Evidence of human-caused global warming unequivocal

Posted: 2 February 2007

Changes in the atmosphere, the oceans, glaciers and ice caps show unequivocally that the Earth is warming, according to the first global assessment of climate change science in six years, the Environment News Service reports.

The [IPCC] report confirms that the observed increase in atmospheric concentrations of greenhouse gases carbon dioxide, methane, and nitrous oxide since 1750 is the result of human activities.

Reftinskaya
Reftinskaya
Greenhouse gases rise into the air from Russia's largest coal-fired power plant, Reftinskaya GRES. Photo courtesy RAO UESR.
The Intergovernmental Panel on Climate Change, IPCC, concludes that advances in climate modelling and the collection and analysis of data now give scientists 90 per cent confidence in their understanding of how human activities are causing the world to warm. This level of confidence is much greater than what could be achieved in 2001 when the IPCC issued its last assessment.

Introducing the report today in Paris, Dr. Susan Solomon, an American atmospheric chemist, said it is "very likely," a 90 per cent probability, that most of the observed increase in temperatures is due to the observed increase in greenhouse gas concentrations. The 2001 assessment said it was "likely," a probability of 66 per cent. The rapid rise in global concentrations of carbon dioxide, methane and nitrous oxide, all greenhouse gases, is so different from the patterns for thousands of years previous, "there is no doubt that increase is dominated by human activity," said Solomon, who helped to identify the mechanism that created the Antarctic ozone hole.

A unique process

IPCC Chairman Dr R K Pachauri
IPCC Chairman Dr R K Pachauri
IPCC Chairman Dr R K Pachauri. Photo courtesy US Climate Change Science Program
IPCC Chairman Dr. R.K. Pachauri of India called the entire process of preparing the document, the first of four to be released this year by the panel, "a unique example of science in the service of society."

He said 600 authors from 40 countries worked on the report, which was then assessed by 600 reviewers. Over the past several days, the whole thing was discussed by 300 delegations from 113 countries meeting in Paris. "This is the strength of the IPCC process," said Dr. Pachauri. The scientists provide the knowledge, this is discussed and adopted by governments. It provides credibility."

The report describes an accelerating transition to a warmer world marked by more extreme temperatures, heat waves, new wind patterns, worsening drought in some regions, heavier precipitation in others, melting glaciers and Arctic ice, and rising global average sea levels.

For the first time, the report provides evidence that the ice sheets of Antarctica and Greenland are losing mass and contributing to sea level rise.

An even greater degree of warming would likely have occurred if emissions of pollution particles and other aerosols had not offset some of the impact of greenhouse gases, by reflecting sunlight back out to space, the scientists said.

Warming for centuries

Solomon said the concentrations of greenhouse gases already in the atmosphere will continue to warm the planet for centuries, even if humans stabilize emissions within the next 10 years.

"This report by the IPCC represents the most rigorous and comprehensive assessment possible of the current state of climate science and has considerably narrowed the uncertainties of the 2001 report," said Michel Jarraud, secretary general of the World Meteorological Organization, WMO.

"While the conclusions are disturbing, decision makers are now armed with the latest facts and will be better able to respond to these realities," Jarraud said. "The speed with which melting ice sheets are raising sea levels is uncertain, but the report makes clear that sea levels will rise inexorably over the coming centuries. It is a question of when and how much, and not if," he said.

"In our daily lives we all respond urgently to dangers that are much less likely than climate change to affect the future of our children," said Achim Steiner, executive director of the United Nations Environment Programme, UNEP, which, together with the WMO, established the Intergovernmental Panel on Climate Change in 1988.

"February 2nd will be remembered as the date when uncertainty was removed as to whether humans had anything to do with climate change on this planet," said Steiner. "We are looking for an unequivocal response from politicians. The evidence is on the table, we no longer have to debate that part of it.

"Nine thousand children will be born worldwide during this one hour press conference," said Steiner, "and it differs where you are born. African children will be faced with new diseases, new droughts, may have to leave their homes because Africa may have 30 per cent of its coastal infrastructure destroyed by sea level rise."

Many environmetnal refugees

Many Asians will be turned into environmental refugees as rising sea levels claim their lands, Steiner warned. "The implications of global warming over the coming decades for our industrial economy, water supplies, agriculture, biological diversity and even geopolitics are massive," he said.

"Momentum for action is building," Steiner said. "This new report should spur policymakers to get off the fence and put strong and effective policies in place to tackle greenhouse gas emissions."

New warming estimates

The IPCC Working Group I report, The Physical Science Basis concludes that:

  • If atmospheric concentrations of greenhouse gases double compared to pre-industrial levels, this would "likely" cause an average warming of around 3°C (5.4°F), with a range of 2 to 4.5°C (3.6 - 8.1°F).

