Paleoclimatic Perspectives on Climate Sensitivity to Carbon Dioxide
Abstract
This research investigates the Earth's climatic history for insight into the potential values of climate sensitivity to carbon dioxide. The goal is to contribute to current scientific and policy debates regarding uncertainties in climate change predictions. Temperature and carbon dioxide records are compared over four time resolutions: Phanerozoic, Cenozoic, late Quaternary, and the rapid change of glacial terminations. Analytical and statistical methods are developed to directly include several sources of uncertainty in estimates of sensitivity and to analyze continuous change rather than just maximum to minimum ranges. The results agree with other recent analyses of paleoclimatic records that find sensitivity values previously have been underestimated. However, the extent of coverage and improved statistical methods of this paper enable a more robust analysis. The Phanerozoic records are available at a resolution insufficient to undergo such a quantitative analysis, but the new methodological improvements of this research do have implications for previously published estimates. The Cenozoic similarly is limited by sparse data availability and high calibration uncertainties, but bottom water records produce estimates of sensitivity values that range over 1-5 (± 3) K. Analyses of the late Quaternary utilize a large sample size of ocean temperature records distributed globally and ice core carbon dioxide records. The calculated sensitivity values are 5 ± 1.5 K for the tropics, 4.5 ± 2 K for bottom water, 15 ± 3 K for polar ice sheets, and an estimated global sensitivity of 6.5 ± 1.5 K. Such means are on the outer edge of the range of sensitivity values most commonly considered by climate models. Analyses of periods of rapid climate change during glacial terminations do not find significant changes in climate sensitivity during such periods, nor do comparisons of interglacial with glacial periods find significant changes in the above estimates. However, the calculated estimates remain limited by a need for further inclusion of ice-sheet forcing into the analysis.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFMGC22A..05S
- Keywords:
-
- 1600 GLOBAL CHANGE;
- 4930 Greenhouse gases;
- 4954 Sea surface temperature