5.2.1 Current sensitivity
The inter-annual, monthly and daily distribution of climate variables (e.g., temperature, radiation, precipitation, water vapour pressure in the air and wind speed) affects a number of physical, chemical and biological processes that drive the productivity of agricultural, forestry and fisheries systems. The latitudinal distribution of crop, pasture and forest species is a function of the current climatic and atmospheric conditions, as well as of photoperiod (e.g., Leff et al., 2004). Total seasonal precipitation as well as its pattern of variability (Olesen and Bindi, 2002) are both of major importance for agricultural, pastoral and forestry systems.
Crops exhibit threshold responses to their climatic environment, which affect their growth, development and yield (Porter and Semenov, 2005). Yield-damaging climate thresholds that span periods of just a few days for cereals and fruit trees include absolute temperature levels linked to particular developmental stages that condition the formation of reproductive organs, such as seeds and fruits (Wheeler et al., 2000; Wollenweber et al., 2003). This means that yield damage estimates from coupled crop-climate models need to have a temporal resolution of no more than a few days and to include detailed phenology (Porter and Semenov, 2005). Short-term natural extremes, such as storms and floods, interannual and decadal climate variations, as well as large-scale circulation changes, such as the El Niño Southern Oscillation (ENSO), all have important effects on crop, pasture and forest production (Tubiello, 2005). For example, El Niño-like conditions increase the probability of farm incomes falling below their long-term median by 75% across most of Australia's cropping regions, with impacts on gross domestic product (GDP) ranging from 0.75 to 1.6% (O'Meagher, 2005). Recently the winter North Atlantic Oscillation (NAO) has been shown to correlate with the following summer's climate, leading to sunnier and drier weather during wheat grain growth and ripening in the UK and, hence, to better wheat grain quality (Atkinson et al., 2005); but these same conditions reduced summer growth of grasslands through increased drought effects (Kettlewell et al., 2006).
The recent heatwave in Europe (see Box 5.1) and drought in Africa (see Table 5.1) illustrate the potentially large effects of local and/or regional climate variability on crops and livestock.
Multiple stresses, such as limited availability of water resources (see Chapter 3), loss of biodiversity (see Chapter 4), and air pollution (see Box 5.2), are increasing sensitivity to climate change and reducing resilience in the agricultural sector
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