Comment by lisasays | Hacker News Reader

Comment by lisasays | Hacker News Reader

Not to minimize, but to put in perspective (from the article):

But because the world's oceans are so huge, the melt just from the ice sheets since 1992 still only adds up to a little less than inch (21 millimeters) of sea level rise, on average. Globally sea level rise is accelerating and melt from ice sheets has gone from contributing 5% of the sea level rise to now accounting for more than one-quarter of it, the study said. The rest of the sea rise comes from warmer water expanding and melt from glaciers.

Though they're happy to call this "devastating", and it sure does sound bad -- that label by itself isn't helpful, because it doesn't tell what danger we're facing and how much time we have to brace for it.

That is -- it's sounding the alarm, without providing specifics as to what even the approximate level of danger to anyone's survival is, in real terms. Which probably has a lot to do with why this stuff barely gets reported, and why people mostly shrug when they hear about it (on top of the psychological and other sources of denial).

Fresh water melt-off isn't about rising sea levels, at least not in the short term, it's about the shutdown of ocean circulation.

The repercussions are basically an increase in warming and a decrease in sea-life. The effects of these will be more temperamental weather, and less fish to eat.

https://e360.yale.edu/features/climate-change-ocean-circulat...

Mechanism: > The conveyor is driven by the descent of cold, salty water to the ocean floor in just two places: in the far North Atlantic near Greenland and in the Southern Ocean around Antarctica. In both regions, the mechanism is the same. In cold polar conditions, large volumes of water freeze. The salt in the water is not incorporated into the ice. It remains in the residual liquid water, which grows ever saltier. The saltier water becomes, the denser it becomes. So the residue is heavier than surrounding water and eventually sinks to the ocean floor.

Consequence: > If there was no new deep water plunging to the ocean depths, however, there would be nothing to bring the nutrients back to the surface. Instead, the waters of the deep ocean would accumulate nutrients and become stagnant, while the supply of nutrients to sustain marine life at the surface would be drastically reduced, says one of the paper’s co-authors, Adele Morrison of the Australian National University. Marine ecosystems could collapse. This would not happen instantly. It might take centuries, but once in train could not be prevented.

Consequence: > A shutdown would also accelerate global warming, says Rahmstorf. “The deep-water formation sites are conduits where carbon dioxide is brought down to the ocean abyss, where it is locked away safely from the atmosphere for centuries [and] currently helps slow down global warming. However, this mechanism is set to be weakened.” The IPCC estimates that the oceans altogether capture a quarter of our CO2 emissions, much of it through deep-water formation.

Thank you - that was infinitely more helpful than the original article.

And I am now suitably terrified.

well the conclusion is always the same and the authors work backwards from it so that they can receive funding, and it benefits them and the politicians who give them funding if you remain terrified, so that seems like it's working as intended

the GP makes a bunch of assumptions about systems that science barely has any understanding of

maybe in order to survive life will have to return to a pre-industrial state, but if that's the case and you think "humanity needs to act now" the only thing you could be possibly advocating for is genocide.

> well the conclusion is always the same

From the link I posted:

> Meanwhile the long-standing concern about a shutdown of the ocean circulation in the North Atlantic sometime in the 21st century appears to be subsiding. A Swiss study[1] published this month found that, contrary to past belief, the circulation did not fail at the end of the last ice age, suggesting, the researchers say, that it was more stable than previously supposed, and less likely to collapse. [1] - https://www.unibe.ch/news/media_news/media_relations_e/media...

We're figuring this out all the time. We know change is happening because of human action. We know this will alter the status quo. For greenhouse gases we know this will involve general global temperature increases. Figuring out the precise results takes some work.

I’m confused, if the “concern is subsiding” then how do you conclude in your previous comment that “once in train could not be prevented”?

Those ideas seem to be at odds and support the suggestion that the conclusions of climate science are always the same: doom.

I can’t understand why these sort of studies don’t take a probabilistic or temporal approach to their conclusions. In this way they could be better used to inform policy, in their current state they just instill fear. Something like “we calculate P=0.9 for circulation collapse to begin by 2050. To reduce this P to <0.02 would require emission reduction to accelerate by an additional 10% per year” would actually be actionable, and allow further debate to solidify findings.

If you told me P=.99 for collapse of ocean ecosystems I would be much more likely to listen than if you tell me “ocean current destabilisation is ‘worse’/‘better’ than we thought.

Concern about the North Atlantic circulation is decreasing. Concern has just been sparked about the Antarctic circulation. Different parts of the globe. Also, those are quotes, not my own conclusions.

If I read these articles right, I believe the North Atlantic circulation may slow, but it's not going to stop. And what is predicted to happen in the Antarctic is predicted to be worse than whatever happens in the North Atlantic.

How does one find a P-value for the accuracy of a model, when all of the parameters are not known?

I'd be happy to be corrected but I think you would generate P-values the same way you check the accuracy of all climate models, you use the model to make predictions about the past and compare them to measured values.

If model parameters are unknown, you should be doing a sensitivity analysis on these parameters anyway (you must have already estimated values for these to run your model in the first place).

Once you have a measure of the uncertainty of your model and sensitivity to unknown parameters, you can combine this with probabilities of different warming scenarios (maybe from IPCC data), and determine the likelihood of the circulation stopping given current emissions/warming trends.

Thanks. You know more than I do about statistics.

Global average rise seems like an uninteresting point. We recently read that on the highly populated US Gulf Coast, sea level rise was +5 inches since 2010, which is rather a lot. These are rates that amount to a noticeable difference in one lifetime.

Very much so. Sea level has actually been falling on the coast of Greenland, for example, due to the gravitational effect of ice melting along with crustal rebound. But all that water has to go somewhere, and along low lying coastal areas like Florida, it will rise a lot.

Here's the top line argument. Our environment is a complex dynamic system, massive change over a short time period can have devastating effects. We only have one planet to live on, so we shouldn't gamble with it in this way.

Put another way, you shouldn't walk around eating random substances you find because no one has proven to you that it won't cause harm.

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