Global Warming: The vicious circle
By Steve Connor, Science Editor
Published: 29 January 2007
The Independent
The 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 by 2100.
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 Revolution.
"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 Paris.
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 ice
* 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.