And now for the weather. The 2020s are looking warm and dry, with occasional heavy winter showers. The 2050s should be sunny and warm, with scattered deaths due to heatwaves across London and the south-east. And looking ahead to the 2080s, temperatures could reach 41C, so be sure to pack the suncream for your picnic. And watch out for those great white sharks!

Scientists today issued the most detailed assessment yet of how global warming will unfold across Britain. In a range of possible scenarios published by the government, the experts painted a picture of a very different UK, with soaring summertime temperatures and dwindling rainfall.

Announcing the results, Hilary Benn, environment secretary, said global warming will affect "every aspect of our daily lives". The scientists say summer rainfall in south-east England could decrease by a fifth by the 2050s. Average mean temperatures are likely to rise by more than 2C across the UK by 2040s. If carbon emissions continue to rise, there is a 10% chance that temperatures in the southeast could rise by 8C or more by the 2080s.

The results are aimed at industries and organisations that need to make long-term investment decisions that could be influenced by a changing climate. They come as scientists urge politicians to focus on adapting to inevitable climate change as well as on efforts to reduce greenhouse gas emissions.

Benn said: "There is no doubt about it, climate change is the biggest challenge facing the world today. It is already happening, the hottest ten years on record globally have all been since 1990. This landmark scientific evidence shows not only that we need to tackle the causes of climate change, but also that we must deal with the consequences."

The new predictions follow a similar exercise in 2002, that produced maps of likely changes across Britain for the 2020s, 2050s and 2080s. They showed the UK faced drier, warmer summers and wetter, milder winters. Experts say the new results are more powerful, because they present the relative probabilities of a range of possible outcomes. They also cover three different possible futures, in which carbon emissions are low, medium or high. Benn said the world was currently heading along the medium scenario, but that there was a risk that emissions could increase towards the high pathway.

Under the high emissions scenario, the results suggest the hottest summer days could be 12C warmer than today, with peak summer temperatures in London regularly topping 40C.

To produce the new predictions, the scientists at the Met Office Hadley Centre ran 300 versions of their sophisticated climate computer model, and pooled the results to see which outcomes were most likely. The results cannot be used to predict specific weather on future dates, but they indicate broad trends.

Andy Brown, climate change and environmental performance manager with Anglian Water, said the results would help the company plan key infrastructure such as reservoirs. "The increased resolution and probabilities will help to give us more focus." The breakdown into small regions, just 25km across, will help too. "Rainfall can be very localised so it will help us make plans to deal with events."

Paul Bettison, chair of the environment board at the Local Government Association: "We need to start encouraging people to plan for the future. Schools in other countries more used to blistering hot summers are built with large amounts of shade. Our teachers chase people out of shady classrooms to enjoy the sunshine."

Better projections of climate in the 2050s and even the 2080s can help local authorities to force developers to adapt their designs, he says. And existing regulations only insist on a minimum temperature inside buildings such as schools, that is likely to change to include maximum temperature too. "When the original act was written in the 1960s nobody had heard of climate change," he said. "Simply building in dirty great air conditioning units is not the answer."

Paul Williams, a climate scientist at the University of Reading, said: "Sceptics will no doubt question how scientists can confidently predict the climate of 2080, when we cannot even forecast next week's weather with any skill. But climate prediction and weather forecasting are completely different problems. We can say with confidence that July is always warmer than January, because more sunlight is received. Similarly, we can say with confidence that the 2080s will be warmer than the 2000s, because of the extra heat trapped by greenhouse gases."

The Department of Energy and Climate Change said the publication of the new climate predictions marked the first step towards a "five point plan" to tackle climate change. Later this month, Ed Miliband, energy and climate secretary, will publish the government's blueprint for a new global climate deal, which it hopes will be agreed at key UN talks in Copenhagen in December. Next month, ministers will publish a new national strategy for climate and energy, to set out policies to meet the government's domestic carbon reduction targets.

The climate predictions were welcomed by the University of Oxford's Sir David King, the former chief scientific advisor. "Now the question is whether or not the British public and their councillors, planners, civil servants and politicians have the appetite to provide sufficient funding to implement long-range schemes of adaptation across the regions covered by the report."

Green campaigners called for stronger action on emissions to avoid the damaging impacts the UK will face .

Andy Atkins, Friends of the Earth executive director, said: "This valuable new research highlights the damaging impact that climate change will have around the UK . The UK government must show real leadership by example ahead of crucial climate negotiations in Copenhagen."

Chris Smith, chairman of the Environment Agency said: "These new projections remind us starkly of the choices we face in ensuring a sustainable future for our fragile planet. A failure to cut greenhouse gas emissions will lead to a battle for survival for mankind and many other species across the globe by the end of this century."