Figure 5-5: The recent
net uptake of carbon on the land is partly due to enhanced CO2 uptake
through plant growth, with a delay before this carbon is returned to the atmosphere
via the decay of plant material and soil organic matter. Several processes
contribute to the enhanced plant growth: changes in land use and management, fertilizing
effects of elevated CO2 and nitrogen, and some climate changes (such
as a longer growing season at high latitudes). A range of models (identified by
their acronyms in the figure) project a continued increase in the strength of
the net carbon uptake on land for several decades, then a leveling off or decline
late in the 21st century for reasons explained in the text. The model results
illustrated here arise from the IS92a scenario, but similar conclusions are reached
using other scenarios.
