Wide differences on greenhouse gas effects

The Kyoto protocol, which aims to reduce greenhouse gas emissions by 5 percent between 2008 and 2012, would have little effect on climate change unless far more drastic measures are taken, according to Klaus Hasselmann and colleagues.

Emissions reductions of as much as 50 percent – a goal that Hasselmann says is unattainable with current technology – would still lead to doubling the rate of emissions over the next 500 years. More drastic reductions to achieve near-zero emissions within a century or two are needed.

The International Panel on Climate Change projects a mean global temperature increase due to global warming of somewhere in the range of 1.4 to 5.8 degrees Celsius, compared to a natural variation of 1 to 2 degrees Celsius in average global temperatures over the past 10,000 years.

If all currently known fossil fuels are burned, some scientists predict an average global temperature increase somewhere in the range of 4 to 9 degrees Celsius – in the second half of this millennium; however, such predictions aren't supported by current climate models – they are too far into the future.

Some scientists say sea levels may rise 3 to 8 metres over the next 1,000 years, a claim that computer models do not support.

Interestingly, recent research indicates that coral islands (atolls), now visible in the Pacific, were underwater 2,000 to 4,000 years ago, and that sea levels have fallen 2 metres since then. Thus a rise in sea levels of 2 meters is within the natural variation during historic times. On a longer timescale, 15,000 years ago sea levels were 125 meters below present levels, at the end of the last Ice Age.

Sources: K. Hasselmann et al., The Challenge of Long-Term Climate Change, Science, December 12, 2003; Richard A. Kerr, Pacific Migration Arrested by Meltdown's High Waters, Science, December 12, 2003.

For text (subscription required) http://www.sciencemag.org

For more on Global Warming Science http://eteam.ncpa.org/policy/Global_Warming/Science/

For more on Global Warming Economics http://eteam.ncpa.org/policy/Global_Warming/Economics/

FMF Policy Bulletin\13 January 2004