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Warming 'very likely' human-made Humans blamed for climate change
(about 23 hours later)
Climatic changes seen around the world are "very likely" to have a human cause, the Intergovernmental Panel on Climate Change (IPCC) will conclude. Global climate change is "very likely" to have a human cause, an influential group of scientists has concluded.
By "very likely", the IPCC means greater than 90% probability. The Intergovernmental Panel on Climate Change (IPCC) said temperatures were probably going to increase by 1.8-4C (3.2-7.2F) by the end of the century.
The scientific body has spent this week finalising its positions on key issues, notably forecasts of sea level rise, as it prepares to publish a major report. It also projected that sea levels were most likely to rise by 28-43cm, and global warming was likely to influence the intensity of tropical storms.
But a new study released on the eve of publication suggests its previous reports may have been too conservative. The findings are the first of four IPCC reports to be published this year.
There is no doubt that for this period, the climate has been changing faster than the IPCC predicted Stefan Rahmstorf "We can be very confident that the net effect of human activity since 1750 has been one of warming," co-lead author Dr Susan Soloman told delegates in Paris.
Research by an international group of scientists suggests that temperatures and sea levels have been rising at or above the maximum rates proposed during the last IPCC report in 2001.
The first part of the Panel's 2007 assessment will be formally released on Friday morning here in Paris.
Strong languageStrong language
Some of the language which the agency has agreed it will use to assess humanity's influence on climatic change this time is stronger than it has used previously. The report, produced by a team tasked with assessing the science of climate change, was intended to be the definitive summary of climatic shifts facing the world in the coming years. IPCC PROJECTIONS Probable temperature rise between 1.8C and 4CPossible temperature rise between 1.1C and 6.4CSea level most likely to rise by 28-43cmArctic summer sea ice disappears in second half of centuryIncrease in heatwaves very likely Increase in tropical storm intensity likely class="" href="/1/hi/sci/tech/6323653.stm">IPCC report: World reaction class="" href="/1/hi/sci/tech/6324093.stm">IPCC report: UK reaction
In 2001, it was "likely" that human activities lay behind the trends observed at various parts of the planet; "likely" in IPCC terminology means "between 66% and 90%". The agency said that it would use stronger language to assess humanity's influence on climatic change than it had previously done.
Now, the Panel concludes, it is at least 90% certain that human emissions of greenhouse gases rather than natural variations are warming the planet's surface. In 2001, it said that it was "likely" that human activities lay behind the trends observed at various parts of the planet; "likely" in IPCC terminology means between 66% and 90% probability.
class="" href="/1/hi/sci/tech/6320515.stm">How computers model climate "This report closes the doors to those who were able to detract from the issue, and puts an end to the notion of uncertainty and doubt about man's role in climate change," commented United Nations Environment Programme executive director Achim Steiner. Now, the panel concluded that it was at least 90% certain that human emissions of greenhouse gases rather than natural variations are warming the planet's surface.
On key scientific questions - how much the Earth's surface will warm by, and how high sea levels will rise - the experts have been locked in discussion. They projected that temperatures would probably rise by between 1.8C and 4C, though increases as small as 1.1C (2F) or as large as 6.4C (11.5F) were possible.
It is widely believed they will predict an average global temperature rise by the end of the century of between about 2C and 4.5C, without ruling out higher numbers completely. In 2001, using different methodology, the numbers were 1.4 (2.5F) and 5.8C (10.4F).
On sea level, there is a more fundamental debate. Computer models of climate do not generally include water coming into the oceans as icecaps melt; so should the IPCC exclude this from its calculations, or estimate the effect of a process which scientists do not understand well, but which could have a big impact? class="" href="/1/hi/sci/tech/6320515.stm">How computers model climate
There is likely to be some backing for a theory which has proved highly controversial in recent years, with the IPCC set to conclude that it is likely - meaning a greater probability than 66% - that rising temperatures have contributed to more powerful tropical storms in some areas of the world. On sea level, there has been a more fundamental debate.
Computer models of climate do not generally include water coming into the oceans as ice caps melt. So the IPCC had to decide whether to exclude this from its calculations, or to estimate the effect of a process which scientists do not understand well but which could have a big impact.
They used the former, more conservative approach, projecting an average rise in sea levels globally of between 28 and 43cm. The 2001 report cited a range of nine to 88cm.
