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Comment by paulbaumgart | Hacker News Reader

How much wiggle room is there in the conclusion that this is level of sea level rise is going to happen “regardless of twenty-first-century climate pathways”?

For example, and setting aside feasibility, if carbon dioxide levels were reduced back down to pre-industrial levels, would that amount of sea level rise still be locked in? Or would the ice stop melting and even gradually re-freeze?

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It depends on who you ask, but I've seen estimates that suggest at least 10m of sea level rise is already "priced in", so to speak.

In the climate crisis discussion communities there's a saying that things are happening "faster than expected", which also applies to the fact that most of the accepted climate models are much more conservative than they should be. The IPCC models (for example) largely ignore tipping points and methane emissions, and their contribution to the exponential rate of increase in climate change.

At this point we're not going to do what's needed to make things less bad (i.e., keeping the carbon in the ground) so my suggestion is to plan for the worst and hope for the best.

Is there a map somewhere that simulates various coastline changes based on sea level rise?

Ex: the 10 meters mentioned above

Good question, there are several, but the one I've played with is this tool from the NOAA: https://coast.noaa.gov/slr/

I've used this tool to inform my decisions with regard to planning for my climate mitigation strategy.

A better question would be, is there a map that shows the extended inland reach of the more violent storms that we will get with a warmer atmosphere?

Planning on the basis of the ocean being a mill-pond won't go very well.

Both are important. New York City becoming an oyster bed is a catastrophic migration crisis waiting to happen.

It all depends on how long you want to wait. Last time CO2 levels were as high as today was the mid-Pliocene, with temperatures estimated 2-3C higher than today and sea levels estimated 16 meters higher than today. A slow steady melt of Greenland and West Antarctica would take hundreds or thousands of years:

> "We acknowledge that this sea-level rise would not happen overnight. It would take hundreds to thousands of years to melt such large amounts of ice. Another important finding of our study is that, under temperatures ~4 °C higher than pre-industrial values and elevated CO2 during Pliocene Climatic Optimum, the global mean sea level reached 23.5 m (with an uncertainty range of 9.0-26.7 m) higher than present. This indicates that significantly more ice will melt if temperatures stabilize at this level. This estimate can serve as a target for future ice sheet model calibrations."

https://thesciencebreaker.org/breaks/earth-space/pliocene-se...

This particular article seems to point to 2-3 meter sea level rise by 2100, which looks to be on the higher end of what NOAA puts on their website as the 'observed trend', which looks more like a 1-3 ft sea level rise estimate by 2100. According to their graphics, by 2030 or 2040 it should be more clear which way things are really going, real-world evidence wise.

https://www.climate.gov/news-features/understanding-climate/...

While I can see the logic behind how long it would take to melt all this ice, what about the risk that it will suddenly (in the long view) slide off and start floating around? That will raise sea level by the same amount without needing to melt.

It's worth noting, the last time there was this much CO2 in the atmosphere (>400ppm), sea levels were significantly higher. Estimates are all over the map, but most of them put global sea at least 10m above our current levels.

A few sources:

https://www.noaa.gov/news-release/carbon-dioxide-now-more-th...

https://www.nature.com/articles/s41586-019-1543-2?proof=t

https://www.science.org/doi/10.1126/science.1233137

https://royalsocietypublishing.org/doi/10.1098/rsta.2012.029...

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/200...

EDIT: Fix words.

I mean, if you waved a magic wand and CO2 levels were back at 280ppm? Maybe you'd expect sea levels to stabilize at their current levels?

There's at least four pieces of inertia here that make preventing sea-level rise hard absent such a magic wand:

1. We're not at equilibrium temperature for our current CO2 levels; if you stopped generating CO2 at an industrial scale and we kept the atmosphere to 420ppm CO2, you'd still expect to see the mean global temperature rise.

2. Even absent increases in CO2, the ice that continues to melt until the new equilibrium is reached decreases the reflectivity of the Earth.

3. The ice that's already melted has decreased the weight on the continental places upon which it rested; the plates are still rebounding, and it can be easier for ice to fall off as they raise.

4. Once we reverse course and ice is no longer melting, it will take a long time for the ice to re-form and the water to be removed from the oceans, lowering sea-levels (and storm surges). Some of the places the ice is disappearing from is effectively a desert, with very low rates of precipitation.

5. The ocean has warmed, and it would take time to cool down again. That will continue to affect Greenland for a century or more.

Oh yeah, a goodly portion of the sea level rise is thermal expansion, isn't it?

> We're not at equilibrium temperature for our current CO2 levels; if you stopped generating CO2 at an industrial scale and we kept the atmosphere to 420ppm CO2, you'd still expect to see the mean global temperature rise

Exactly.

We're really in uncharted territory. The IPCC et al can show the results of models etc but nobody really knows how bad things are going to get, even if a miracle happened and we reached zero emissions today.

Last time the Earth was above 400ppm of CO2 was during the Pliocene Epoch (2-5 million years ago). Temps were 2-3ºC higher and sea level was about 30 feet higher. We're now at about 420ppm and rising.

>How much wiggle room is there in the conclusion that this is level of sea level rise is going to happen “regardless of twenty-first-century climate pathways”?

No wiggle room.

https://www.e-education.psu.edu/earth107/node/1496

20,000 years ago we had the last glacial maximum aka ice age. Water levels increased 130 metres since. Your cities like "atlantis" were coastal cities gobbled up by rising water. Noah's ark was just this. When graphs are showing sea level rise over the last 200 years, they are illegtimately trying to imply the industrial age caused it. It has been a process that started 20,000 years ago. In fact, sea level rise hasn't changed at all during industrial age. Same rate nonstop.

So it's not really part of the 'excess carbon' problem but rather a natural process we cant stop.

Therefore you better not be a rich person living on the coast.

Global trend is higher population in cities. So the actual big scale problem is placing cities on shores, in historical flood zones, not minding historical records & ancestral wisdom, then blaming climate for own short-sightedness. Not changes in general but the inertia & radical fast-fixes with ability to create new problems never before existing.

Humanity can adapt to anything. But building non-durable way, consuming wastefully, getting away from nature & living in virtual "civilised" bubbles far from material reality is only asking for troubles when Earth & Sun reminds who truly rules here..

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