Blame for global warming placed firmly on humankind
- Blame for global warming placed firmly on humankind
NewScientist.com news service
Catherine Brahic, Paris
The 2nd of February 2007 will one day hopefully be remembered as the
day the question mark was removed from the debate on whether human
activities are driving climate change, said the head of the UN
Environment Programme at the launch of the most authoritative
scientific report on climate change to date.
The new Intergovernmental Panel on Climate Change report says there
is 90% certainty that the burning of fossil fuels and other human
activities are driving climate change.
"The word unequivocal is the key message of this report," said Achim
Steiner, executive director of UNEP, adding that those who have
doubts about the role of humans in driving the climate "can no longer
ignore the evidence".
The IPCC report says the rise in global temperatures could be as high
as 6.4°C by 2100. The report also predicts sea level rises and
increases in hurricanes. It is the work of 1200 climate experts from
40 countries, who have spent six years reviewing all the available
climate research. It was released in Paris, France, on Friday (read
the 21-page summary here, pdf format). Listen to audio from today's
The last IPCC report, issued in 2001, predicted that temperatures
would rise by 1.4°C to 5.8°C by 2100, relative to 1990 temperatures.
But the new report says temperature rises by 2100 could, in the most
extreme scenarios, range from 1.1°C and 6.4°C. The most likely range
is 1.8°C to 4.0°C (see figure 1, right), with the report predicting
that 4°C is most likely if the world continues to burn fossil-fuels
at the same rate (read the The impacts of rising global
Melting, moving ice
Rises in sea levels are predicted by the new report, threatening low-
lying areas of land around the world. As the oceans warm, their
waters expand, while rising temperatures also increase the melting of
the ice sheets that cover Greenland and Antarctica.
In 2001, the IPCC predicted that sea levels would rise by between 9
88 centimetres by 2100, relative to 1990 levels. The new report says
rises could range from 18 cm to 59 cm. The top end of the range
corresponds to a fossil-fuel intensive future (see A1F1 scenario in
Modelling the future climate: the baseline scenarios).
But predictions of sea level rise are one of the most contentious
areas of the report - very recent research has suggested that rises
of up to 140 cm are possible (see Shorelines may be in greater peril
The problem is that the understanding of how warming affects
Greenland and Antarctic ice sheets remains limited, and they are
predicted to be the most important contributors to change. Estimates
of the straightforward melting of ice are incorporated in the IPCC
report. But warming may also accelerate the movement of ice in
glaciers into the ocean, perhaps by meltwater lubricating the
undersides of ice streams.
Susan Solomon, one of the report's lead authors, said there was no
published research that quantified this effect, and so it was not
included. But she added: "If temperatures exceed 1.9°C to 4.6°C above
pre-industrial temperatures, and were to be sustained for thousands
of years, eventually we would expect the Greenland ice sheet to melt.
That would raise sea level by 7 metres."
Climate change is also expected to affect the frequency and strength
of tropical storms and hurricanes. The latest IPCC report says the
activity of tropical cyclones is "likely" to increase over the 21st
century. It says "likely" indicates a probability of more than 66%.
This is a bolder statement than the World Meteorology Organisation
issued in January.
Precipitation patterns will change too by 2100, according to IPCC
predictions (see figure 2, right). Mid- to high-latitude regions will
see up to 20% more rain and snow, while the tropical regions will see
Humans to blame
Considering the human role in causing climate change, the IPCC report
damning: "The understanding of [human] influences on climate has
improved since the  report, leading to a very high confidence
that human activities" are responsible for most of the warming seen
since 1950, says the report's summary for policymakers. "Very high
confidence" is described as "at least a 9 out of 10 chance of being
Before the industrial revolution, human greenhouse gas emissions were
small, and the atmospheric concentration of carbon dioxide the main
greenhouse gas was about 280 parts per million (ppm).
Thanks largely to the burning of fossil fuels and changes in land
use, such as agricultural exploitation and deforestation, the
atmospheric concentration of carbon dioxide reached 379 ppm in 2005,
says the IPCC.
The IPCC draws together the world's leading climate experts to review
and assess all available research, under the auspices of UN
Environment Programme and the World Meteorology Organization.
The result of their assessment, which is done every five to six
years, establishes what is considered the gold standard of consensus
on climate change science.
The latest IPCC report was written by hundreds of experts and
reviewed by hundreds more, from 113 countries. It is being released
in stages during 2007. The first chapter, released on Friday, deals
with the scientific basis for climate change.
The next two parts of the IPCC's 2007 assessment, plus a synthesis,
will be released throughout the year. Part 2, dealing with the
impacts of climate change and our vulnerability to those impacts,
will be released in April. Part 3, to be released in May, deals with
how we might mitigate these impacts.