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9273629397759992 OP t1_j8iu67m wrote

Plain language summary:

A team of international scientists has published a study in Nature Communications which warns that if global temperatures cannot be stabilized below 1.8°C, the West Antarctic and Greenland ice sheets will be lost and sea levels will rapidly rise. The study states that this increase in sea level would be on top of other contributions, such as the thermal expansion of ocean water. The study highlights the need for computer models to capture all components of the climate, as well as new observational programs to accurately represent physical processes in the ice sheets. If global net zero carbon emissions cannot be reached by 2060, then sea levels will continue to rise by at least 100 cm within the next 130 years. This would be on top of other contributions, such as the thermal expansion of ocean water.

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grundar t1_j8ke9q1 wrote

It's worth noting that this paper is actually good news, as it predicts lower global sea-level rise contributions from ice melt than previous models did; from the Abstract:
> "The combined effect is likely to decelerate global sea-level rise contributions from Antarctica relative to the uncoupled climate-forced ice-sheet model configuration."

In "Discussion" they call this out specifically for high-emission scenarios:
> "In our high-emission scenario model simulations that include parameterizations for hydrofracturing, ice-cliff instabilities, and capture sea-ice and atmospheric responses, the net impact of ice-sheet/climate feedbacks on SL rise is negative."

It looks to be a fairly marginal change, though; the projected amount of sea-level rise is still enough to be a serious problem, impacting where hundreds of millions of people currently live.

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AndyTheSane t1_j8m2doo wrote

I'm a bit dubious about this; paleogeographic studies point to large (as in around 20m) sea level rises from the kind of temperature rise we've already seen or can project in a few decades. Now, it could be a matter of timing - it might take 1000 years or so for the full ice-sheet response - but it's not exactly reassuring.

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grundar t1_j8nobbf wrote

> I'm a bit dubious about this

What exactly are you dubious about? That the paper predicts lower sea level rise than previous models, or that either way the sea level rise will be enough to have serious consequences?

Your phrasing makes it seem like you're disagreeing with me, but I don't see which part you're disagreeing with.

> Now, it could be a matter of timing - it might take 1000 years or so for the full ice-sheet response - but it's not exactly reassuring.

There's a massive difference between "20m of sea level rise in 80 years" and "20m of sea level rise in 1,000 years".

In particular, my understanding is that paleographic studies are generally of the form "temperature went up 5C and sea level went up 20m over the course of 10ky", meaning sustained temperature increase led to large sea level rise. There's not really any hope of seeing temperatures 80 years from now back to pre-industrial levels, but IPCC scenarios like SSP1-2.6 see temperature starting to fall by then, meaning it could be back to pre-industrial levels within a century or two.

As a result, if a certain amount of sea level rise requires only 80 years of sustained temperature increase of 1.5-2C, we have little hope of avoiding that. By contrast, if that amount of sea level rise requires 1,000+ years of sustained temperature increase of 1.5-2C, there's quite good odds of avoiding some, most, or potentially even virtually all of that.

In general, the known ice melt tipping points take thousands of years. I extracted a list of those tipping points from a paper previously discussed on r/science, and the timescale for 10m+ of sea level rise looks to be about 2,000 years (mainly West Antarctic ice sheet and East Antarctic subglacial basins).

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SeaUrchinSalad t1_j8osz3h wrote

If the water rises slow enough, we might get lucky and find lots of it falling on land and recharging aquifers, which would reduce the amount in the ocean and contributing to the rise. Not by much though

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3trt t1_j8piy0t wrote

That's a stretch. Most global warming models predict droughts. Sure more water will fall in places, but it's not normally where we need it for agriculture or it comes as monsoons and washes away to the ocean as quick as it came.

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SeaUrchinSalad t1_j8q9eqv wrote

Yea we need to get good at hydro geo engineering to capture those monsoons and fast

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californiarepublik t1_j8izc8a wrote

This estimate seems extremely conservative...? Only 100cm in 130 years?

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starmartyr t1_j8jcb13 wrote

That might not sound like much, but it's enough to put dozens of major cities underwater.

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Techie9 t1_j8kxdnq wrote

By my calculations, this predicts about an inch of sea level rise every three years. Hopefully this will give civilization enough time to slowly move away from the current sea level.

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kytopressler t1_j8jbtbd wrote

Their estimate of SLR is the opposite of a conservative one, their estimate is at the upper range of previous estimates. Edwards et al. (2021) provided us with the most up-do-date results from the Ice Sheet Model Intercomparison Project (ISMIP6) for Coupled Model Intercomparison Project Phase 6 (CMIP6).

From Park et al. (2023), this paper,

>For the SSP1-1.9, SSP2-4.5 and SSP5-8.5 scenarios the GrIS contributes about 12 ± 1, 18 ± 0.9 and 23 ± 1.6 cm and the AIS adds 3 ± 0.8, 7 ± 1.4, and 15 ± 1.5 cm to SL by the year 2100 relative to pre-industrial levels (Fig. 2c, d). 2100 CE (2150 CE) LOVECLIP simulates for the respective scenarios a total ice-sheet contribution to SL of 15 ± 0.9, 24 ± 1.3, 39 ± 2 (19 ± 1.4, 48 ± 1.4, 136 ± 6.2) cm (Fig. 2b).

Compare this to Edwards, from Table 1, which reports median and 5th-95th percentiles, under SSP5-8.5 by 2100, the GrIS contributes 10cm [2,20], the AIS contributes 4cm [-4,14].

Note however, that Park is reporting SLR from pre-industrial, while Edwards is reporting post-2015 SLR, which means you would need to subtract the pre-2015 contributions for a complete comparison. This would have the effect of subtracting less than ~1cm from GrIS, and ~2cm from AIS in Park.

In fact, the AIS contribution found in Park is closer to the median in Edwards' worst-case "Risk-averse projection" which combine assumptions that lead to the highest AIS contribution.

In short, this paper's results for 21st century SLR are from from "conservative" in the sense that they actually fall within the upper range of probability of previous research. They themselves note,

>The GrIS and AIS contributions lie within the range of estimates obtained from uncoupled scenario-forced models for Greenland and Antarctica

Edit: A previous version of this comment was in complete error, mea culpa!

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BurnerAcc2020 t1_j8mbcxg wrote

No, I have to say that you misread the paper here.

The first sentence you quoted discusses estimates for the 21st century (i.e. up until 2100), and it explicitly refers to AIS (Antarctic ice sheet) contribution. The actual paper's estimate in the second sentence is by 2150, not 2100, and it refers to ice-sheet contributions - i.e. Antarctic ice sheet and Greenland.

You need to look at Figure 3 of that paper. You'll see that in d), their estimate for AIS alone under SSP5-8.5 (the orange line - the higher yellow line is a more primitive simulation of the same scenario they run for comparison) is about 0.2 m by 2100 and 0.7 m for 2150.

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kytopressler t1_j8np0u0 wrote

Thanks, you're completely right! Very terribly sloppy work on my part. I corrected it, read: completely replaced it, with a comment that actually directly compares apples to apples

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surkacirvive t1_j8lc9ms wrote

It's worth noting that a storm surge that's already 100cm higher will be devastating, not to mention climate change increasing the frequency and severity of storm cycles

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dragonfliesloveme t1_j8kuiby wrote

I mean, the powers-that-be are not even trying to reach zero emissions. Big Oil is still running the world, and they intend to make every last penny from the last drop of oil.

It will be a great day when Big Oil doesn’t run the world. As long as there is a manageable world left.

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