The document, published in Paris after a session of the Intergovernmental Panel on Climate Change (IPCC), says the number of climate migrants could total 200 million by 2100.
The report also said the average global temperature will climb by 1.8-4 degrees Celsius (3.2-7.2F), which will cause the world's oceans to rise by 18-59cm by the end of the century. Heat and drought periods will become more frequent.
The warm period, cause by manmade carbon dioxide emissions into the atmosphere, will last for at least 1,000 years, the report said.
The IPCC was established by the World Meteorological Organization (WMO) and the UN Environment Program (UNEP) in 1988, and is widely considered the main global authority on climate science. Its reports are widely cited in debates on climate change.
Georgy Golitsyn, Russia's chief climate scientist, has linked the record warm January in Russia to climate change.
Moscow's chief meteorologist said Thursday that last month was the mildest January the Russian capital has ever had since formal weather observations began 130 years ago.
Alexei Lyakhov said the month's average temperature was just minus 1.6 degrees Celsius, 7.6 degrees above the norm.
