It's almost certain: humans caused planet to heat up

The Australian
February 03, 2007

SCIENTISTS are now almost certain temperature increases over the last half of the 20th century were caused by human activity, and have warned of ominous further increases up to 4C by 2100.

The world's most significant weather forecast, released last night in Paris, revealed growing confidence in climate modelling that suggests greenhouse gases are reaching dangerous levels and need to be reduced. The first volume of the fourth assessment report by the UN Intergovernmental Panel on Climate Change has reported similar warming projections to its previous report six years ago.

The new report is based on the results of 23 climate models, a three-fold increase from the seven models used in 2001 to deliver best estimates of temperature increases ranging from 1.8C to 4C. The increased number of models has widened the likely temperature ranges from 1.1C to 6.4C, compared with from 1.4C to 5.8C six years ago.

Significantly, the report finds man-made release of greenhouse gases is more than 90 per cent likely to have caused most of the observable increase in global average temperatures since the mid-20th century, about 0.65C. The range of projected rises in global sea levels is from 0.18m to 0.59m by 2100, driven largely by their expansion from rising water temperatures.

The IPCC also reports greater confidence in the projected patterns of warming and other regional-scale features, including contracting snow cover, shrinking sea ice on the poles and the high likelihood of more frequent hot extremes, heatwaves and heavy rainfall patterns.

The Antarctic ice sheets are predicted to remain too cold for widespread surface melting and are expected to gain in mass due to increased snowfall. While the Greenland ice sheet is projected to contribute to sea-level rises after 2100, the report says this will need to be sustained for millenniums to result in its complete elimination and a resulting sea-level rise of about 7m.

The report predicts the emission of carbon dioxide this century will contribute to global warming and sea-level rises for the next millennium. The report predicts increasing intensity in cyclones, including higher peak wind speeds and more heavy rain patterns, but with the possibility of a reduction in their frequency.

Other storms are likely to track towards the poles as the world's weather systems adapt to changes in heat in the atmosphere and deep oceans. Rainfall will shift from the subtropical regions towards the poles. Australian Academy of Science president Kurt Lambeck praised the quality of the report by Working Group I of the IPCC.

He urged governments and industries to take swift action to reduce the pace of change to give "societies and ecosystems" time to adapt to a warmer and more unstable world. "Climate change is here to stay," said Professor Lambeck. "We must open our eyes to what may be the most significant issue facing not only Australia but the planet."

In Britain, Royal Society president Martin Rees agreed, saying the report was a "comprehensive picture" of the latest scientific understanding of the nature, processes and likely outcomes of climate change. But he correctly predicted a "vocal minority" would raise objections to the findings.

In Melbourne, former head of the weather bureau's National Climate Centre William Kininmonth was among the sceptics. "My feeling is that the report is more alarmist than the evidence suggests," he said.

He was particularly critical of the IPCC's interpretation of the data and of the separate computer modelling systems used to predict future climate changes. He added that, along with Canadian climate-change sceptic Ross McKitrick, he had contributed to an "independent summary for policymakers", to be released in London next Monday.

The current head of the NCC, Michael Coughlan, disputed Mr Kininmonth's objections. He said the latest report built on past work and reflected continuing refinement in the understanding of the complex processes of the climate system. Dr Coughlan said the new report fitted neatly with continuing observations of climate and ocean systems.

"Globally, we're seeing the trends (noted in the report) being laid down now: warming nights and fewer colder days and more heatwaves and heavy precipitation events," he said. "These global trends are consistent with what we've been seeing in Australia over the past 50 to 100 years."

The head of the UN's Environment Program said last night the IPCC report had rendered "almost redundant" a European Union goal of limiting global warming to 2C. Achim Steiner said the new report "gives us a stark warning that the potential impact will be more dramatic, faster and more drastic in terms of consequences" than previously thought.