From Global Warming Art
This image shows some of the primary results of the Climate: Long range Investigation, Mapping, and Prediction (CLIMAP) project undertaken in the 1970s and 80s. Shown is the outline of the continents after a sea level reduction of 130 meters, the positions of continental ice sheets and winter sea ice, and the change in sea surface temperatures across the oceans (CLIMAP 1981). All three of these are depicted as they are believed to have appeared roughly 18 thousand years ago during the last glacial maximum of the present ice age.
The average cooling of oceanic areas not covered with sea ice is 1.75 °C. On the basis of this and the distribution of ice sheets, it is estimated that Earth as a whole cooled 3.0 ± 0.6 °C during the last glacial maximum (Hoffert and Covey 1992). As most of the climate change in the tropics during this time is believed to have been caused by natural changes in greenhouse gases, this estimate provides a constraint on the radiative forcing associated with those gases and helps to calibrate the amount of change that might be expected from global warming. The estimate of three degrees implies a climate sensitivity to carbon dioxide changes at the low end of the range proposed by the Intergovernmental Panel on Climate Change .
The CLIMAP suggestion that the Pacific warmed during the last glacial maximum has been persistently controversial. To date, no climate model has been able to reproduce the proposed warming in the Pacific (Yin and Battisti 2001), with most preferring a several degree cooling. Also, it appears that climate models which are forced to match the CLIMAP sea surface measurements are too warm to match estimates for changes at continental locations (Pinot et al. 1999). These factors suggest that CLIMAP systematically overestimated the temperatures in the tropical oceans though there is at present no consistent explanation for why or how this should have happened. Unfortunately the cost and difficulty of collecting sediment cores from the open Pacific has limited the availability of samples that might help to confirm or disprove these observations. If the Pacific reconstruction is assumed to be in error, it would result in a larger climate sensitivity to changes in greenhouse gases.
CLIMAP sea surface temperature and glacial data is available through the NOAA paleo collection.
The coastal curves appearing in this figure are improved by incorporating NGDC bathymetry data.
This image was prepared by Robert A. Rohde from published data and is part of the Global Warming Art project.
- Hoffert, M.I. and C. Covey (1992). "Deriving global climate sensitivity from paleoclimate reconstructions". Nature 360: 573-576.
- Jeffrey H. Yin and David S. Battisti (2001). "The Importance of Tropical Sea Surface Temperature Patterns in Simulations of Last Glacial Maximum Climate". Journal of Climate 14 (4): 565–581.
- Pinot, S., G. Ramstein, S.P. Harrison, I.C. Prentice, J. Guiot, M. Stute, S. Joussaume and PMIP-participating-groups (1999). "Tropical paleoclimates at the Last Glacial Maximum: comparison of Paleoclimate Modeling Intercomparison Project (PMIP) simulations and paleodata". Climate Dynamics 15: 857-874.
- CLIMAP (1981). Seasonal reconstructions of the Earth’s surface at the last glacial maximum in Map Series, Technical Report MC-36. Boulder, Colorado: Geological Society of America.
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