IPCC Special Report on Emissions Scenarios

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3.5.7. Conclusions

Some of the main findings regarding different categories of land-use emissions are outline below.

Global scenarios of CO2 emissions from deforestation have their widest range around the middle of the 21st century and converge on zero toward the end of the century. The eventual decrease in emissions computed by the scenarios results in part from the assumed slowing of agricultural land expansion in tropical regions. Another reason is some scenarios assume that forests will nearly disappear in Asia and Africa before or around the middle of the 21st century.

Most global scenarios of CH4 emissions from rice cultivation show an upward trend until the middle of the 21st century and then stabilize. The global trend is chiefly influenced by estimates for Asia, where more than 80% of these emissions currently originate. Normalized global emissions range by a factor of three in the year 2100. The wide range has mostly to do with different estimates of the future rice cropland area, which is influenced largely by different assumptions about future rice productivity.

All global scenarios of CH4 emissions from enteric fermentation show an upward trend until the end of the 21st century. The maximum range of normalized emissions is by a factor of 2.0 (which occurs in the year 2100), the smallest range of the four categories of emissions examined. Also, these emissions have the smallest range of current estimates in the literature, and the smallest range of base-year estimates in the scenarios. Most scenarios of emissions in industrial regions show a stabilizing or decreasing trend, because of the assumption that the number of livestock will continue to decline with decreasing demand for beef and increasing animal productivity. Meanwhile, the assumed economic development in the developing regions will stimulate demand for beef, which leads to an increase in livestock (despite improvements in animal productivity) and higher emissions.

Most global scenarios show that N2O emissions from fertilized soils continue to increase up to the end of the 21st century, and the range of estimates of normalized emissions in 2100 exceeds a factor of two.

Three of the four categories of emissions show increasing global trends up to the end of the 21st century. The exception is CO2 from deforestation (see above). Hence it is likely that land-use emissions will continue to contribute significantly to the build-up of GHGs in the atmosphere, especially to levels of CH4 and N2O. Studies of mitigation of climate change should take this into account and scenarios of land-use emissions should be included in these studies.

Regarding regional scenarios, land-use emissions stabilize or decrease in industrial regions, and increase substantially in Africa, but less so in Asia. Emission trends in Latin America are between those of industrial and developing regions. These regional trends reflect the stabilizing demand for agricultural products and agricultural land in industrial countries, and the assumed continuation of agricultural development elsewhere.

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