Guest yawn by David Middleton

When I first read this, I was all set to ridicule it mercilessly… until I noticed the timeline…

INHERIT THE WATER —
It keeps going: 1 meter sea-level rise by 2300 is now inevitable
Analyzing a longer timeline, even if we ceased emissions in 2030.

SCOTT K. JOHNSON – 11/7/2019

Climate change is often discussed in reference to where things will be in 2100, but the story obviously doesn’t end that year. Sea-level rise in particular has an impressive amount of inertia, and a very long time will pass before it has played out fully. What will our emissions have set in motion on longer time scales?

Projecting sea-level rise in the year 2100 is difficult enough, partly because the behavior of the world’s ice sheets and glaciers is varied and complex, and partly because it depends in a big way on how much greenhouse gasses we continue emitting. Take future emissions off the table, though, and it’s possible to think about what happens out to 2300.

The future is real

That’s what a team led by Alexander Nauels did in an analysis based on a combination of our past emissions and the current Paris Agreement pledges for emissions through 2030. Nauels and his colleagues used a simple mathematical model calibrated against the results published in the most recent IPCC report. Rather than running a massive global simulation on a supercomputer, they calculated the relationship between emissions and sea-level rise in previous simulations—which projected out to the year 2300. This also allowed them to quickly process multiple variations of their question.

Considering only emissions through 2030 creates a hypothetical scenario in which warming peaks around 1.5 °C above preindustrial temperatures and starts dropping before the end of this century. This results in about 43cm (17 inches) of sea level rise by 2100, and 105cm (41 inches) by 2300. That’s what greenhouse gas emissions through 2030 commit us to, even if we emitted nothing after that.

[…]

SCOTT K. JOHNSON
Scott is an educator and recovering hydrogeologist who has been covering the geosciences for Ars since 2011.

ARS Technica

Could sea level rise by about 1 meter by 2300? Sure. At the current rate of about 3.2 mm/yr, it’s rising 320 mm per century… 960 mm from 2001-2300 is almost 1 meter. Sea level has been more than 1 meter higher than today for most of the past 3,000 years.

That said, forecasts of sea level rise that far out in the future are pointless. According to the “analysis” of the “team led by Alexander Nauels,” even if we halt all emissions by 2030, sea level will rise 43 cm (17 inches) by 2100. In their paper, Mengel et al. assert a 43 cm sea level rise (SLR) by 2100 under RCP2.6. That’s 4.3 mm/yr. We’re already nearly 20 years into this time span and SLR is stuck on 3.0 mm/yr over the entire satellite record.

I broke out the past five years because the World Meteorological Organization recently asserted that it had accelerated to 5 mm/yr over the past 5 years, a claim that is utter horst schist.

For sea level to rise by 43 cm (430 mm) over the 21st century, it would have to average 4.6 mm/yr over the next 80 years. If it started accelerating now, it would have to accelerate to 4 mm/yr by 2034, 5 mm/yr by 2065 and 6 mm/yr by 2096… But it would actually have to start accelerating. No… Neither Church & White’s, nor Nerem’s recent claims of SLR acceleration alter what the satellite data clearly demonstrate: The R² of the linear trend over the entire satellite record is 0.95… About as close to unity as nature can get.

References

Brock, J.C.,  M. Palaseanu-Lovejoy, C.W. Wright, & A. Nayegandhi. (2008). “Patch-reef morphology as a proxy for Holocene sea-level variability, Northern Florida Keys, USA”. Coral Reefs. 27. 555-568. 10.1007/s00338-008-0370-y. 

Mengel, M., Nauels, A., Rogelj, J. et al. Committed sea-level rise under the Paris Agreement and the legacy of delayed mitigation action. Nat Commun 9, 601 (2018) doi:10.1038/s41467-018-02985-8