A comparison of a GCM response to historical anthropogenic land cover change and model sensitivity to uncertainty in present-day land cover representations |
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| Authors: | Johannes Feddema Keith Oleson Gordon Bonan Linda Mearns Warren Washington Gerald Meehl Douglas Nychka |
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| Institution: | (1) Department of Geography, University of Kansas, Lawrence, KS 66045, USA;(2) National Center for Atmospheric Research, Boulder, CO 80305, USA |
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| Abstract: | This study assesses the sensitivity of the fully coupled NCAR-DOE PCM to three different representations of present-day land
cover, based on IPCC SRES land cover information. We conclude that there is significant model sensitivity to current land
cover characterization, with an observed average global temperature range of 0.21 K between the simulations. Much larger contrasts
(up to 5 K) are found on the regional scale; however, these changes are largely offsetting on the global scale. These results
show that significant biases can be introduced when outside data sources are used to conduct anthropogenic land cover change
experiments in GCMs that have been calibrated to their own representation of present-day land cover. We conclude that hybrid
systems that combine the natural vegetation from the native GCM datasets combined with human land cover information from other
sources are best for simulating such impacts. We also performed a prehuman simulation, which had a 0.39 K ~higher average
global temperature and, perhaps of greater importance, temperature changes regionally of about 2 K. In this study, the larger
regional changes coincide with large-scale agricultural areas. The initial cooling from energy balance changes appear to create
feedbacks that intensify mid-latitude circulation features and weaken the summer monsoon circulation over Asia, leading to
further cooling. From these results, we conclude that land cover change plays a significant role in anthropogenically forced
climate change. Because these changes coincide with regions of the highest human population this climate impact could have
a disproportionate impact on human systems. Therefore, it is important that land cover change be included in past and future
climate change simulations. |
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