Publication Abstracts

Gornitz 1987

Gornitz, V., 1987: Climatic consequences of anthropogenic vegetation changes from 1880-1980. In Climate: History, Periodicity, and Predictability. M.R. Rampino, J.E. Sanders, W.S. Newman, and L.K. Koenigsson, Eds. Van Nostrand Reinhold, pp. 47-69.

Anthropogenic modification of the land cover can influence climate directly through release of CO2 into the atmosphere, through changes in the surface albedo, and indirectly through disruption of the hydrologic cycle and in generation of wind-blown dust and aerosols. This chapter focuses on the albedo changes associated with land-use alterations from the end of the nineteenth century to the present and the ensuing climatic implications.

The expansion of cultivated land provides one of the few documented records of land-use change, yet estimates of conversion to agriculture since the end of the nineteenth century range between 725 million ha and 931 million ha. Since the 1950s, the global forest area has remained close to 4 billion ha, but poor statistics in older surveys and some temperate-land reforestation mask any anticipated decrease. At present, deforestation affects between 9 million ma and 19 million ha per year (Seller and Crutzen, 1980; Lanly, 1982).

A re-examination by Henderson-Sellers and Gornitz (1984) of Sagan, Toon, and Pollack's (1979) calculation of albedo changes associated with anthropogenic vegetation changes during a 30-yr period showed an increase in albedo of only around half that reported by Sagan and co-workders. These albedo changes would result in a temperature decrease of only 0.06-0.09 K.

Western Africa, as a microcosm of vegetation changes in the tropics, was selected for more detailed study. Land-use changes in western Africa were reconstructed from historical records, censuses, atlases, and descriptive reports. Agricultural and population censuses suggest that since 1930, permanently cultivated land has increased by about 40 million ha (44 million ha extrapolated to 1910). If fallow land is included, up to 115 million ha may have been cleared since 1910. The forest zone in the twentieth century has been reduced by around 60-70%. A conservative estimate suggests removal of up to 123 million ha of forest and woodland.

Albedo changes corresponding to these land-use alterations were calculated. The mean regional albedo increased from 17.3% (natural vegetaion only) to 17.4% in 1880 and 17.8% in 1980, or an increase of 0.4% since the late nineteenth century and 0.5% since agriculture began.

Precipitation shows no apparent secular decrease linked to vegetation clearing, as suggested by some climatic models. However, disruption of the hydrologic cycle as a result of devegetation may have led to reductions in soil moisture, placing plants under stress and simulating a climatic dessication.

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BibTeX Citation

@inbook{go07100z,
  author={Gornitz, V.},
  editor={Rampino, M. R. and Sanders, J. E. and Newman, W. S. and Koenigsson, L. K.},
  title={Climatic consequences of anthropogenic vegetation changes from 1880-1980},
  booktitle={Climate: History, Periodicity, and Predictability},
  year={1987},
  pages={47--69},
  publisher={Van Nostrand Reinhold},
  address={New York, N.Y.},
}

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RIS Citation

TY  - CHAP
ID  - go07100z
AU  - Gornitz, V.
ED  - Rampino, M. R.
ED  - Sanders, J. E.
ED  - Newman, W. S.
ED  - Koenigsson, L. K.
PY  - 1987
TI  - Climatic consequences of anthropogenic vegetation changes from 1880-1980
BT  - Climate: History, Periodicity, and Predictability
SP  - 47
EP  - 69
PB  - Van Nostrand Reinhold
CY  - New York, N.Y.
ER  -

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