THE HEAT IS ON
Biologists probe effects of global climate change.
Written by John Davis
David Tissue studies climate changes at Big Bend National Park.
Biologists probe effects of global climate change.
How will an average temperature rise of as little as 2 degrees Fahrenheit affect ecosystems around the globe? David Tissue, an associate biology professor at Texas Tech, is trying to find out. It’s a fair question since modeling predicts earth’s temperatures could rise 2–10 degrees Fahrenheit by the end of this century.
Most scientists agree that the earth is getting hotter, and NASA’s Goddard Institute for Space Studies found that 2005 had the highest global temperatures in more than a century. Other recent years are also among the hottest.
Tissue says climate changes, caused largely by an increase in carbon dioxide in the atmosphere, can cause massive changes in ecosystems as variable as rain forests and deserts. Though carbon dioxide levels have played a role in earth’s temperature in the past, cores of ice studied in Antarctica show it remained constant for about a thousand years.
Then the Industrial Revolution of the 19th century came along. Tissue says the burning of fossil fuels has been the main culprit in putting about a third more carbon dioxide into the air than existed before. Deforestation for agriculture has also played a role by removing plant life that scrubs CO2 from the air.
Global climate change starts with increased greenhouse gases. This increase traps more heat in the atmosphere. Air and water temperatures go higher, changing air and ocean current circulation patterns. Changes such as more or less rain begin to occur.
Studying the planet
An ecology class at McGill University in Montreal, Quebec, led Tissue as an undergrad to pursue questions about the impact of changes in global climate on our environment.
In the 1980s he studied how elevated atmospheric CO2 and warmer temperatures would impact native grasses in Alaska’s arctic tundra.
“We spent two weeks walking around the tundra north of the Brooks Range selecting our research site near Toolik Lake,” Tissue says. “Then we went back to San Diego and spent a year designing and building greenhouses that we used to elevate atmospheric CO2 and temperature in the tundra the following summer. We warmed the tundra by four degrees Celsius and doubled the CO2 concentration to determine the impact of our future predicted environment on the dominant plant—tussock grass—in the arctic ecosystem. “
At first the grasses increased photosynthesis with warmer temperatures and more carbon dioxide. But in three weeks they had used up the nutrients in the soil, returned to their former rate of photosynthesis and stopped their rapid growth.
Tissue says this was the first study conducted in a natural ecosystem to demonstrate that plant response to elevated CO2 and temperature may not be as positive as first predicted.
Now Tissue and John Zak, chairman of biological sciences at Tech, are studying how climate change will impact the plant and microbial communities of Big Bend National Park. This work in the Chihuahuan Desert is part of a larger study also involving the universities of Arizona, Nevada-Las Vegas and California-Santa Cruz. Scientists at all four institutions are looking at how plants in North American deserts are affected by more rainfall.
“It’s important to figure out how arid lands will respond to changes in water availability,” Tissue says. “They represent about 25 percent of the world’s land area and are generally very sensitive to changes in the timing and amount of rainfall that they receive.”
The Big Bend project grew out of long-term monitoring Zak initiated there as part of a network of sites that were funded by the United States Geological Survey. The goal was to examine impacts of climate change and pollution impacts on several other national parks.
“If park managers are to make ecologically relevant decisions, they need to know what is happening to the integrity of the landscape,” Zak says.
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