Climate Model Tests of the Anthropogenic Influence on Greenhouse-induced Climate Change: the Role of Early Human Agriculture, Industrialization, and Vegetation Feedbacks

• Main Authors: S. Vavrus, W. F. Ruddiman, J. E. Kutzbach
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Arctic; albedo; Climate change; polar desert; Sea ice; Tundra
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.470.9761; http://ccr.aos.wisc.edu/resources/publications/pdfs/CCR_963.pdf

We test the early anthropogenic hypothesis that greenhouse gas emissions produced by early agricultural activities in recent millennia kept the climate warmer than its natural level and offset an incipient glaciation. We use versions of the NCAR’s Community Climate System Model to investigate the natural climate that might exist today if CO2 and CH4 concentrations had fallen to their average levels reached during previous interglaciations (while ignoring the effects of aerosol changes). The model is run in a coupled atmosphere-slab ocean configuration with fixed land cover in one experiment and interactive vegetation changes in the other. With lowered greenhouse gas concentrations, global mean temperature falls by 2.75 K under fixed land cover and by 3.0 K with vegetation feedbacks included. Of the total global cooling with fixed land cover, 38 % (62%) is attributable to early agricultural activities (industrialization), while early agriculture accounts for approximately half of the expanded permanent snow cover area. The large-scale cooling is amplified in polar regions, where mean-annual temperatures fall by up to 9 K and sea ice area more than doubles in the Southern Hemisphere. In high latitudes, boreal forest is replaced by tundra and tundra by polar desert, causing a higher surface albedo that amplifies regional Arctic cooling by up to 2 K annually and 5 K during spring. The greenhouse