Greener Earth means good news and bad

A graphic showing the greening of the Earth: Purple, red and green depict areas where the most greening is taking place.

By Janis Winogradsky
CNN

WASHINGTON (CNN) -- Parts of Earth's Northern Hemisphere have become much greener over the past 21 years, a trend scientists attribute to rising temperatures, according to a recently released study.

Researchers using satellite data confirmed that plant life found above 40 degrees north latitude -- a line that stretches across New York to Madrid to Beijing -- is growing more vigorously, and the growing season has been extended by an average of two weeks per year in some parts of the world.

"The up side is that Russia and Canada will have a longer growing season, and can grow more crops," according to Compton Tucker, a NASA scientist and one of the authors of the NASA-funded study.

That's the good news.

The bad news, the scientists said, is the suspected cause for all this greenery is rising temperatures, linked to the buildup of greenhouse gases in the atmosphere. Carbon dioxide, the main greenhouse gas, is suspected of playing a role in rising global temperatures.

"This is an important finding because of possible implications to the global carbon cycle," said Ranga Myneni, a researcher with Boston University.

The study is scheduled to be published in the September 16 issues of the Journal of Geophysical Research-Atmospheres. Advance copies of the study were released to the news media.

Researchers said that if northern forests are greening, they may be absorbing carbon -- a process that can impact global temperature changes and further evidence of global warming.

Scientists also looked at the differences in vegetation growth between North America and Eurasia because the patterns and magnitudes of warming are different on the two continents. They linked temperature data from thousands of meteorological stations with the greenness data from orbiting weather satellites. The equation is simple - the warmer the temperature, the more dense the vegetation.

Researchers also noted "dramatic changes" in the timing of the appearance and fall of leaves in the past two decades: Spring is arriving early, and autumn is delayed by as much as 10 days.