Greenhouse-gas feedbacks estimated from Dansgaard-Oeschger events
<p>There are large uncertainties in the estimation of greenhouse-gas feedbacks: model-based estimates vary considerably; recent observations are too short provide strong constraints. Rapid climate changes during the last glacial period (Dansgaard-Oeschger, D-O, events) are potentially valuable because they are comparable in rate and magnitude to projected future climate warming, and are registered near-globally. Here we use D-O events to quantify the centennial-scale feedback strength of feedbacks involving CO<sub>2</sub>, CH<sub>4</sub> and N<sub>2</sub>O. We use climate model simulations of the D-O events to estimate the relationship between global mean and Greenland temperature. We then relate global mean temperature changes to changes in greenhouse-gas concentrations derived from ice-core records, and then estimate the associated radiative forcing. We found the magnitude of the feedbacks (expressed in gain, with 95 % confidence interval) to be 0.07 &#177; 0.02 for CO<sub>2,</sub> 0.04 &#177; 0.01 for CH<sub>4</sub>, 0.04 &#177; 0.01 for N<sub>2</sub>O. These estimates are more constrained than previous model-based estimates but comparable to estimates based on recent observations.</p>