Bush’s requested climate change review confirms risks from global warming

In a report requested by the Bush administration, 11 of the US' top climate scientists has confirmed the existence of climate change and concludes that much more systematic research is needed to reduce current uncertainties in the science.


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The confirmation in the National Academy of Sciences’ (NAS’) report Climate Change Science: An Analysis of Some Key Questions now leaves President Bush, who previously doubted the existence of global warming and who is due in the coming week to discuss his plans for tackling the phenomenon with the European Union, little room for complacency. The President is likely to have a hard time softening the European stance since he pulled out of the Kyoto Protocol earlier this year and two recent research projects have cast doubt on the effectiveness of his expected strategy of carbon sinks.

“We know that greenhouse gases are accumulating in Earth’s atmosphere, causing surface temperatures to rise,” commented NAS’ committee chair Ralph Cicerone. “We don’t know precisely how much of this rise to date is from human activities, but based on physical principles and highly sophisticated computer models, we expect the warming to continue because of greenhouse gas emissions.”

With regard to the basic question of whether climate change is occurring, the report notes that measurements show that temperatures at the Earth’s surface rose by about one degree Fahrenheit (about 0.6 degrees Celsius) during the 20th century. This warming process has intensified in the past 20 years, accompanied by retreating glaciers, thinning arctic ice, rising sea levels, lengthening of the growing season in many areas, and earlier arrival of migratory birds, the report says.

The committee said the conclusion of the Intergovernmental Panel on Climate Change (IPCC) that the global warming that has occurred in the last 50 years is likely the result of increases in greenhouse gases accurately reflects the current thinking of the scientific community. However, it also cautioned that uncertainties about this conclusion remain because of the level of natural variability inherent in the climate, the questionable ability of models to simulate natural variability on long time scales, and the degree of confidence that can be placed on estimates of temperatures going back thousands of years based on evidence from tree rings or ice cores.

The best information about past climate variability comes from ice cores drilled miles deep in Antarctica and Greenland, which reveal that temperatures changed substantially over the past 400,000 years, with rapid warming occurring over a period of decades, the report says. The ice cores trapped carbon dioxide and methane, showing that the gases were present in the atmosphere at their lowest levels during cold eras and at higher levels during warm eras. Carbon dioxide did not rise much above 280 parts per million by volume (ppmv) until the industrial revolution. By the end of the 20th century, it had reached 370 ppmv, with an average increase in the last two decades of 1.5 ppmv a year. Both carbon dioxide and methane are more abundant in the atmosphere now than at any time during the 400,000-year ice core record, the report states.

However, new research has also shown that impurities trapped in ancient glacial or polar ice can actually migrate considerable distances, providing false data.

The committee also called the IPCC’s range of scenarios concerning future greenhouse gas emissions “valuable” because they provide a warning of the magnitude of climate change that may occur if emission rates continue to climb at a speed similar to the last century, but it also said alternative scenarios are needed to illustrate the sensitivity to underlying assumptions, particularly with regard to future technological development and energy policy.

Looking to the future, the committee suggested that improvements to the IPCC process may need to be made to ensure the best scientific representation possible, and to keep it from being seen as too heavily influenced by governments “which have specific postures with regard to treaties, emissions controls, and other policy instruments”.

To reduce some of the uncertainties inherent in current climate change predictions, a strong commitment must be made to basic research as well as to improving climate models and building a global climate observing system, the committee said. More comprehensive measurements of greenhouse gases and increased computational power also will be needed.

In the same week, new research (see this week’s ‘World’ section) has suggested that global warming could even exceed the IPCC’s maximum expected temperature increases.

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