Top climate scientists have warned the world's political leaders to get ready for more dangerous and "unprecedented extreme weather" caused by global warming.
Making preparations, they say, will save lives and money.
Otherwise weather extremes may overwhelm some locations, making some places uninhabitable.
The Nobel Prize-winning Intergovernmental Panel on Climate Change issued a new special report on global warming and extreme weather after meeting in Kampala, Uganda.
This is the first time the group of scientists has focused on the dangers of extreme weather events such as heatwaves, floods, droughts and storms.
"We need to be worried," said one of the study's lead authors, Maarten van Aalst, director of the International Red Cross/Red Crescent Climate Centre in the Netherlands.
"And our response needs to anticipate disasters and reduce risk before they happen rather than wait until after they happen and clean up afterward. ... Risk has already increased dramatically."
The report said "a changing climate leads to changes in the frequency, intensity, spatial extent, duration, and timing of extreme weather and climate events, and can result in unprecedented extreme weather and climate events". And it said that some - but not all - of these extreme events are caused by the increase of man-made greenhouse gases in the atmosphere.
"We face many challenges in the future," another study lead author, Chris Field of Stanford University, said in a news conference. Those include floods, drought, storms, and heatwaves.
Mr Field said scientists aren't quite sure which will be the biggest threat to the world because disasters are weather extremes interacting with economics and where people live. Society's vulnerability to natural disasters, aside from climate, has also increased, he said.
He said in an interview that "it's clear that losses from disasters are increasing". And in terms of deaths, "more than 95 % of fatalities from the 1970s to the present have been in developing countries," he said.
Losses are already high, running at as much as 200 billion dollars (£126 billion) a year, said Michael Oppenheimer of Princeton University, a study author.
"Global warming is increasing the risk of disaster and already makes dealing with several types of disaster, like heatwaves, more difficult. The risk will become greater as the future gets hotter," he said.
Science has progressed so much in the last several years that scientists can now attribute the increase in many of these types of extreme weather events to global warming with increased confidence, said study author Thomas Stocker at the University of Bern.
The report said it is "virtually certain" that heatwaves are getting worse, longer and hotter, while cold spells are easing.
What that means is the nasty heatwave that used to happen once every 20 years by mid-century will be once every five years and by the end of the century will be an every other year scorcher, Field and Stocker said.
The report said there is at least a two-in-three chance that heavy downpours will increase, both in the tropics and northern regions, and from tropical cyclones.
The 29-page summary of the full special report - which will be completed in the coming months - says that extremes in some unnamed regions at some point in the future can get so bad that they may need to be abandoned.
Such locations are likely to be in poorer countries but even in some developed northern regions of the world, such as Canada, Russia and Greenland, cities might need to move because of weather extremes and sea level rise from man-made warming, Mr van Aalst said.
Scientists emphasised that governments have to be more prepared.
"Governments are not doing a good job now protecting us from disaster in the current climate," Mr Oppenheimer said.
Of all the weather extremes that kill and cause massive damage, he said, the worst is flooding.