Possible climate futures

The global surface temperature will continue to increase until at least the mid-century under all emissions scenarios considered. Global warming of 1.5°C to 2°C will be exceeded during the 21st century unless deep reductions in carbon dioxide (CO2) and other greenhouse gas emissions occur in the coming decades.

The last time the global surface temperature was sustained at or above 2.5°C higher than 1850–1900 was over 3 million years ago.

Many changes in the climate system become more severe due to increasing global temperatures. They include increases in the frequency and intensity of hot extremes, marine heat waves, and heavy precipitation, agricultural and ecological droughts in some regions, and the proportion of intense tropical cyclones, as well as reductions in Arctic sea ice, snow cover and permafrost.

The additional warming is projected to further amplify permafrost thawing, and loss of seasonal snow cover, land ice, and Arctic sea ice. The Arctic is likely to be practically sea ice free in September at least once before 2050.

The Arctic is projected to experience the highest increase in winter temperatures, at about 3 times the rate that the rest of the world is experiencing.

Continued global warming is projected to further intensify the global water cycle, including its variability, global monsoon precipitation and the severity of wet and dry events.

A warmer climate will intensify very wet and very dry weather and climate events and seasons, with implications for flooding or drought.

Many changes due to past and future greenhouse gas emissions are irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level.

In the long term, the sea level will rise for centuries to millennia due to continuing deep ocean warming and ice sheet melting, and will remain elevated for thousands of years. Over the next 2,000 years, the global mean sea level will rise by about 2 to 3 m if warming is limited to 1.5°C, 2 to 6m if limited to 2°C and 19 to 22 m with 5°C of warming.