As for climate change influencing the intensity of tropical storms in some areas of the world, the IPCC concluded that it was likely - meaning a greater probability than 66% - that rising temperatures were a factor.
'Unequivocal'
Climate change: In graphics
Dr Rajendra Pachauri, the IPCC chairman, said: "It is extremely encouraging in that the science has moved on from what was possible in the Third Assessment Report.
"If you see the extent to which human activities are influencing the climate system, the options for mitigating greenhouse gas emissions appear in a different light, because you can see what the costs of inaction are," he told delegates in Paris.
Achim Steiner, executive director of the United Nations Environment Programme (Unep), said the findings marked a historical landmark in the debate about whether humans were affecting the state of the atmosphere.
READ THE FINDINGS IPCC report [2.2MB] Most computers will open this document automatically, but you may need Adobe Reader Download the reader here "It is an unequivocal series of evidence [showing that] fossil fuel burning and land use change are affecting the climate on our planet."
He added: "If you are an African child born in 2007, by the time you are 50 years old you may be faced with disease and new levels of drought."
He said that he hoped the IPCC report would galvanise national governments into action.
At varianceAt variance
As discussions entered their final phase, the journal Science published a study comparing the IPCC's 2001 projections on temperature and sea level change with what has actually happened. But a study published on the eve of the IPCC report suggested that the international body's previous reports may have actually been too conservative.
IPCC models start from the year 1990, so that gives 16 years of data to compare. HAVE YOUR SAY The IPCC have put together a compelling case that drastic and immediate action is needed Steve Easterbrok, Toronto class="" href="http://newsforums.bbc.co.uk/nol/thread.jspa?threadID=5386&edition=1">Send us your views
The models had forecast a temperature rise between about 0.15C and 0.35C over this period. The actual rise of 0.33C is very close to the top of the IPCC's range. Writing in the journal Science, an international group of scientists concluded that temperatures and sea levels had been rising at or above the maximum rates proposed in the last report, which was published in 2001.
A new study suggest warming is outpacing earlier forecastsA more dramatic picture emerges from the sea level comparison. The paper compared the 2001 projections on temperature and sea level change report with what has actually happened.
The actual average level, measured by tide gauges and satellites, has risen faster than the IPCC predicted it would due to simple thermal expansion of seawater, and at the maximum which the scientific body considered possible if its estimates for the melting of land-based glaciers and ice sheets were included. The models had forecasted a temperature rise between about 0.15C-0.35C (0.27-0.63F) over this period. The actual rise of 0.33C (0.59F) was very close to the top of the IPCC's range.
"Our intention with this study was to demonstrate how temperatures and sea levels have actually gone up," said study leader Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research in Germany, "because 'climate sceptics' have cast doubt on IPCC projections and whether they are exaggerated." A more dramatic picture emerged from the sea level comparison. The actual average level, measured by tide gauges and satellites, had risen faster than the intergovernmental panel of scientists predicted it would.
The group suggests that if anything, the IPCC has been conservative. The IPCC's full climate science report will be released later in the year, as will other chapters looking at the probable impacts of climate change, options for adapting to those impacts, and possible routes to reducing emissions of greenhouse gases.
The most obvious cause of the discrepancy - a faster-than expected rise in carbon dioxide concentrations - is ruled out, as the observed CO2 rise has mimicked model projections fairly well.
Another explanation could be that the effect on temperature of increasing carbon dioxide levels in the atmosphere - the factor called "climate sensitivity" - is higher than scientists had believed when they built their computer models.
Alternatively it could be natural climate variability.
"We cannot conclude the exact cause," commented Professor Rahmstorf, "but there is no doubt that for this period, the climate has been changing faster than the IPCC predicted."
HAVE YOUR SAY Who is going to tell a billion people that they can't have air-conditioning or an automobile? Tooba, Rockville, USA Send us your views Together with his co-researchers on this project, Professor Rahmstorf is in Paris for the IPCC discussions, which will on Friday morning end with the release of summary conclusions on the current state of climate science, drawing on the work of thousands of researchers.
The full climate science report will be released later in the year, as will other IPCC chapters looking at the probable impacts of climate change, options for adapting to those impacts, and possible routes to reducing emissions of greenhouse gases.
Richard.Black-INTERNET@bbc.co.ukRichard.Black-INTERNET@bbc.co.uk