Tipping Point?

In February 2005, climate scientists met in Exeter, UK, for "Avoiding Dangerous Climate Change," an international symposium on the stabilization of greenhouse gas concentrations. The conference steering committee's report, published a year later, focuses on the issue of "tipping points" or critical thresholds. Based on a survey of existing literature, the committee predicts "increasing damage if the globe warms about 1 to 3 C above current levels. Serious risk of large scale, irreversible system disruption, such as reversal of the land carbon sink and possible destabilisation of the Antarctic ice sheets is more likely above 3 C" (5). The committee then suggests 2 C as a threshold beyond which the risk of catastrophic ecosystems failure would become unacceptably high, stating that to limit "warming to 2 C above pre-industrial levels with a relatively high certainty requires the equivalent concentration of CO2 to stay below 400 ppm" (6). The equivalent concentration of CO2 is calculated by adding together the effects of carbon dioxide, methane, and nitrous oxide.

When the conference report was released, The Independent commissioned Keith Shine, head of the meteorology department at the University of Reading, to calculate the equivalent concentration of CO2 in the atmosphere. A widely read article, published on February 11, 2006 under the title, "Global Warming: Passing the 'Tipping Point,'" reported the resulting figure of 425 ppm. The article quotes veteran environmentalist Tom Burke, who argues that "we have actually entered a new era--the era of dangerous climate change.... Governments must stop talking and start spending. We already have the technology to allow us to meet our growing need for energy while keeping a stable climate. Doing so will cost less than the Iraq war, so we know we can do it."