    For the first time, the IPCC is providing best estimates for the warming projected to result from particular increases in greenhouse gases that could occur after the 21st century, along with uncertainty ranges based on more comprehensive modelling.

  • A greenhouse gas level of 650 parts per million (ppm) would "likely" warm the global climate by around 3.6°C, while 750 ppm would lead to a 4.3°C warming, 1,000 ppm to 5.5°C and 1,200 ppm to 6.3°C. Future greenhouse gas concentrations are difficult to predict and will depend on economic growth, new technologies and policies and other factors.

  • The world's average surface temperature has increased by around 0.74°C over the past 100 years (1906 - 2005). This figure is higher than the 2001 report's 100-year estimate of 0.6°C due to the recent series of extremely warm years, with 11 of the last 12 years ranking among the 12 warmest years since modern records began around 1850.
Hurricane Dennis
Hurricane Dennis
Hurricane Dennis flooded this coastal road in North Carolina. 1999. Global warming is predicted to bring more severe weather events. Photo © Dave Gatley courtesy FEMA.

  • A warming of about 0.2°C is projected for each of the next two decades.

    The best estimates for sea-level rise due to ocean expansion and glacier melt by the end of the century (compared to 1989 - 1999 levels) have narrowed to 28 - 58 cm, versus 9 - 88 cm in the 2001 report, due to improved understanding. However, larger values of up to one metre (39 inches) by 2100 cannot be ruled out if ice sheets continue to melt as temperature rises. The last time the polar regions were significantly warmer than at present for an extended period, about 125,000 years ago, reductions in polar ice volume caused the sea level to rise by four to six metres.

Shrinking sea ice
  • Sea ice is projected to shrink in both the Arctic and Antarctic regions. Large areas of the Arctic Ocean could lose year-round ice cover by the end of the 21st century if human emissions reach the higher end of current estimates.

    The extent of Arctic sea ice has already shrunk by about 2.7 per cent per decade since 1978, with the summer minimum declining by about 7.4 per cent per decade.

  • Snow cover has decreased in most regions, especially in spring. The maximum extent of frozen ground in the winter/spring season decreased by about 7 per cent in the Northern Hemisphere over the latter half of the 20th century.

    The average freezing date for rivers and lakes in the Northern Hemisphere over the past 150 years has arrived later by some 5.8 days per century, while the average break-up date has arrived earlier by 6.5 days per century.

  • It is "very likely" that precipitation will increase at high latitudes and "likely" it will decrease over most subtropical land regions. The pattern of these changes is similar to what has been observed during the 20th century.

  • It is "very likely" that the upward trend in hot extremes and heat waves will continue. The duration and intensity of drought has increased over wider areas since the 1970s, particularly in the tropics and subtropics. The Sahel, the Mediterranean, southern Africa and parts of southern Asia have already become drier during the 20th century.

  • The amounts of carbon dioxide and methane now in the atmosphere far exceed pre-industrial values going back 650,000 years. Concentrations of carbon dioxide have already risen from a pre-industrial level of 280 ppm to around 379 ppm in 2005, while methane concentrations have risen from 715 parts per billion (ppb) to 1,774 in 2005.

  • A number of widely discussed uncertainties have been resolved. The temperature record of the lower atmosphere from satellite measurements has been reconciled with the ground-based record. Key remaining uncertainties involve the roles played by clouds, glaciers and ice caps, oceans, deforestation and other land-use change, and the linking of climate and biogeochemical cycles.

The Intergovernmental Panel on Climate Change does not conduct new research. Instead, its mandate is to make policy relevant assessments of the existing worldwide literature on the scientific, technical and socio-economic aspects of climate change.

Its reports have played a major role in inspiring governments to adopt and implement the United Nations Framework Convention on Climate Change and the Kyoto Protocol.

The Summary for Policymakers for IPCC Working Group I, which was agreed line-by-line by governments during the course of this week, has now been posted in English at www.ipcc.ch The full underlying report - "Climate Change 2007: The Physical Science Basis" - will be published by Cambridge University Press.

The Working Group II report on climate impacts and adaptation will be launched in Brussels on April 6. The Working Group III report on mitigation will be launched in Bangkok on May 4.

A Synthesis Report will be adopted in Valencia, Spain on November 16. Dr. Pachauri says this 30 page synthesis of the three Working Group reports will make it possible for a prime minister, a president or a CEO to understand it during a train ride from Paris to Brussels or wherever they are travelling.

Together, the four volumes will make up the IPCC's fourth assessment report. Previous reports were published in 1990, 1995 and 2001. (Copyright Environment News Service (ENS) 2006. All Rights Reserved.)