Warming: The Vicious Circle
By Steve Connor
30 January 2007
effects of man-made emissions of carbon dioxide are being felt on every
inhabited continent in the world with very different parts of the climate
now visibly responding to human activity.
These are among the main
findings of the most intensive study of climate change by 2,000 of the
world's leading climate scientists. They conclude that there is now
little doubt that human activity is changing the face of the planet.
In addition to rising surface
temperatures around the world, scientists have now linked man-made emissions
of greenhouse gases to significant increases in ocean temperatures,
rises in sea levels and the dramatic melting of Arctic sea ice over
the past 35 years.
A draft copy of the fourth
report of the Intergovernmental Panel on Climate Change (IPCC) says
that global temperature rises this century of between 2C and 4.5C are
almost inevitable. Ominously, however, it also says that much higher
increases of 6C "or more" cannot be ruled out.
The final version of the
IPCC's latest report is to be published on Friday but a draft copy,
seen by The Independent, makes it clear that climate change could be
far worse than previously thought because of potentially disastrous
"positive" feedbacks which could accelerate rising temperatures.
A warmer world is increasing
evaporation from the oceans causing atmospheric concentrations of water
vapour, a powerful greenhouse agent, to have increased by 4 per cent
over the sea since 1970. Water vapour in the atmosphere exacerbates
the greenhouse effect. This is the largest positive feedback identified
in the report, which details for the first time the IPCC's concern over
the uncertainties - and dangers - of feedback cycles that may quickly
accelerate climate change.
All the climate models used
by the IPCC also found that rising global temperatures will erode the
planet's natural ability to absorb man-made CO2. This could lead to
CO2 concentrations in the atmosphere rising by a further 44 per cent,
causing global average temperatures to increase by an additional 1.2C
The IPCC's Fourth Assessment
Report will go further than any of its three previous reports in linking
the clear signs of global climate change with increases in man-made
emissions of CO2 and other greenhouse gases since the start of the Industrial
"Confidence in the assessment
of the human contributions to recent climate change has increased considerably
since the TAR [Third Assessment Report]," says the draft report.
This is due to the stronger signs of climate change emerging from longer
and more detailed records and scientific observations, it says.
The "anthropogenic signal"
- the visible signs of human influence on the climate - has now emerged
not just in global average surface temperatures, but in global ocean
temperatures and ocean heat content, temperature extremes on the land
and the rapidly diminishing Arctic sea ice. "Anthropogenic warming
of the climate system is widespread and can be detected in temperature
observations taken at the surface, in the free atmosphere and in the
oceans," the draft report says. "It is highly likely [greater
than 95 per cent probability] that the warming observed during the past
half century cannot be explained without external forcing [human activity]."
The report adds that global
warming over the past 50 years would have been worse had it not been
for the counterbalancing influence of man-made emissions of aerosol
pollutants, tiny airborne particles that reflect sunlight to cause atmospheric
cooling. "Without the cooling effect of atmospheric aerosols, it
is likely that greenhouse gases alone would have caused more global
mean temperature rise than that observed during the last 50 years,"
the draft report says.
"The hypothetical removal
from the atmosphere of the entire current burden of anthropogenic sulphate
aerosol particles would produce a rapid increase of about 0.8C within
a decade or two in the globally averaged temperature."
The IPCC says that over the
coming century we are likely to see big changes to the Earth's climate
system. These include:
* Heat waves, such as the
one that affected southern Europe in summer 2003, are expected to be
more intense, longer-lasting and more frequent.
* Tropical storms and hurricanes
are likely to be stronger, with increased rainfall and higher storm
surges flooding coastlines.
* The Arctic is likely to
become ice free in the summer, and there will be continued melting of
mountain glaciers, ice caps and ice sheets.
* Sea levels will rise significantly
even if levels of CO2 are stabilised. By 2100 sea levels could be 0.43
metres higher on average than present, and by 2300 they could be up
to 0.8 metres higher.
The IPCC also finally nails
the canard of the climate sceptics who argue that global warming is
a myth or the result of natural climate variability; natural factors
alone cannot account for the observed warming, the IPCC says. "These
changes took place at a time when non-anthropogenic forcing factors
(i.e. the sum of solar and volcanic forcing) would be expected to have
produced cooling, not warming.
"There is increased
confidence that natural internal variability cannot account for the
observed changes, due in part to improved studies demonstrating that
the warming occurred in both oceans and atmosphere, together with observed
ice mass losses."
The report, the first draft
of which was formulated last year, will be made public on Friday in
Key findings of the IPCC's
fourth assessment report
* Global temperatures continue
to rise with 11 of the 12 warmest years since 1850 occurring since 1995.
Computer models suggest a further rise of about 3C by 2100, with a 6C
rise a distant possibility
* It is virtually certain
(there is more than a 99 per cent probability) that carbon dioxide levels
and global warming is far above the range of natural variability over
the past 650,000 years
* It is virtually certain
that human activity has played the dominant role in causing the increase
of greenhouse gases over the past 250 years
* Man-made emissions of atmospheric
aerosol pollutants have tended to counteract global warming, which otherwise
would have been significantly worse
* The net effect of human
activities over the past 250 years has very likely exerted a warming
influence on the climate
* It is likely that human
activity is also responsible for other observed changes to the Earth's
climate system, such as ocean warming and the melting of the Arctic
* Sea levels will continue
to rise in the 21st Century because of the thermal expansion of the
oceans and loss of land ice
* The projected warming of
the climate due to increases in carbon dioxide during the 21st Century
is likely to cause the total melting of the Greenland ice sheet during
the next 1,000 years, according to some computer forecasting models
* The warm Gulf Stream of
the North Atlantic is likely to slow down during the 21st Century because
of global warming and the melting of the freshwater locked up in the
Greenland ice sheet. But no models predict the collapse of that warm
current by 2100.
© 2006 Independent News
and Media Limited
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