摘要 : Important findings on the consequences of climate change for agriculture and forestry from the recently completed Third Assessment Report (TAR) of the Intergovernmental Panel on Climate Change (IPCC) are reviewed, with emphasis on... 展开 Important findings on the consequences of climate change for agriculture and forestry from the recently completed Third Assessment Report (TAR) of the Intergovernmental Panel on Climate Change (IPCC) are reviewed, with emphasis on new knowledge that emerged since the Second Assessment Report (SAR). The State-Pressure-Response-Adaptation model is used to organize the review. The major findings are: * Constant or declining food prices are expected for at least the next 25 yr, although food security problems will persist in many developing countries facing population increases, political crisis, poor resource endowments, and steady environmental degradation. Most economic model projections suggest that low relative food prices will extend beyond the next 25 yr. * Although deforestation rates may have decreased since the early 1990s, degradation with a loss of forest productivity and biomass has occurred at large spatial scales as a result of fragmentation, non-sustainable practices and infrastructure development. * According to UN estimates, approximately 23% of all forest and agricultural lands were classified as degraded over the period since 1945. * At a worldwide scale, global change pressures (changes in climate, land-use practices and atmospheric chemistry) are increasingly affecting the supply of goods and services from forests. * The most realistic experiments to date (free air experiments in an irrigated environment) indicate that C3 agricultural crops in particular respond favorably to gradually increasing atmospheric CO2 concentrations, although extrapolation of experimental results to real world production where several factors (e.g., nutrients, temperature, precipitation) are likely to be limiting at one time or another remains problematic. Moreover, little is known of crop response to elevated CO2 in the tropics, as most of the research has been conducted in the mid-latitudes. * Research suggests that for some crops, for example rice, CO2 benefits may decline quickly as temperatures warm beyond optimum photosynthetic levels. However, crop plant growth may benefit relatively more from CO2 enrichment in drought conditions than in wet conditions. * The unambiguous separation of the relative influences of elevated ambient CO2 levels, climate change responses, and direct human influences (e.g. land-use change) on trees at the global and regional scales is still problematic. In some regions such as the temperate and boreal forests, climate change impacts, direct human interventions (including nitrogen-bearing pollution), and the legacy of past human activities appear to be more significant than CO2 fertilization effects. This is an area of continuing scientific debate, although there does appear to be consensus that any CO2 fertilization effect will saturate in the coming century. * Modelling studies suggest that any warming above current temperatures will diminish crop yields in the tropics while up to 2-3 degrees C of warming in the mid-latitudes may be tolerated by crops, especially if accompanied by increasing precipitation. Most developing countries lie in or near the tropics which does not bode well for food production in those countries. * Where direct human pressures do not mask them, there is increasing evidence of the impacts of climate change on forests associated with changes in natural disturbance regimes, growing season length, and local climatic extremes. * Recent advances in modelling of vegetation response suggest that transient effects associated with dynamically responding ecosystems to climate change will increasingly dominate over the next century and that during these changes the global forest resource is likely to be adversely affected. * The ability of livestock producers to adapt their herds to the physiological stress of climate change appears encouraging due to a variety of techniques for dealing with climate stress, but this issue is not well constrained, in part because of the general lack of 收起