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Climate change boom or bust for biodiversity?
Will climate change trigger mass extinctions or will new life
bloom in its wake?
Some of the scientific scenarios are apocalyptic and see a
warmer world leading to the most profound changes since the
demise of the dinosaurs.
“The biodiversity and nature impacts (of global warming) are
well-documented...all the signals are there: birds migrating
earlier, flowers blooming earlier, seasons changing,” said
Jennifer Morgan, director of the Climate Change Program for
the conservation group WWF International.
Global warming could wipe out a quarter of all species of
plants and animals by 2050, according to one international
study.
Others see a wetter and hence greener world as a result.
Australians scientists said this month that a hotter planet
could induce more rainfall, encouraging the growth of plants
that soak up greenhouse gases.
Many scientists say any benefits to forest growth could not
offset threats to biodiversity from human pollution, the
spread of roads and cities or rising sea levels tied to global
warming.
Few scientists dispute the basic premise of the “greenhouse
effect,” which holds that human-induced carbon dioxide
emissions are trapping heat in the Earth’s atmosphere.
The debate intensifies when scientists attempt to forecast how
fast and how far global temperatures will rise as a result.
One dramatic thesis asserts that humanity has been altering
the Earth’s climate for the past 8,000 years because of
large-scale forest clearance for agriculture, which released
huge amounts of greenhouse gas into the atmosphere.
In a paper published last year in the journal “Climatic
Change,” William Ruddiman of the University of Virginia in
Charlottesville argued that on the eve of Industrial
Revolution two centuries ago, people had already raised the
global temperature by an average of 0.8 degrees centigrade.
“The first phase is that of negligible human impact which
stretches back, say, a million years ago. And then you have
this middle phase which begins 8,000 years ago with early
agriculture and greenhouse gas levels rise slowly,” Ruddiman
told Reuters by telephone.
“And since the Industrial Revolution there is a real
acceleration (in greenhouse gas emissions) and as a result a
stronger effect on climate,” he said.
Ruddiman says that pre-industrial greenhouse gas emissions
warmed the planet sufficiently to stop an ice age in its
tracks.
And the cause — widespread forest clearing — would almost
certainly have had an impact on biodiversity, though Ruddiman
himself has not speculated on this angle, and declined to be
drawn on it as it is not his field of expertise.
Habitat destruction is widely regarded by many ecologists as
the biggest man-made reason for species loss or extinction.
Forest clearing in Europe 5,000 years ago would not be like
the mechanized felling of tropical forests today.
It may in fact have initially contributed to diversity as
early farmers would probably have left a variety of habitats
in their wake, such as fields bordering forests, which could
have benefited many species.
There is an intriguing flip side to this story.
Ruddiman maintains that this pre-industrial warming trend was
at times reversed by reforestation in the northern hemisphere
— a process set in motion by mass human deaths caused by
pandemics of bubonic plague and other diseases.
His argument: the plague led to widespread abandonment of
farms during the Roman empire and most spectacularly in the
mid-14th century, when at least one third of Europe’s
inhabitants perished in its wake between 1347 and 1350.
Cultivated land also fell into disuse in the Americas because
of smallpox, which devastated Native American populations as a
result of their initial contacts with Europeans.
The result: forests grew back and absorbed big enough
quantities of greenhouse gases while they were at it to affect
global climate patterns.
“Land-use modellers note that abandoned cropland and pasture
reverts to full-forest carbon levels in 50 years or less,”
Ruddiman wrote.
“Historical records indicate that reoccupation of farms
occurred in less than a century if the plagues quickly abated,
but could be delayed by a century or two if repeated outbreaks
kept population levels low.”
This, he maintains, may have been a factor behind the “Little
Ice Age” between 1300 and 1900.
Ruddiman has since changed his emphasis.
“Since I wrote the paper, I have come to the conclusion that a
bigger impact was the fact that the...plagues stopped the
process of deforestation (by killing off people who would have
contributed to the process),” he said.
Regardless, the process of reforestation would also almost
certainly have had an impact on wildlife — and the plague
would have reduced the number of people in the countryside who
supplemented their diets by hunting.
Reforestation could, if examples in Eastern Europe and the
northeastern U.S. and Canada are anything to go by, have
initially encouraged a greater diversity of life, as the
process of deforestation was set in reverse, with fields
gradually being reclaimed by a variety of wild plant species.
In short, the causes of human-induced climate change — never
mind its effects — have probably already affected life on
Earth in ways that scientists are only beginning to
understand.
And in today’s world of six billion people — compared with
200-400 million 2,000 years ago, according to U.N. estimates —
the causes of climate change may be having a far greater
impact than at any other time in human history.
Pollution linked to the burning of greenhouse fossil fuels and
the destruction of tropical rain forests are, in the view of
most ecologists, taking a serious toll on the environment.
The impact of drastic climate change itself on biodiversity
may hold surprises which have not yet been imagined. reuters.
Curtesy: Daily times
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Pakissan.com;
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