September 6, 2001

LOS ANGELES – As Earth gets warmer, it's getting greener, researchers studying 20 years of satellite data have found.

The team from Boston University and NASA's Goddard Space Flight Center found that vegetation is growing more vigorously over much of the Northern Hemisphere. That may prove to be too much of a good thing, said Ranga Myneni, one of the study's authors.

"What's good for the plants is not necessarily good for the planet," said Myneni, an associate professor of geography at Boston University. "(Climate change) means accepting the fact that it's getting warmer ... and having increasingly frequent events like downpours and hurricanes. All of those have serious consequences."

The study, to be published Sept. 16 in the Journal of Geophysical Research-Atmospheres, found that regional increases in greenness coincided closely with increases in temperature. Increases in vegetation were more common over Europe and northern Asia, which have seen more warming trends than North America.

Increasing human production of carbon dioxide and other "greenhouse gases" is widely blamed for rising global temperatures. In the northern latitudes, which the study focused on, temperatures have risen about 0.8 of a degree Celsius since the 1970s.

Other research has found that flora and fauna ranging from shrubbery in Alaska to butterflies in Europe are stretching their territories northward as the mercury rises.

The findings "confirm what I think a lot of scientists already suspected," said Michael E. Mann, a professor of environmental science at the University of Virginia who researches climate change but was not involved in the study. He added that the study is important because it uses satellite data to bolster evidence for human-caused climate change.

The study analyzed data from weather satellites from 1981 to 1999 for Europe, Canada and most of the United States and Asia.

In a wide area from central Europe to Siberia, between 40 degrees and 70 degrees north latitude, they found that more than 60 percent of the vegetated area has been growing more vigorously over the last two decades. In addition, the growing season in Eurasia grew by about 18 days, the researchers found.

The changes were less pronounced in North America, which has actually seen average temperatures fall in some eastern areas. The Western Hemisphere saw greener landscapes only in southeastern forests and the grasslands of the upper Midwest.

Parts of Alaska, northern Canada and southeastern Asia actually turned less green over the years. Drought – possibly brought on by climate change – was the reason those areas bucked the greening trend, Myneni said.

The increased vegetation might help cut greenhouse gases by drawing carbon dioxide out of the atmosphere, depending on the type of vegetation that is gaining ground, Myneni said. More forests could serve as a carbon dioxide "sink," but other vegetation types could make the problem worse.

The study was funded by the National Atmospheric Space Administration's Earth Science Enterprise, and the National Oceanic and Atmospheric Administration's Office of Global Programs.