Agricultural pests and diseases are set to increase over the next 40 years due to climate change, says a major report.
Farmers face droughts and floods, increased heat stress in livestock, more storm damage and increased risks from pests and diseases.
But yields could increase with higher temperatures and the opportunity to grow new crops, says UK Climate Projections 2009 report.
Reducing greenhouse gas emissions is critical to avoid exacerbating climate change but past emissions mean some changes is now inevitable, it says.
Experts used the latest climate science to develop the projections, which show likely changes in temperature, rainfall, sea-level, humidity, cloud, and radiation.
Summers are likely to be over 2°C hotter in southern England by the 2040s, accompanied by a 20% drop in summer rainfall.
Winters are likely to be wetter, with winter rainfall increasing by a similar amount in north-west England and Scotland.
The document was launched on Thursday (18 June).
DEFRA secretary Hilary Benn said: “There is no doubt about it – climate change is the biggest challenge facing the world today.
“Climate change is already happening – the hottest 10 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.”
Mr Benn said the government was already tackling climate change through a series of measures.
They included doubling spending on flood protection since 1997, developed a heat wave plan in the NHS and is helping communities affected by coastal erosion.
But the Conservatives said further action was vital.
“Effective measures require more than setting targets,” said shadow farm minister Jim Paice. “Practical steps to de-carbonise the UK’s economy are now essential.”
He added: “The impact of rising temperatures on our natural environment, agriculture and water resources will be significant, and it could be severe.
“We are already facing biodiversity loss and water shortages in many areas.”