Coupled atmosphere-ocean-vegetation simulations for modern and mid-Holocene climates: role of extratropical vegetation cover feedbacks |
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| Authors: | Robert Gallimore Robert Jacob John Kutzbach |
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| Institution: | (1) Center for Climatic Research, University of Wisconsin, Madison, 1225 W. Dayton Street, Madison, WI 53706, USA;(2) Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, USA |
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| Abstract: | A full global atmosphere-ocean-land vegetation model is used to examine the coupled climate/vegetation changes in the extratropics
between modern and mid-Holocene (6,000 year BP) times and to assess the feedback of vegetation cover changes on the climate
response. The model produces a relatively realistic natural vegetation cover and a climate sensitivity comparable to that
realized in previous studies. The simulated mid-Holocene climate led to an expansion of boreal forest cover into polar tundra
areas (mainly due to increased summer/fall warmth) and an expansion of middle latitude grass cover (due to a combination of
enhanced temperature seasonality with cold winters and interior drying of the continents). The simulated poleward expansion
of boreal forest and middle latitude expansion of grass cover are consistent with previous modeling studies. The feedback
effect of expanding boreal forest in polar latitudes induced a significant spring warming and reduced snow cover that partially
countered the response produced by the orbitally induced changes in radiative forcing. The expansion of grass cover in middle
latitudes worked to reinforce the orbital forcing by contributing a spring cooling, enhanced snow cover, and a delayed soil
water input by snow melt. Locally, summer rains tended to increase (decrease) in areas with greatest tree cover increases
(decreases); however, for the broad-scale polar and middle latitude domains the climate responses produced by the changes
in vegetation are relatively much smaller in summer/fall than found in previous studies. This study highlights the need to
develop a more comprehensive strategy for investigating vegetation feedbacks. |
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