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Wednesday, 5 September, 2001, 20:00 GMT 21:00 UK
Satellites show greening planet
The Northern Hemisphere is getting greener
By BBC News Online science editor Dr David Whitehouse

Researchers using satellite data say that plant life above 40 degrees north latitude has been growing more vigorously since 1981.

One suspected cause is rising temperatures, possibly linked to the greenhouse effect.

Eurasia seems to be greening more than North America, with more lush vegetation for longer periods of time.

Summers are also getting longer, by 18 days in Eurasia and 12 days in North America.

Denser vegetation

"When we looked at temperature and satellite vegetation data, we saw that year-to-year changes in growth and duration of the growing season of northern vegetation are tightly linked to year-to-year changes in temperature," said Liming Zhou of the American space agency's (Nasa) Goddard Space Flight Center, Maryland.

"The area of vegetation has not extended, but the existing vegetation has increased in density," he adds.

The researchers also looked at the differences in vegetation growth between North America and Eurasia, because the pattern and extent of warming are different on the two continents.

The Eurasian greening was especially persistent over a broad swath of land from central Europe through Siberia to far-east Russia, where most of the vegetation is forests and woodlands.

Longer summers

By comparison, North America shows a fragmented pattern of change, notable only in the forests of the east and grasslands of the upper Midwest.

Dramatic changes in the timing of both the appearance and fall of leaves are recorded in these two decades of satellite data.

In Eurasia, the growing season is now almost 18 days longer, on average, with spring arriving a week early and autumn delayed by 10 days.

In North America, the growing season appears to be as much as 12 days longer.

'Carbon sinks'

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

Carbon dioxide is an important greenhouse gas and is thought to play a major role in rising global temperatures.

Myneni added that under the Kyoto Protocol, most of the developed countries in the North could use certain vegetation "carbon sinks" to meet their greenhouse gas emissions reduction commitments.

If the northern forests are greening, they may already be absorbing carbon, he said: "As to how much and for how long, that needs more research."

The research will appear in the Journal of Geophysical Research published by the American Geophysical Union.

See also:

25 Feb 99 | Europe
Summers are getting longer
11 May 01 | Americas
Global warming helps Arctic animals
08 Sep 00 | Sci/Tech
Ice records reveal warming trend
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