By 2100 what is the consensus opinion as to how high sea levels will likely have risen?
Consensus assessments put global sea level roughly 0.3–1.3 m higher by 2100 — at least 0.3 m even with the lowest emissions, and up to ~2 m if Antarctic ice collapse accelerates.
The new Thwaites result is part of why high-end estimates keep climbing: a single glacier could add ~30 mm, twice what models previously projected.
4 details5 sources2 disagreements
- NOAA's 2022 interagency task force: even on the lowest-emissions path (1.5°C), global mean sea level rises at least 0.3 m (1 ft) above 2000 levels by 2100; on a very high-emissions path with rapid ice-sheet collapse, it could reach 2 m (6.6 ft).
- An expert survey in npj Climate and Atmospheric Science gives likely ranges of 0.30–0.65 m under RCP2.6 and 0.63–1.32 m under RCP8.5 by 2100 (relative to 1986–2005), with a median of 0.93 m for high emissions.
- A structured expert judgment study in PNAS puts the ice-sheet contribution alone at a median of 26 cm for a +2°C world and 51 cm for +5°C; adding thermal expansion and glaciers pushes the 95th percentile total above 2 m.
- The new Thwaites model, published in Nature Communications, doubles that glacier's projected contribution to ~30 mm by 2100 — roughly twice the ISMIP6 ensemble mean of 15.2 mm.
Room for disagreement
- The main split is over the upper tail: some experts (PNAS survey) see a real chance of >2 m by 2100 under high emissions, while the NOAA task force and IPCC-style model ensembles treat multi-meter rise by 2100 as unlikely, seeing it as a later-century risk.
- The Thwaites result itself is contested: co-author Eric Rignot argues the grounding-zone physics is missing from most models and projections are too low, while British Antarctic Survey's Robert Larter cautions the subglacial environment is more complex than the model assumes and needs direct measurement.
Okay well, that doesn't sound that bad. How many levees and dikes do you think we'll need to build to prevent overflow into cities and stuff that are by the ocean?
There is no single number, but shielding all vulnerable coastal cities would mean building and upgrading tens of thousands of kilometers of levees and sea walls — at a cost in the trillions of dollars — and even then it wouldn't fully prevent overflow.
Hardening every coastline is physically and financially impossible; the real choice is which cities to defend and which to retreat from.
4 details3 sources2 disagreements
- One global analysis estimated that protecting the world's coastlines against a 1-meter sea-level rise could require roughly 50,000 km of new or upgraded levees and flood barriers.
- Cost estimates for coastal protection run into the trillions of dollars: the U.S. National Climate Assessment and similar studies put the price of defending major U.S. coastal cities alone at hundreds of billions to over $1 trillion.
- Even with levees, cities face overflow from storm surge, groundwater seepage, and rainfall flooding — water that gets around or under barriers, which is why places like New York, Rotterdam, and Jakarta are combining walls with elevated land, pumps, and planned retreat.
- The new Thwaites study adds to the problem: its 30 mm contribution by 2100 is only one glacier, and total global sea-level rise of 0.5–1.9 m under high emissions means defenses must be built to far higher standards than most existing ones.
Room for disagreement
- Some engineers argue mega-barriers like the Thames Barrier or the MOSE system in Venice can protect major cities for decades, while others say these projects are too slow and costly, and that managed retreat is unavoidable for many coastal areas.
- Estimates of how much protection is needed diverge widely because they depend on emissions scenarios and on how much risk society accepts — a 0.5 m rise requires far less defense than a 2 m rise, and the new Thwaites findings push upper-end projections higher.
Well if we're talking a slow 100-year progression, I think we'll be able to figure it out.
I'll search for evidence on sea level rise acceleration, locked-in commitments, and adaptation limits to answer this skeptical follow-up.
0
AI answers with web search. May be wrong.
