the combinations of rain-fed versus irrigated agriculture with C3-photosynthetic10 versus C4-photosynthetic plants11. A fifth category involves animal pasturing. These five pathways provide the majority of food consumed by humans.

Rain-fed agriculture is clearly a system at risk in places where climate change brings decreased rainfall and/or increased temperatures during the growing season (and an associated increased demand for water by the plants). Irrigated agriculture may be relatively less vulnerable to the direct consequences of climate change, but the increased use of irrigated water competes with other demands for water. C3 plants are potentially aided by increased atmospheric carbon dioxide (CO2) in terms of an increased photosynthesis rate and increased water-use efficiency; C4 plants do not feature this response (Derner et al., 2003). Grazing systems are vulnerable to water supply for plant productivity and for animal consumption. With climate change, grazing systems can feature catastrophic collapse and can result in longer-term systems degradation.

Agricultural systems are monitored by a variety of technologies including overhead surveillance, which are used in designing production strategies, monitoring irrigation schemes, and assessing the state of crops (DeFries, 2008; NRC, 2008b). Remote-sensing technologies also are significantly applied in commodities prediction (Supit, 1997; Haboudane et al., 2002). Many models are successful at predicting agricultural production for a variety of crops (McCown et al., 1996; Stoorvogel et al., 2004). However, their application to altered climatic conditions is an existing challenge.

Unlike fisheries systems discussed in the next section, mass agricultural production systems are primarily engineered by humans and feature organisms (both plants and animals) that are highly modified genetically through domestication. This coupling of modern agriculture’s technological dependency with the nature of the agricultural species makes the response of agricultural systems to climate change extremely complex to interpret. Additionally the market-driven economic drivers of global commodities markets and agricultural policy restrictions on crop overproduction also complicate the interpretation of vulnerabilities. Food is an essential commodity in world trade, and wealthy nations can buy food when poorer nations cannot.

In early assessments of the potential consequences on agriculture of climate change, it generally was thought that the crop production systems would adjust by using new breeds of crop varieties and/or use crops or varieties of crops from other regions to maintain local and regional agricultural productivity. The remarkable climatic domain within which one can grow a crop such as maize formed some of the basis for these opinions. So did the success of the “Green Revolution” in increasing crop yields in previously marginal situations. However, the metrics in the Land-Surface and Terrestrial Ecosystems Table (Chapter 3) emphasize the monitoring of rain-fed, subsistence agricultural systems, which have less of a technological buffer from climate variation than do advanced technology agricultural systems. Similarly, dry-land grazing systems are also considered. These production systems have the potential to serve as early-

10

All of carbon fixation and photosynthesis happens in mesophyll cells just on the surface of the leaf in C3-photosynthetic plants. These plants are well-adapted to habitats with cool, moist conditions under normal light.

11

Carbon fixation and photosynthesis are split between the mesophyll cells and bundle sheath cells in C4-photosynthetic plants. These plants are well-adapted to habitats with high daytime temperatures and intense sunlight.



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