area environment. Brazel says that these changes have also changed the local climate.

“We have created a kind of artificial climate. We import water that wasn’t here before, for example. That affects humidity,” he explains.

Average temperatures have climbed higher in Phoenix. Brazel says the rise in temperature due to the “heat island” effect. The city actually becomes warmer than the surrounding countryside. The result is a little “island” of heat.

“In downtown Phoenix the minimum average temperature in summer has increased about 10 degrees Fahrenheit. This is one of the largest changes attributed to urban growth anywhere,” Brazel says. “In the last 50 years or so, there’s been an increase in the minimum temperature. It does not get as cold at night in Phoenix as it used to.”

So far, scientists haven’t found any major changes in the levels of precipitation (rain and snow) in the Phoenix area. Humidity levels also have stayed about the same.

“We take readings at Sky Harbor Airport. Those readings have shown that there’s not much overall change in moisture over time,” says Brazel. However, he says changes in humidity are hard to measure. They may be happening on a smaller scale.

“When the sky is clear, you can drive through town and hit moist areas and dry areas. It’s like a patchwork quilt,” he says. Golf courses and lawns create little pockets of humidity, while big shopping centers are dryer than average.

“It’s hard to generalize that to what’s happened over time.”

Phoenix has never had much wind. Brazel says that some research results indicate that the increased heat of the city could be increasing local wind.

All of these changes have effects on the environment as a whole. For example, higher temperatures can make ozone problems worse because ozone forms in hot weather.

Studying these connections is what urban ecology is all about, says Brazel.

“We know that an urban climate exists,” he adds. “Scientists want to know how this climate affects things in the ecosystem. Is it affecting the comfort of people? Does it affect energy consumption? Water use? All these questions are going to be linked with climate.”