The two major warming phases of the last deglaciation at similar to 14.7 and similar to 11.5 ka cal BP in Europe: climate reconstructions and AGCM experiments

• Published in: Global and Planetary Change
• Main Authors: Renssen, H., Isarin, RFB, Workshop on Rapid Climatic Warming at the End of the Last Glacial - Palaeodata Analysis and Climate Modeling
• Other Authors: UCL - Autre
• Format: Conference Object
• Language: English
• Published: Elsevier Science Bv 2001
• Subjects: Climate Change; General Circulation Model; Simulation; Reconstruction; Europe; Late-glacial; Paleoclimate Maps; Greenland; Sea ice
• Online Access: http://hdl.handle.net/2078.1/61894; https://doi.org/10.1016/S0921-8181(01)00082-0

During the last deglaciation two distinct warming phases occurred in the N Atlantic region at similar to 14.7 and similar to 11.5 ka cal BP. These two shifts are the transitions from (1) GS-2a (Greenland Stadial 2a) to GI-1e (Greenland Interstadial 1e) and (2) GS-1 to the Preboreal. In this study we characterise these two important climate transitions by comparing maps of January and July temperatures for Europe acquired with two independent methods: (1) simulations with the ECHAM4 atmospheric general circulation model in T42 resolution and (2) temperature reconstructions based on geological and palaeoecological data. We also compare estimated lake level changes with simulated P-E (effective precipitation) values. These comparisons enable quantification of the climate change during the two phases. January temperatures increased by as much as 20 degreesC in NW Europe from values between - 25 degreesC and - 15 degreesC in both GS-2a and GS-1 to temperatures between - 5 degreesC and 5 degreesC in both GI-le and the Preboreal. During July the changes were smaller, as the July temperatures increased in NW Europe by 3-5 degreesC from about 10 degreesC to 15 degreesC in both GS-2a and GS-1 to values of 13 degreesC to 17 degreesC in both GI-1e and the Preboreal. In S Europe the increase in July temperature was less intense. Our analysis suggests that the effective precipitation remained at the same level during the 14.7 ka cal BP transition, whereas a small increase is inferred for some regions for the 11.5 ka cal BP shift. This small effect in effective precipitation is explained by comparable increases in precipitation and evaporation during both transitions. We infer that the strong increase in January temperatures was forced by changes in the N Atlantic Ocean, as the variations in sea surface temperatures and the position of the sea ice margin determined the temperature chan-e over land. The increase in July temperatures was mainly driven by two factors: the increase in insolation and the deglaciation in Scotland ...