The world faces a "bleak future" without action to tackle climate change, campaigners warned ahead of a major new report on the impacts of global warming.
The latest study from the Intergovernmental Panel on Climate Change (IPCC) is expected to warn of damage to food supplies, livelihoods, health and security across the world.
Ahead of the report's publication, environmentalists called on politicians to break the world's dependency on fossil fuels to prevent catastrophic climate change.
Rising global temperatures, droughts and heat waves will threaten food supplies and human health, while hundreds of millions of people will be affected by coastal flooding, a ccording to leaked versions of the report, which is published on Monday.
Climate change will cause economic losses, exacerbate poverty and increase migration and risks from violent conflict as well as causing damage to wildlife and habitats, the study by experts from around the world is expected to warn .
In Europe, heat waves, droughts and heavy rainstorms will increase and there will be a greater risk of coastal and river flooding, it is expected to say, while heat-related deaths will also increase.
Friends of the Earth's executive director Andy Atkins said: "We face a bleak future if the world continues to ignore the grim scientific warnings of our failure to tackle global warming.
"Droughts, floods and famines are just some of the devastating effects that people around the world are already suffering from more frequent extreme weather - and, unless we take urgent measure, it will get far worse.
"We have the ability to build a cleaner, safer future, but our leaders lack the courage to act.
"Politicians must break our dependency on coal, gas and oil - and stand up to the fossil fuel industry which is powering the planet towards catastrophic climate change."
Sally Uren, chief executive from Forum for the Future, which advises businesses and governments on sustainability, said: "The IPCC report should be read as a vital wake-up call.
"It is now more clear than ever that the risk to society from climate change is real and that large-scale action is needed now, by all of us, to both cut our carbon emissions, and also to accelerate the pace at which we adapt to a rapidly changing climate.
"The report should be taken as a stark reminder of our utter dependency on the natural world. Access to food, water and shelter is a basic human need. Climate change threatens to prevent this access, in the developed and developing world alike.
"We can't and shouldn't put our faith solely in governments to fix the mess we are in. The solutions we need to see for both effective mitigation and adaption will also need to come from wider civil society, and from business," she added.
Rob Elsworth, climate and policy analyst at aid agency Cafod, said: "The IPPC report along with the evidence we're seeing on the ground in developing countries shows climate change is the single biggest threat to poverty reduction that exists today.
"It has the potential to undermine years of hard-won gains in improving the lives of some of the world's poorest people.
"We have the means to end poverty within our lifetimes, but not if we don't tackle climate change, by cutting our emissions and helping poor people to cope with its impacts."