Significant climate tipping points have been passed

by David Spratt

While the world's attention was on Bali in December 2007, a remarkable set of comments and predictions were made by Prof. James Hansen, Director of the NASA Goddard Institute of Space Science and other scientists at the annual meeting of the American Geophysical Union on Thursday, 13 December 2007.

Here is a summary of the main points:

• Climate tipping points have been passed. These include large ice sheet disintegration, significant sea level rises and species loss.
• These tipping points were passed when we exceeded 300-350 parts per million of carbon dioxide in the atmosphere, a point passed decades ago.
• The Arctic will soon be ice-free in the summer.
• There is already enough carbon in Earth's atmosphere to lose Arctic sea ice cover and for massive ice sheets such as in Greenland to eventually melt away, and ensure that sea levels will rise several feet (meters) in coming decades.
• Climate zones such as the tropics and temperate regions will continue to shift, and the oceans will become more acidic, endangering much marine life.
• "We have passed that (Greenland) and some other tipping points in the way that I will define them," Hansen said in an email. "We have not passed a point of no return. We can still roll things back in time — but it is going to require a quick turn in direction."
• "We either begin to roll back not only the emissions [of carbon dioxide] but also the absolute amount in the atmosphere, or else we're going to get big impacts." "We should set a target of CO2" that's low enough to avoid the point of no return. The CO2 tipping point for many parts of the climate is around 300 to 350 parts per million, Hansen estimated.
• "We have to figure out how to live without fossil fuels someday," Hansen said. "Why not sooner?
• People must not only cut current carbon emissions but also remove some carbon that has collected in the atmosphere since the Industrial Revolution

Beck, A. Carbon cuts a must to halt warming-US scientists, Reuters, 13 December 2007

Inman, M. Global Warming "Tipping Points" Reached, Scientist Says, National Geographic News, 14 December 2007

Borenstein, S. Arctic Sea Ice Gone in Summer Within Five Years? Associated Press, 12 December 2007

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