The assessment is the most comprehensive probe yet by the 194-nation Intergovernmental Panel on Climate Change (IPCC) into the impact of climate change on extreme weather events.
A 20-page draft "summary for policymakers" obtained by AFP says in essence that global warming will create weather on steroids.
It also notes that these amped-up events -- cyclones, heat waves, diluvian rains, drought -- will hit the world unevenly.
Subject to modification, the draft summary will be examined by governments at a six-day IPCC meeting starting on Monday in the Ugandan capital of Kampala.
In the worst scenario, human settlement in some areas could be wiped out, the report warns.
"If disasters occur more frequently and/or with greater magnitude, some local areas will become increasingly marginal as places to live or in which to maintain livelihoods," it says.
"In such cases migration becomes permanent and could introduce new pressures in areas of relocation. For locations such as atolls, in some cases it is possible that many residents will have to relocate."
Three years in the making, the underlying 800-page report synthesises thousands of recent, peer-reviewed scientific studies.
The authors expresses high confidence in some findings but stresses uncertainty in others, mainly due to lack of data.
They also emphasise that the vulnerability of human settlements depends as much or more on exposure, preparedness and the capacity to respond as it does on the raw power of Nature's violent outburts.
Average global temperatures have risen by nearly 1.0 degree Celsius (1.8 degrees Fahrenheit) since pre-industrial times, with forecasts for future warming ranging between an additional 1.0 C to 5.0 C (1.8-9.0 F) by 2100.
