Simulating the Holocene climate evolution at northern high latitudes using a coupled atmosphere-sea ice-ocean-vegetation

• Main Authors: Hans Renssen, Æ Hugues Goosse, Æ Thierry Fichefet, Victor Brovkin, Æ Emmanuelle Driesschaert, Æ Frank Wolk
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Arctic; albedo; Labrador Sea; Nordic Seas; Sea ice; taiga; Tundra
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.695.350; http://www.environmental-expert.com/Files%5C6063%5Carticles%5C4932%5CLWJDJCFP68GT98CE.pdf

Abstract The response of the climate at high northern latitudes to slowly changing external forcings was stud-ied in a 9,000-year long simulation with the coupled atmosphere-sea ice-ocean-vegetation model ECBilt-CLIO-VECODE. Only long-term changes in insolation and atmospheric CO2and CH4 content were prescribed. The experiment reveals an early optimum (9–8 kyr BP) in most regions, followed by a 1–3C decrease in mean annual temperatures, a reduction in summer precipita-tion and an expansion of sea-ice cover. These results are in general agreement with proxy data. Over the conti-nents, the timing of the largest temperature response in summer coincides with the maximum insolation differ-ence, while over the oceans, the maximum response is delayed by a few months due to the thermal inertia of the oceans, placing the strongest cooling in the winter half year. Sea ice is involved in two positive feedbacks (ice-albedo and sea-ice insulation) that lead regionally to an amplification of the thermal response in our model (7C cooling in Canadian Arctic). In some areas, the tundra-taiga feedback results in intensified cooling dur-ing summer, most notably in northern North America. The simulated sea-ice expansion leads in the Nordic Seas to less deep convection and local weakening of the overturning circulation, producing a maximum winter temperature reduction of 7C. The enhanced interaction between sea ice and deep convection is accompanied by increasing interannual variability, including two marked decadal-scale cooling events. Deep convection intensifies in the Labrador Sea, keeping the overall strength of the thermohaline circulation stable throughout the experi-ment. 1