Contact: Sharon Keeler, UNH News Bureau, 603-862-1566
DURHAM, N.H. -- Unusually warm temperatures can wreak havoc on the world's climate, but these warming periods also have an upside that may help researchers better understand global climate change.
In a new study published in "Science" magazine, University of New Hampshire earth scientist Rob Braswell and his colleagues describe how a warm anomaly may help temporarily brake the ongoing rise in atmospheric carbon dioxide attributed to human activity. The reason: two years after a warming, increased global plant growth seems to soak up excess carbon dioxide.
"Our research offers insight into how ecosystems moderate the effects of temperature variability on atmospheric CO2," says Braswell, research scientist in the university's Complex Systems Research Center. "The results move us forward in our understanding of the mechanisms that explain the earth's responses to climate change."
Atmospheric carbon dioxide concentrations have increased steadily over the past 20 years, continuing a trend more than a century old that is attributed largely to the rising consumption of fossil fuels and large-scale destruction of forests.
Within this period, however, there are shorter term fluctuations. These fluctuations are what what Braswell and fellow researchers, Berrien Moore III, director of UNH's Institute for the Study of Earth Oceans and Space, Ernst Linder, UNH professor of mathematics, and David Schimel, of the National Center for Atmospheric Research, focused their study on.
Using powerful satellite based techniques, the scientists analyzed carbon dioxide levels, global temperatures and plant growth for the years 1981 through 1990, a period that included a number of unusually warm spells. What they found was that the rate of increase of atmospheric carbon dioxide levels slowed significantly about two years after each of the warm periods. Global vegetation growth, as measured by light reflected from photosynthetically active leaves, also accelerated, a sign that the plants were taking in the excess carbon dioxide.
Conversely, the researchers found that after a cool anomaly, plants absorbed lower than average amounts of carbon dioxide.
The two year lag, says Braswell, indicates that the plants aren't simply responding directly to temperature. Other ecosystem processes -- the interaction between soil and plants -- act as a middleman between warming and plant growth.
"We hypothesize that the increased plant growth is associated with processes in the soil involved with the availability of nutrients such as nitrogen," he says. "It appears that warming increases the activity of microbes that make nutrients available in the soil. This makes conditions more favorable for growth, and the act of growing requires more CO2."
Braswell says the research results provide evidence that the world's ecosystems, climate, and carbon levels are inextricably linked when it comes to analyzing global climate change.
"In analyzing global change, predicting terrestrial carbon exchange is crucial," he says. "If the earth's biosystems increase their carbon storage, as they do after a warm spell, than atmospheric carbon dioxide emitted by human activity will be offset. If terrestrial carbon is expelled at an increased rate into the atmosphere, or the absorption rate by plants decreases, than climate change could be exacerbated."
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