The definition of desertification accepted in the ad hoc conference held by UNEP in Nairobi in 1977 and confirmed at the Earth Summit on Environment and Development held in Rio de Janeiro in 1992 is: ?arid, semi-arid and dry-subhumid land degradation?. There is no global long-term trend in any rainfall change over the period of instrumental record (c. 150 years), but there has been an increase of 0�5�C in global temperature over the past 100 years. This increase seems partly due to urbanization, as there is no evidence of it resulting from atmospheric pollution by CO2and other warming gases (SO2, NO2, CH4, CFH etc.). On the other hand, the thermal increase is uneven, increasing with latitudes above 40� N and S. The increase is only [...]
