5.1.1 Importance of agriculture, forestry and fisheries
At present, 40% of the Earth's land surface is managed for cropland and pasture (Foley et al., 2005). Natural forests cover another 30% (3.9 billion ha) of the land surface with just 5% of the natural forest area (FAO, 2000) providing 35% of global roundwood. In developing countries, nearly 70% of people live in rural areas where agriculture is the largest supporter of livelihoods. Growth in agricultural incomes in developing countries fuels the demand for non-basic goods and services fundamental to human development. The United Nations Food and Agriculture Organization (FAO) estimates that the livelihoods of roughly 450 million of the world's poorest people are entirely dependent on managed ecosystem services. Fish provide more than 2.6 billion people with at least 20% of their average per capita animal protein intake, but three-quarters of global fisheries are currently fully exploited, overexploited or depleted (FAO, 2004c).
5.1.2 Scope of the chapter and treatment of uncertainty
The scope of this chapter, with a focus on food crops, pastures and livestock, industrial crops and biofuels, forestry (commercial forests), aquaculture and fisheries, and smallholder and subsistence agriculturalists and artisanal fishers, is to:
• examine current climate sensitivities/vulnerabilities;
• consider future trends in climate, global and regional food security, forestry and fisheries production;
• review key future impacts of climate change in food crops, pasture and livestock production, industrial crops and biofuels, forestry, fisheries, and small-holder and subsistence agriculture;
• assess the effectiveness of adaptation in offsetting damages and identify adaptation options, including planned adaptation to climate change;
• examine the social and economic costs of climate change in those sectors; and,
• explore the implications of responding to climate change for sustainable development.
We strive for consistent treatment of uncertainty in this chapter. Traceable accounts of final judgements of uncertainty in the findings and conclusions are, where possible, maintained. These accounts explicitly state sources of uncertainty in the methods used by the studies that comprise the assessment. At the end of the chapter, we summarise those findings and conclusions and provide a final judgement of their uncertainties.
5.1.3 Important findings of the Third Assessment Report
The key findings of the 2001 Third Assessment Report (TAR; IPCC, 2001) with respect to food, fibre, forestry and fisheries are an important benchmark for this chapter. In reduced form, they are:
• CO2 effects increase with temperature, but decrease once optimal temperatures are exceeded for a range of processes, especially plant water use. The CO2 effect may be relatively greater (compared to that for irrigated crops) for crops under moisture stress.
• Modelling studies suggest crop yield losses with minimal warming in the tropics.
• Mid- to high-latitude crops benefit from a small amount of warming (about +2°C) but plant health declines with additional warming.
• Countries with greater wealth and natural resource endowments adapt more efficiently than those with less.
• Free-air CO2 enrichment (FACE) experiments suggest that trees rapidly become acclimated to increased CO2 levels.
• The largest impacts of climate change are likely to occur earliest in boreal forests.
• Contrary to the findings of the Second Assessment Report (SAR), climate change will increase global timber supply and enhance existing market trends of rising market share in developing countries.
Aquaculture and fisheries
• Global warming will confound the impact of natural variation on fishing activity and complicate management.
• The sustainability of the fishing industries of many countries will depend on increasing flexibility in bilateral and multilateral fishing agreements, coupled with international stock assessments and management plans.
• Increases in seawater temperature have been associated with increases in diseases and algal blooms in the aquaculture industry.
Research on the consequences of climate change on agriculture, forestry and fisheries is addressing deepening levels of system complexity that require a new suite of methodologies to cope with the added uncertainty that accompanies the addition of new, often non-linear, process knowledge. The added realism of experiments (e.g., FACE) and the translation of experimental results to process crop-simulation models are adding confidence to model estimates. Integrated physiological and economic models (e.g., Fischer et al., 2005a) allow holistic simulation of climate change effects on agricultural productivity, input and output prices, and risk of hunger in specific regions, although these simulations rely on a small set of component models. The application of meta-analysis to agriculture, forestry and fisheries in order to identify trends and consistent findings across large numbers of studies has revealed important new information since the TAR, especially on the direct effects of atmospheric CO2 on crop and forest productivity (e.g., Ainsworth and Long, 2005) and fisheries (Allison et al., 2005). The complexity of processes that determine adaptive capacity dictates an increasing regional focus to studies in order best to understand and predict adaptive processes (Kates and Wilbanks, 2003): hence the rise in numbers of regional-scale studies. This increases the need for more robust methods to scale local findings to larger regions, such as the use of multi-level modelling (Easterling and Polsky, 2004). Further complexity is contributed by the growing number of scenarios of future climate and society that drive inputs to the models (Nakicenovic and Swart, 2000).
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