Human contribution to climate warming

The costs of inaction in mitigating greenhouse gas emissions -- mostly released by burning fossil fuels in power plants, factories and cars -- have became more apparent following the release of a report by the IPCC (Intergovernmental Panel on Climate Change) available at their website here. According to the Washington Post, the report states that Arctic Sea ice will melt by 2100 and that greenhouse gasses are more likely than not making tropical storms more intense. Rising sea levels between 7 and 21 inches will flood low lying areas. The report predicts a rise in temperatures between 3.2 and 7.9 degrees Fahrenheit (1.8 and 4.0 Celsius) in the 21st century. The report notes that the ten hottest years since records began in the 1850’s have occurred since 1994.

According to Achim Steiner , the executive director of the United Nations Environment Program, “The implications of global warming over the coming decades for our industrial economy, water supplies, agriculture, biological diversity and even geopolitics are massive.”

This is particularly important for citizens of the United States, China and India to hear. All three are major polluters and are not participants in the Kyoto Treaty. Under the Kyoto agreement, 35 industrial nations have agreed to cut greenhouse gas emission to 5 percent below 1990 levels by 2012.

This from the BBC:

"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.

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.

The agency said that it would use stronger language to assess humanity's influence on climatic change than it had previously done.

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.

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.

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.

In 2001, using different methodology, the numbers were 1.4 (2.5F) and 5.8C (10.4F).

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.

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 Framework Convention on Climate Change (UNFCCC), said the findings marked a historical landmark in the debate about whether humans were affecting the state of the atmosphere.

"It is an unequivocal series of evidence [showing that] fossil fuel burning and land use change are affecting the climate on our planet."

Mr Steiner, whose agency oversees the operation of the Kyoto Treaty, 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.

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.

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.

The paper compared the 2001 projections on temperature and sea level change report with what has actually happened.

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.

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 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.