More than 200 scientists, government officials, and members of civil society gathered in Exeter, United Kingdom (UK) in February 2005 to discuss what constitutes -- and how we can avoid -- dangerous climate change. Among the noteworthy papers presented at the conference, one explored the risks of exceeding a 2 degrees Celsius equilibrium temperature target. The author of this paper concluded that delay in action by as few as 5 to 10 years will increase the probability of exceeding the threshold dramatically.

• Meinshausen, Malte. "On the Risk of Overshooting 2°C." Proceedings from International Symposium on Stabilisation of Greenhouse Gas Concentrations -- Avoiding Dangerous Climate Change, Exeter, 1-3 February 2005 at www.stabilisation2005.com/programme.html.

Meinshausen assigns a probability of exceeding the 2 degrees Celsius threshold a risk of between 68% and 99% at 550 parts per million (ppm) CO2 equivalence levels. However, he suggests that the risks of exceeding the threshold are reduced at lower stabilization levels. For example, at levels of 400 ppm CO2 equivalence, the risks are significantly reduced (to 20% or less).

Implications: According to the IPCC 2001 report, impacts associated with climate increase markedly when global temperatures rise 2 degrees C or more above today's levels. This suggests that aggressive action will be needed: current concentrations are more than 380 ppm and rising about 2 ppm per year. Unfortunately, global policy is not now on course to limit concentrations to below 400 ppm, the level judged "safe" in this analysis.