30.1 Issues 732

30.1.1 Climate Change and Net Primary Production 733 Climate Change: CO2 Fertilization Impacts on Terrestrial Ecosystem Production 733 Climate Change Impacts on

Forest Ecosystems 733 Climate Change Impacts on

Water Supply 734

30.1.2 Global Warming and Food Insecurity 734 Greenhouse Gases and Food

Security in Low-Income

Countries 734 Effect of Global Climate Change on Agricultural Pests 734 Impact of Climate Change on Agricultural Production in Different Regions 735 Modeling Future Climate Changes and Crop Production Scenario Challenges 735 Policy Considerations Related to Twin Problems of Global

Warming and Food Insecurity 736

30.1.3 Terrestrial Carbon Sequestration and

Food Security 736 Environmental and Socioeconomic Context for Soil Carbon Sequestration 737 Land Use, Soil Management, and

Soil Carbon Sequestration 737 Modeling and Extrapolating Soil Carbon Sequestration 738 Environmental and Socioeconomic Analysis of Soil Carbon Sequestration 738

30.1.4 Policy and Economic Issues 739 Policies and Incentives for Permanent Adoption of Agricultural Carbon Sequestration Practices in Industrialized and Developing Countries 739 Climate Change, Poverty, and Resource-Friendly Agriculture 740 Climate Change and Public

Policy Challenges 741 Climate Change Impacts on Developing Countries 741 Climate Change and Tropical Agriculture: Implications for Social Vulnerability and

Food Security 742

30.2 Identification of Researchable Priorities



742 744 744

The globe has experienced a 31% increase in the atmospheric concentration of carbon dioxide (CO2) and substantial increases in other greenhouse gases (GHGs) since the industrial revolution (Intergovernmental Panel on Climate Change [IPCC], 2001). The current rate of increase of CO2 is about 0.5% or 1.5 ppm per annum. At this rate, the concentration of atmospheric CO2 will double by the end of the 21st century. Environmental and related agricultural impacts of this increased concentration of CO2 and other GHGs are subject to debate. But most would concur that several impacts will result, namely:

• A rise in the mean global temperature, which will cause alterations in the amount and distribution of precipitation, and local, regional, and global changes in water and energy balances

• A fertilization effect of increased atmospheric CO2 on plant growth, with probable increases in biological productivity and water-use efficiency

• A decrease in soil organic carbon (SOC) pools, accompanied by a decline in soil quality and an increase in soil erosion and other degradation processes

• An increase in the incidence of pests and pathogens with attendant adverse effects on crop yields and food production

• Adverse effects on global food security, especially in tropical and subtropical regions that are characterized by soils prone to degradation, large numbers of resource-poor farmers, and high demographic pressures

Climate shifts have occurred almost constantly during the Earth's history. However, the rate of projected change during the 21st century may be unprecedented. Interacting factors involved in this process are complex. However, it is important to assess whether global agricultural production will increase or decrease, whether the quality of soil and water resources will improve or decline, whether the beneficial effects of CO2 fertilization will be enhanced or nullified by other adverse impacts of global warming such as decline in soil quality, and whether food security will be jeopardized in regions with fragile soils and high population density.

Anthropogenic activities, especially land use change and conversion of natural to agricultural ecosystems, have contributed to enrichment of GHGs in the atmosphere since the dawn of civilization (Ruddiman, 2003). Land use conversion and agricultural activities also adversely impacted soil quality. Further, the atmospheric concentration of GHGs is also closely related to soil quality. A decline in soil quality, which results from accelerated erosion and the reduced soil fertility associated with subsistence farming, contributes to the release of CO2 and other GHGs into the atmosphere. Since 1850, global terrestrial ecosystems have released 136 ± 55 Pg (billion metric tons) of C, while fossil fuel emissions have contributed 270 ± 30 Pg (IPCC, 2000). Regarding emissions from terrestrial ecosystems, reductions in the SOC pool represent 78 ±12 Pg (Lal, 1999). The conversion of natural ecosystems to agricultural ecosystems may have depleted as much as 30% to 50% of the SOC pools in the soils of temperate regions and 50% to 75% of those in the tropics (Paul et al., 1997; Lal, 1999, 2000). Depletion of the SOC pool is exacerbated by erosion and soil degradation. Degraded soils in Sub-Saharan Africa and elsewhere in developing countries have low SOC pools because of nutrient mining and accelerated erosion. Enhancement of SOC pools through soil restoration would reverse degradation trends, improve soil quality, increase agronomic/biomass productivity, and mitigate climate change.

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