Landmark UN study backs
2,000 scientists all but end the debate: Human activity
causes global warming
By Peter Gorrie
Star " -- -- A major new United
Nations report shows global scientists are more
convinced than ever that human activity is causing
climate change, the Toronto Star has learned.
The rate of warming between now and 2030 is likely to be
twice that of the previous century, it says.
And it concludes that most of the global warming since
the middle of the last century has been caused by
man-made greenhouse gases.
The report, to be released in Paris Feb. 2, should all
but end any debate on climate change and compel
governments and industries to take urgent measures to
deal with it, scientists say.
"It is very likely that (man-made) greenhouse gas
increases caused most of the globally average
temperature increases since the mid-20th century,"
states the report of the Intergovernmental Panel on
In the clinical language of science, it paints a stark
picture of the effects of greenhouse gas emissions:
"Discernible human influences now extend to other
aspects of climate, including continental average
temperatures, atmospheric circulation patterns and some
types of extremes."
It is "very likely that hot extremes, heat waves and
heavy precipitation events will continue to become more
frequent." Storm tracks will move from the tropics
toward the poles.
The widely anticipated report is the fourth by the IPCC,
which every few years publishes the definitive
conclusions of about 2,000 scientists who are recognized
as experts in their respective fields. Each one has
moved closer to closing debate on the causes and effects
of climate change.
The portion of the report obtained by the Star is called
the final draft of the "Summary for Policy Makers."
The summary states that the warming effect of greenhouse
gases increased by 20 per cent during the past decade –
"the largest change observed or inferred for any decade
in at least the last 200 years."
Global warming would be even greater had it not been
slowed by other forms of pollution that stopped some of
the sun's energy from reaching the Earth.
Rebutting one of the main arguments of climate change
skeptics, it says observations of temperature increases
and shrinking ice cover, "support the conclusion that it
is extremely unlikely that global climate change of the
past 50 years" was caused by solar flares or other
Eleven of the past 12 years have been the hottest in
Earth's recent history, it says.
All the continents except Antarctica have warmed during
the past half-century, with the biggest impacts in
Canada's Arctic and other northern regions.
Research since the third report was released in 2001
increases the certainty about climate change and the
likely scale of most of its effects, including warmer
temperatures and severe weather, the report states.
One crucial prediction has been made a bit less
worrying: Although sea level is rising – for now, mainly
because the oceans are warming to a depth of at least
3,000 metres, and expanding – the estimates for how much
it will go up have been lowered.
The summary also notes that there has been, as yet,
little change in the North Atlantic Drift, the warm
current that gives Britain and northern Europe a
relatively temperate climate and that is expected to
slow, or stop, as climate change alters the ocean.
It will slow, but not abruptly during the coming
century, the report says.
For the most part, though, the conclusions point in a
"Warming of the climate system is unequivocal."
The report estimates that if the amount of carbon
dioxide in the atmosphere could be kept below 550 parts
per million – which would take a major worldwide effort
to cut greenhouse gas emissions – the average global
temperature would rise by 2 to 4.5 degrees Celsius above
the level before the Industrial Revolution started about
250 years ago.
The current carbon level is about 380 parts per million
and rising steadily, compared with 280 at the time
humans began burning large amounts of coal, oil and
other fossil fuels.
The temperature estimate depends on which combination of
computer model and research data is used.
The upper forecast is higher than in previous reports.
"Values higher than 4.5 C cannot be excluded" because of
"feedbacks," such as the increased ability of the
atmosphere to absorb water vapour – an extremely potent
greenhouse gas – as it heats up, and the greater warmth
absorbed as Arctic ice melts.
Regional forecasts of climate change effects are better
than in the previous report, and they predict the
greatest warming at northern latitudes and high
altitudes, and the least over the North Atlantic and the
The north faces the biggest increase in precipitation.
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