Climate Change and Agriculture

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The future of humankind depends upon, among other factors, our continued ability to feed ourselves. The specter of suffering, breakdown of social order, and the chaos that would result if this ability were ever seriously called into question on a global scale surpasses our ability to comprehend fully. Future global food security will be influenced by three major, interrelated pressures: (a) population growth, (b) rising cost of energy, and (d) disruption of the global climate system. Simply put, more people, using more energy, are changing the global climate at a rate that may exceed our ability to adapt our agricultural systems, and this calls into question the unthinkable: Can we, and, if so, for how long, continue to feed the world's population?

Far from being a passive sector, agriculture is a major contributor to global climate change. Agricultural expansion is the primary driver of deforestation and land cover change worldwide, accounting for between 17-24% of the total CO2 emissions (IPCC 2007c; US/EPA 2006b; see Table 23.1). When combined with the direct and indirect emissions from production agriculture (e.g., methane, nitrous oxide), the agricultural sector is responsible for roughly one-third of the total anthropogenic emissions, and even more if the share of food industry energy consumption and transportation are included (IPCC 2007b; US/EPA 2006b).

The rising costs of fossil fuels (the current dip in prices notwithstanding) needed to irrigate more land, produce more fertilizer, and move more food around the globe will add further pressure to an already charged situation. These costs are beginning to influence decisions about the allocation of land

Table 23.1 Agricultural sources of greenhouse gas emissions in 2000 (after IPCC 2007c; US/EPA 2006b) measured in mega tonnes CO2 equivalent.

Sources Mt CO2e

Land conversion 5900

Nitrous oxide from soils 2128

Methane from cattle enteric fermentation 1792

Biomass burning 672

Rice production (methane) 616

Manure 413

Fertilizer production 410

Irrigation 369

Farm machinery 158

Pesticide production 72

and water resources for biofuel feedstock production, both to replace fossil fuels and to mitigate a portion of the growing GHG emissions. Any further expansion in the agricultural footprint to support biofuel production will invariably lead to increased CO2 emissions through land use change, which in turn will exacerbate climate change impacts.

Recent studies have looked at the carbon footprint of biofuel production when land use change is taken into consideration (Fargione et al. 2008). These studies suggest that if land is converted from export agriculture to domestic biofuel feedstocks, land conversion in other world regions for export agriculture can result in carbon emissions. Thus, when corn in North America is redirected to ethanol production, there will be increased demands to convert land in other world regions to produce cereals for export. Often, these converted lands are high carbon tropical forests, which if transformed results in GHG emissions. The additional sources of greenhouse gases from land conversion significantly extends the payback period for biofuel substitution (Table 23.2).

In addition to land, the other critical natural resource that is coming under increased pressure is freshwater. Agriculture currently accounts for over 70% of global freshwater use; 85% of this occurs in developing countries (World Bank 2008). Assumptions behind future increases in productivity—be it the extension of agriculture into more marginal lands, agriculture intensification or adaptive measures to compensate for rising temperatures, or changes in local precipitation patterns—all rely to some extent on increased use of water resources, especially irrigation.

The impacts of climate change on agriculture are already visible. Global temperatures have increased by 0.7°C over the past 40 years (2-4°C in high latitudes), leading to yield declines in the tropics and the potential for increased production in the northern latitudes. Sea levels have risen by 20 cm over the past century and will continue to rise more rapidly in the future, threatening coastal areas. The warming of sea surface temperatures has probably led to an

Table 23.2 Payback period for biofuels (Fargione et al. 2008).

Original ecosystem

Location

Biofuel type

Payback period (years)

Peatland rainforest

Malaysia

Palm biodiesel

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