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The general trend of simulation results for coming decades is an increase in crop yields, at least in the northern half of Europe. As an example, a raw application of yield projections to presently suitable areas and yield levels of 1990 for winter wheat in the EU suggests an average increase of 9-11 million tons per year for the years 2013-2036 (IS92 a and d emission scenarios, UKTR3140 and GFDL2534 climate scenarios, equivalent years based on climate sensitivity) and 24-26 million tons per year for the years 2042-2100 (IS92a and d emission scenarios, UKTR6675 and GFDL5564 climate scenarios) (CLAIRE, 1996).
Increasing stress may be associated with a more variable climate (both intra-annual and interannual), with an increase in the probability of rare events. This effect is not obvious at all stages, however (e.g., winter temperature in high latitudes may become less variable where the meridional temperature gradient is reduced). Because European agriculture is highly adapted-that is, prepared to provide large outputs as a response to a restricted range of inputs-it could be severely impacted by more frequent sequences of such extreme events. As Semenov and Porter (1995) state, "Future climatic scenarios derived from GCMs have described changes in mean weather, but nonlinear crop models require explicit incorporation of changes in climatic variability to assess the risks of agricultural production from climate change." Breeding of new cultivars and planting of cultivars in previously less-suitable areas may be successful adaptation options, provided that farmers can distinguish between anomalous weather and climatic trends.
Increasing yields are related chiefly to increasing production of dry matter. Simulations show that only carbon weight is promoted in this dynamic, and the carbon-to-nitrogen ratio increases in dry matter. This effect often is linked with a loss in product quality (for bakeries, breweries, animal feeding, etc.).
A northward change in temperature patterns may not necessarily correspond to a simple shift in latitude of suitable areas for usual crops because many plants are sensitive to photoperiod and adapted to a combination of temperature and photoperiod ranges. New genotypes therefore might be necessary to meet this new agricultural frontier, provided that the available soils are suitable for the crop.
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