Spain will be arid, with all of its agricultural land degraded. India will face a near-tripling of its flood risk. Virtually the whole population of Egypt will be hit by water shortages.
But British farmers will find their crops much easier to grow while their French counterparts will find it harder.
Such will be the varying fortunes of countries by the end of the century if climate change is not brought under control, according to a study by the British Met Office's Hadley Centre for Climate Prediction and Research launched yesterday at the United Nations Climate Conference in Durban.
It is the first detailed, large-scale comparison, using the same methodology. It compares how 24 nations will be affected by the year 2100 if greenhouse-gas emissions continue to pour into the atmosphere unchecked.
In the report's worst-case scenario, food production could decline dramatically in parts of Brazil, China, Egypt, India, Russia, Turkey and the United States. Increases in crop yields could be expected in Japan, Germany and other northern latitudes.
The report applies consistent data to all 24 countries for the first time.
The new analysis suggests climate change could be worse than previously thought in many developing countries. By the end of the century, it says, about 49 million more people, mostly in Bangladesh, China, India and Egypt, could be at risk from coastal flooding from sea level rises.
"Life for millions of people could change forever. This makes the challenge of reducing emissions ever more urgent," said Britain's Climate and Energy Secretary, Chris Huhne.
The researchers used amalgamated results of 21 different computer models of the global climate from institutes around the world, so wide margins of error are possible. But the "central estimate" averaged out for each country allows for fascinating comparisons.
While it says 96 per cent of Britain's cropland is likely to be more suitable for agriculture in a much hotter world at the end of the century, in France, only 4 per cent of agricultural land will be more suitable, while 55 per cent is likely to be worse.
Looking at the number of people likely to be affected by increased "water stress" - effectively water shortages - France will find 14 per cent of its population affected, while Britain will find 24 per cent.
Some countries are likely to fare much worse than others. Spain, already forecast to become much more arid, stands out in terms of how much of its cropland will become less suitable for agriculture, with an average figure from all the computer predictions of 99 per cent.
Australia and Turkey are close behind, with 97 per cent of their cropland facing degradation, followed by South Africa with 92 per cent.
Britain is likely to benefit most; its 96 per cent increase in suitability is approached only by Germany at 71 per cent, then Canada at 61 per cent, Peru at 60 per cent and Russia at 40 per cent.
In terms of future water stress, no country approaches Egypt's 98 per cent of the population being affected. Spain comes next with 58, Turkey with 45.
For inland flooding, some countries face a gigantic percentage increase in risk, with Kenya leading the way with a 356 per cent increase, followed by India with a 272 per cent increase.
For coastal flooding, India is facing the highest increased risk, with 15.7 million more people likely to be affected by the turn of the century.
"This report highlights some of the very real dangers we face if we don't limit emissions to combat the rise in global temperature," said Huhne.