There are a number of ways in which changes in land use can influence climate. The most direct influence is through the alteration of Earth’s albedo, or surface reflectance. For example, the replacement of forest by cropland and pasture in the middle latitudes over the past several centuries has led to an increase in albedo, which in turn has led to greater reflection of incoming solar radiation in those regions. This replacement of forest by agriculture has been associated with a change in global average radiative forcing of approximately –0.2 watt per square metre since 1750. In Europe and other major agricultural regions, such land-use conversion began more than 1,000 years ago and has proceeded nearly to completion. For Europe, the negative radiative forcing due to land-use change has probably been substantial, perhaps approaching –5 watts per square metre. The influence of early land use on radiative forcing may help to explain a long period of cooling in Europe that followed a period of relatively mild conditions roughly 1,000 years ago. It is generally believed that the mild temperatures of this “medieval warm period,” which was followed by a long period of cooling, rivaled those of 20th-century Europe.

It improves it, CO2 helps more vegetation grow especially in arid semi desert regions, this means the soil has more roots and soil organisms which helps with it's moisture holding properties, it also helps reduce water run off and wind erosion (dust bowl)

Satellite imaging has shown and increase of up to 14% in vegetation cover since 1980.

That is unknown at this time. Until such time that catastrophic, Man-made, global warming happens.....one can only guess. At least that is what the climate scientists have been saying.

Desertification

http://en.wikipedia.org/wiki/Desertifica...

Makes the ice melt, making water rise, making more floods