|
The real 'greenhouse
effect'
By Roger Highfield, Science
Editor
(Filed: 06/06/2003)
The world has become a greener place in the past two
decades as a result of climate change, according to a major study
published today.
As the climate has warmed, the Earth has become more
lush and rich with vegetation, notably in the Amazon rainforests,
according to a study jointly funded by the US space agency Nasa and
the US Department of Energy.
The research, published today in the journal Science,
describes how global warming has allowed plants to flourish where
climatic conditions previously limited growth.
In general, where temperatures restricted plant
growth, it became warmer; where sunlight was needed, clouds
dissipated; and where it was too dry, it rained more.
In the Amazon, plant growth was limited by
sun-blocking cloud cover, but the skies have become less cloudy. In
India, where a billion people depend on rain, the monsoon was more
dependable in the 1990s than in the 1980s.
"Our study proposes climatic changes as the leading
cause for the increases in plant growth over the last two decades,
with lesser contribution from carbon dioxide fertilisation and
forest regrowth," said Dr Ramakrishna Nemani, the study's lead
author from the University of Montana, Missoula.
The data suggest that environmentalists may have
overstated the impact of the destruction of forests. "The role of
deforestation may have been overplayed a bit," he told The
Telegraph. However, he added: "The role of deforestation is a
difficult one for us to address in this study.
"What our study shows is that the intact forests have
been taking advantage of the favourable conditions. In this context,
it is all the more important to protect the intact forests. I
believe ultimately what people may do to these forests is a lot more
important than what climate can do."
The past two decades have been the warmest recorded,
but whether this is due to long-term trends - the greenhouse effect
- or short-term trends is unclear: there were three intense El Nino
events, in 1982-83, 1987-88 and 1997-98; changes in tropical
cloudiness and monsoon dynamics; and an almost 10 per cent rise in
atmospheric carbon dioxide.
Earlier studies of the impact on plants at Boston
University and Nasa's Goddard Space Flight Centre, which contributed
to the new work, reported increased growing seasons and more wood
growth in northern, high-latitude forests.
Although the greening of the globe sounds like good
news, co-author Dr Charles Keeling, of the Scripps Institution of
Oceanography, La Jolla, said the 36 per cent increase in global
population, from 4.45 billion in 1980 to 6.08 billion in 2000,
overshadowed the benefits that might have come from increases in
plant growth.
Previous story: US
to move troops from North Korea artillery threat
|
.gif)
.gif)