Key takeaways
- Some future rise is locked in, about 15 to 30 cm globally by 2050, relative to 1995 to 2014, under any scenario.
- By 2100, global rise of roughly 0.3 m to 1 m is likely, depending on emissions.
- Ice sheet behavior, especially in Antarctica, is the biggest source of uncertainty.
More rise is already on the way
Because the ocean and ice sheets respond slowly to warming, sea level will keep rising for centuries even if emissions stop. Global sea level is likely to be about 15 to 30 cm higher in 2050 than the 1995 to 2014 average under every emissions scenario, because that rise depends mostly on warming that has already happened. After 2050, the choices we make about emissions matter more and more.
What the projections say
The IPCC Sixth Assessment Report projects global sea level by 2100, relative to 1995 to 2014, of:
| Emissions scenario | Likely range by 2100 |
|---|---|
| Very low (SSP1-1.9) | 0.28 to 0.55 m |
| Low (SSP1-2.6) | 0.32 to 0.62 m |
| Intermediate (SSP2-4.5) | 0.44 to 0.76 m |
| High (SSP3-7.0) | 0.55 to 0.90 m |
| Very high (SSP5-8.5) | 0.63 to 1.01 m |
A rise close to 2 m by 2100 and 5 m by 2150 under very high emissions cannot be ruled out, because of deep uncertainty about how quickly the Antarctic ice sheet could collapse.
Why the range is so wide
Most of the spread in projections comes from two sources: how much we emit, and how the ice sheets, especially Antarctica, respond. Thermal expansion and glacier melt are fairly well understood. Ice sheet processes such as the collapse of ice cliffs and the retreat of glaciers on bedrock that slopes downward inland are much harder to predict.
Scenarios, warming levels and low likelihood outcomes
Scenarios versus warming levels
Projections can be organized by emissions pathway (the SSP scenarios) or by how much the planet warms (1.5, 2, 3, 4 or 5 °C). Warming levels are useful for planning because they do not depend on assumptions about when the world reaches a given temperature.
The 2022 U.S. interagency scenarios
For the United States, NASA, NOAA and partner agencies built five scenarios, from Low to High, that span 0.3 m to 2.0 m of global rise by 2100, and translated them to every U.S. coastline. They found that the U.S. coast will likely see 25 to 30 cm of rise between 2020 and 2050, about as much as in the entire previous century. The Coastal Sea Level Explorer shows these scenarios for U.S. tide gauges.
Commitment and overshoot
Even if global temperatures are brought back down after overshooting a target, sea level continues to rise. The deep ocean keeps absorbing heat for centuries, and ice sheets that have started to retreat may not regrow for millennia. Over the next 2,000 years, the IPCC finds that global sea level will rise by about 2 to 3 m if warming is limited to 1.5 °C, and by 2 to 6 m if it is limited to 2 °C.
Watching for change
Comparing observations with projections is one of the best ways to test them. So far, the observed rise since the 1990s tracks the middle of the projected range. Continued satellite measurements will tell us early if the ice sheets begin to move toward the faster end.
References: Fox-Kemper, B. et al. (2021), Ocean, Cryosphere and Sea Level Change, in IPCC AR6 WG1. Sweet, W.V. et al. (2022), Global and Regional Sea Level Rise Scenarios for the United States, NOAA Technical Report NOS 01.