Scientific Colloquium
October 22, 2004

                "Human-Induced Climate Change: To Hedge or Not to Hedge Against an Uncertain Climate Future"

Although carbon dioxide (CO2) comprises only 0.03% of the Earth's atmosphere, its projected doubling this century may change the climate significantly.  Recent empirical estimates of climate sensitivity, DT2x – the change in global-mean near-surface temperature due to a doubling of the pre-industrial CO2 concentration – indicate there is a 90% likelihood that 1.0°C ≤ DT2x ≤ 9°C.  Some have argued that little or nothing should be done until such “deep” uncertainty is significantly reduced.  However, a new study finds that hedging in the near term effectively “buys insurance” against future adjustment costs and is extremely robust across most possible futures, especially when compared with a wait-and-see strategy that would eschew mitigation over the first third of this century.