is estimated that man-made changes in land-use have, until now,
produced a cumulative global loss of carbon from the land of about
200 thousand million tonnes. Widespread deforestation has been the
main source of this loss, estimated to be responsible for nearly
90 percent of losses since the mid-nineteenth century. Losses primarily
occur due to the relatively long term carbon sinks of forests being
replaced by agricultural land.
The conversion of land from forested to agricultural
land can have a wide range of negative effects as far as greenhouse
gas emission is concerned. Soil disturbance and increased rates
of decomposition in converted soils can both lead to emission of
carbon to the atmosphere, with increased soil erosion and leaching
of soil nutrients further reducing the potential for the area to
act as a sink for carbon.
Man's need for wood, for fuel and construction, and our ever increasing
need for agricultural land has led to systematic clearances of forests
across the planet in the last few hundred years. Today the pressure
on forested areas is huge, with a rapidly growing human population
requiring food and the land necessary for its growth.
Potential for control
Land-use change is driven by a host of social, political and economic
factors around the world. Increased awareness of the most sensitive
way to manage land and the better agricultural practice, combined
with political agreement on food trade and avoidance of deforestation,
are required if land-use change is not to continue being a net global
source of carbon to the atmosphere in years to come. Indeed, having
degraded large areas of the terrestrial carbon sink, sensitive land-use
change may in fact provide a sink for atmospheric greenhouse gases
in the future.