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Climate Change Upped Earth's Vegetation, Study Finds

By John Roach
for National Geographic News
June 5, 2003
 
For most of the world's plant life, the effect of the pace of climate change over the past two decades has been productive, according to an analysis of climate and satellite data collected between 1982 and 1999.


The research, reported in the June 6 issue of Science, addresses the question of how global vegetation has responded to changes in precipitation, temperature, and cloud cover patterns. Such climate factors determine how vegetation grows.

Previous studies have looked at vegetation's response to climate change at regional scales, but this is the first study to look at it from a global perspective.

"This is the first global representation of climate changes and how they might influence vegetation," said Ramakrishna Nemani, a climate change researcher at the University of Montana in Missoula who led the study.

According to the analysis, global climate change has eased climatic constraints on plant life around the globe, allowing vegetation to increase 6 percent over the study period.

"For example, in the Amazon cloud cover is a major factor for plant growth and in those areas the cloud cover has declined and solar radiation has increased," said Nemani.

Owing to the added sunshine, photosynthesis has been rampant. The Amazon basin accounts for 42 percent of the global increase in vegetation, according to the study.

Dave Schimel, an atmospheric scientist at the National Center for Atmospheric Research in Boulder, Colorado, was not surprised by the findings and said the research adds new perspective to the field of climate change science.

"Most studies of the effects of climate change have addressed temperature effects, some have also addressed water effects. But some of the most robust observed changes in climate have been in cloudiness and almost no studies have examined trends in solar radiation," he said. "So this is a really interesting new perspective."

Easing Off

The most pronounced effect of increased plant growth as a response to global climate change is in the Amazon basin, where increased sunshine combined with no reduction in rainfall allowed the region to flourish.

In other parts of the world such as Australia, India, and southern Africa, water is the primary driver for vegetation growth. In the last few decades these regions have experienced wetter weather, and thus, increased plant production, according to the research.

For the short-term, at least, this positive effect of climate change is a boon to food supplies required to feed booming populations.

"Take India," said Nemani. "Over the past two decades, especially in the 90s, India had really good monsoon conditions so their crops didn't fail, so in a sense they had a really good supply of food."

This is important for India, where population has gone from approximately 650 million people when Nemani left his native country in 1983 to the more than 1 billion people who live there today.

"Lucky for them the climate has been extremely good for the country, otherwise they would be seeing a lot more food problems," he said.

The problem is that eventually the positive effect of global climate change on vegetation production is likely to reverse. Climate changes go in cycles and Nemani says that "we hit a good patch for the last couple of decades."

In the Amazon, for example, the same amount of rain continues to fall each year even though the cloud cover has changed. What happens if the region starts to dry up? "It will be catastrophic," said Nemani.

This is already happening in Africa, where the equatorial forests are not doing as well as they did in the 1980s. Indeed, according to the study a few parts of world saw their plant production decrease over the two-decade period.

Northern Mexico has become drier and in Siberia the temperature has actually dropped. "It is one of the few places on Earth showing temperature to be cooling, and when you have cooler temperature there, their growing season would be much shorter," said Nemani.

Other Effects

Nemani and his colleagues caution that their study only addresses one aspect of Earth's complex reaction to climate change and that more work is required to understand the entire system.

As a case in point, Nemani said that India had good monsoons even during the El Niño years of the 1990s. According to climate models of the weather phenomenon, India is supposed to have weak monsoons when the weather pattern is in effect.

Climate researchers believe the monsoon is a result of the temperature gradient between the ocean temperature and the land temperature. During El Niño the Pacific Ocean warms up and thus the gradient becomes smaller.

However, over the last two decades Eurasia has warmed up, which apparently maintained the heat gradient required for the monsoon even during El Niño years, according to Nemani. "Things like that are happening all over the Earth," he said.

Another aspect Nemani hopes to investigate is the effect of climate change on biodiversity. Current species distribution in many parts of the world is adjusted to long-term regional climate trends.

"If there are large-scale changes in climate, how would the species compete? Who will be the winners and losers?" he asks. "This has important implications."

NASA satellites launched in 1999 as part of the space agency's Earth Observing System will continue to monitor the Earth to determine if the current patterns in vegetative production continue.
 

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