Grass Loses Ground
On the high plains of the short-grass steppe of northeastern Colorado, where the well-being of livestock and the balance of the regional ecosystem for centuries have depended on the plant life, the grass is dying.
The grass is the victim of nighttime temperatures that for almost three decades have been rising twice as fast as daytime temperatures, researchers at Colorado State University have discovered.
The grass--a species known as blue grama--accounts for 90% of the ground cover in the region and about 40% of the livestock diet. As it gives way to wildflowers and weeds, the cattle have little left on which to forage. The region itself is left more vulnerable to drought because the new plants are not nearly so resistant to extended dry spells or to overgrazing.
“If we see a shift to more of these plants, we may see a disaster when we have a drought,” said Colorado State grasslands ecologist Richard D. Alward.
The fate of the Colorado grassland--and the intricate web of life that it represents--is a crucial example of how global climate change may have subtle effects. Although easily overlooked in the tumult of hurricanes, blizzards, floods and heat waves, these effects could trigger not-so-subtle catastrophes for farmers, ranchers and the animals on which they depend.
Warmer temperatures in recent years have brought spring ever earlier to the Northern Hemisphere--as much as a week sooner than 20 years ago in many countries--according to researchers at the Scripps Institution of Oceanography and UC San Diego.
But until now there has been little direct evidence of the impact on plant life. Researchers had to rely on global temperature averages, seasonal changes in the chemical composition of the atmosphere and elaborate computer models to gauge the effects of climate change.
“This is really the first chance to look at lots of measurements taken on the ground with real plants and tie it into some trend in the climate that we also have good data on,” Alward said.
He led a research team that analyzed 23 years worth of local temperature and vegetation records at a long-term ecological research station on the Pawnee Grassland east of the Front Range near Fort Collins, Colo. Their work was published last week in the journal Science.
The team found that the average daily low temperatures on the grassland had risen 6 degrees Fahrenheit in about 30 years and that each increase of 2 degrees was associated with a 30% drop in the growth of blue grama grass.
Surprisingly, the warmer nights favored the growth of plants that normally thrive in cooler temperatures, Alward said. As the last killing frost of the year comes earlier each spring, the cool-weather plants are getting a head start on the blue grama, which does not start to grow until daytime temperatures have warmed.
“In the short run, climate changes can alter the mix of plant species in land ecosystems such as grasslands,” said ecologist Jerry M. Melillo at the Marine Biological Laboratory in Woods Hole, Mass. “In the long run, climate change has the potential to dramatically alter the geographic distribution of major vegetation types--savannas, forests and tundra.”
Through experiments like these, he said, “scientists are gaining insights into possible future consequences of warming and other aspects of climate change for our life support system, the biosphere.”
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Some scientists believe that the temperature changes are part of the normal up and down of a global climate too complex for anyone to fathom. Many others, though, are certain it is caused in some measure by the burning of fossil fuels and the emission of greenhouse gases such as carbon dioxide.
Concern about the effects of global warming led to the signing of an international agreement in Kyoto, Japan, in December 1997 to reduce emissions of carbon dioxide and other gases thought to threaten the climate.
The Colorado State researchers do not know whether the temperature changes they studied are part of a long-term global warming trend.
The newest insight into climate change comes on the heels of a wave of findings about the world’s weather:
* Global temperatures in 1998 were the warmest in the century that detailed records have been kept, with the worldwide average temperature running a degree Fahrenheit above the average of the past 118 years. It was the 20th year in a row that the globe has been warmer than the long-term average, according to the World Meteorological Organization and NASA’s Goddard Institute for Space Studies.
* The average global temperature last year was 0.34 of a degree Fahrenheit warmer than in 1995, the previous record year. New monthly high-temperature records were set in each of the 18 consecutive months ending in October last year.
* Temperatures in the United States were the warmest in 64 years, since the height of the Dust Bowl era. The U.S. experienced its second-warmest year in 1998, with a mean temperature only one-tenth of a degree Celsius off the record year of 1934. Worldwide, the Canadian Arctic and Alaska were most affected by the heat. Annual temperatures in those regions are running more than 4 degrees Celsius above normal, Environment Canada reported this month.
* The number of “extreme heat stress” days has almost doubled. Researchers who examined 46 years of measurements from 113 U.S. weather stations found a substantial increase in the number of summer days during which the local heat was in the top 15% of temperatures recorded at each station. At the same time, the average number of extended heat waves each year also doubled.
* El Nino may be playing a greater role than expected in shaping the climate of the Northern Hemisphere in part due to the influence of higher temperatures, said researchers at the National Center for Atmospheric Research who studied the behavior of the Pacific Ocean current over the past 6,000 years. Using computer climate models, the scientists determined that the El Nino cycle, which is credited with boosting recent worldwide warming trends, has been twice as powerful in recent years as it was in 4000 BC.
The El Nino cycle continues to grow in strength because it is serving to dissipate the heat from rising global temperatures, the researchers said.
A new computer model of global climate developed at the atmospheric research center predicts that Earth’s mean surface temperature should continue to rise at the rate of about one-third degree Fahrenheit per decade for the next 40 years.
Even so, several experts expect that the world actually may be cooler in the coming year, as the warming effects of last year’s powerful El Nino wear off and the cooler La Nina portion of the Pacific Ocean cycle asserts itself.
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Warm on the Range
For almost three decades, nights in eastern Colorado have been getting warmer twice as fast as days because of rising temperatures that are lengthening the growing season throughout the Northern Hemisphere, new research shows.
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The weather was anything but normal in 1998. This NASA map shows where temperatures were warmer or colder than normal around the world. The map shades from dark red--warmer than normal--to dark blue--cooler than normal.
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Global surface temperatures in 1998 were the warmest on record. This chart shows how much temperatures were above or below normal, in degrees Celsius. There has been a steady warming trend since 1880.
EL NINO
Nov. 18, 1997
This Topex/Poseidon satellite image of the Pacific shows that 14 months ago the El Nino current--area in white--was gathering strength. El Nino helped boost record warm temperatures.
LA NINA
Dec. 4, 1998
A year later, El Nino has ebbed and its counterpart, a cold water current called La Nina--area in purple--is now in ascendance, bringing cooler weather worldwide.
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SOURCES: NASA Goddard Institute for Space Studies, Jet Propulsion Laboratory, Colorado State University, National Science Foundation
