Washington, Dec 11 (IANS): A 13-year decline in vegetation in the eastern and southeastern Amazon has been linked to a decade-long rainfall decline in the region, finds a NASA-funded study.

The findings suggest that the potential loss of vegetation and the associated loss of carbon storage may speed up global climate change.

The study was based on a new way to measure the 'greenness' of plants and trees using satellites.

While one NASA satellite measured up to 25 percent decline in rainfall across two thirds of the Amazon from 2000 to 2012, a set of different satellite instruments observed a 0.8 percent decline in greenness.

While the decline of green vegetation was small, the area affected was not: 5.4 million sq km - equivalent to over half of the area of continental US.

The Amazon's tropical forests are one of the largest sinks for atmospheric carbon dioxide on the planet.

"In other words, if greenness declines, this is an indication that less carbon will be removed from the atmosphere. The carbon storage of the Amazon basin is huge and losing the ability to take up as much carbon could have global implications for climate change," explained lead author Thomas Hilker, remote sensing specialist at Oregon State University in Corvallis, Oregon.

The Amazon basin stores an estimated 120 billion tonnes of the earth's carbon - which is about three times more carbon than humans release into the atmosphere every year.

If vegetation becomes less green, it would absorb lesser carbon dioxide.

"As a result, more of human emissions would remain in the atmosphere, increasing the greenhouse effect that contributes to global warming and alters Earth's climate," the authors noted.

The study appeared in the journal Proceedings of the National Academy of Sciences.