Three UK groups studying climate change have issued an unprecedented statement about the dangers of failing to cut emissions of greenhouse gases.
The Royal Society, Met Office, and Natural Environment Research Council say the science underpinning climate change is more alarming than ever.
They say the 2007 UK floods, 2003 heatwave in Europe and recent droughts were consistent with emerging patterns.
Their comments came ahead of crunch UN climate talks in Copenhagen next month.
'Loss of wildlife'
In a statement calling for action to cut carbon emissions, institutions said evidence for "dangerous, long-term and potentially irreversible climate change" was growing.
Global carbon dioxide levels have continued to rise, Arctic summer ice cover declined sharply in 2007 and 2008, and the last decade has been the warmest on average for 150 years.
Persistent drought in Australia and rising sea levels in the Maldives were further indicators of possible future patterns, they said.
They argue that without action there would be much larger changes in the coming decades, with the UK seeing higher food prices, ill health, more flooding and rising sea levels.
Known or probable damage across the world includes ocean acidification, loss of rainforests, degradation of ecosystems and desertification, they said.
In 2007, the Intergovernmental Panel on Climate Change warned the world faced more droughts, floods, loss of wildlife, rising seas and refugees.
But Prof Julia Slingo, chief scientist of the Met Office, Prof Alan Thorpe, chief executive of Nerc, and Lord Rees, president of the Royal Society, said cutting emissions could substantially limit the severity of climate change.
Meanwhile, a White House official has said the US will announce a target for reducing greenhouse gas emissions before next month's Copenhagen summit.
President Barack Obama has not yet decided whether to attend.