The summit - called to work out how British agriculture will be hit by climate change - will hear that summer rainfall may drop by more than half in the south and east of the country, causing acute water shortages and seriously damaging farms.
The summit - which will bring the Environment ministers Elliot Morley and Lord Whitty together with top officials from the National Farmers Union, the Tenants Farmers Association and the Country Land and Business Association - will also be told that warmer winters will increase pests and hinder the germination of crops.
But, in compensation, a hotter Britain is likely to be able to grow more of its own wine.
The papers being prepared for the summit say that scorching summers will become more frequent with global warming, with "very hot Augusts" - such as in 1995 - happening once every five years by 2050. Less rain will fall, and more moisture will evaporate from the soil, causing droughts.
They say: "Hotter and drier summers, with a resulting increase in evaporation, are likely to result in a seasonal reduction in available water resources and the increased risk and intensity of drought. The areas currently under most pressure from agriculture will become further stressed as the regional effects of change are felt."
They add that, by 2080, rainfall in southern and eastern England "may decrease by 50 per cent or more" while soil moisture may drop by over 40 per cent over "large parts" of the country.
In winter, Britain will face the opposite problem, as rainfall rises sharply. Rivers will flood with greater frequency so that the Government will no longer "be able to justify maintaining current standards of protection", and farmland in flood plains will be abandoned to the waters. Coastal areas will also flood more frequently from rising seas. Pests will increase without cold winters to kill them off and winter crops will suffer as most of them need cold to "vernalise" them.
By contrast, farmers could reap some short-term benefits from global warming as the growing season lengthens and higher levels of carbon dioxide in the air encourage crops. The papers expect that farmers will also benefit as global warming hits competing countries harder, and forecast that "higher temperatures may make it possible to grow new crops on a larger area".
t Every new car in Britain will display a colour-coded "energy label" to show how costly it is to run in a new drive to combat the growth in gas-guzzling 4x4s and luxury cars.
The scheme will be unveiled on Wednesday by Alistair Darling, the Secretary of State for Transport, in an attempt to persuade car buyers to switch to more fuel-efficient models.
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