Hacker News new | comments | show | ask | jobs | submit login
Antarctica loses three trillion tonnes of ice in 25 years (bbc.co.uk)
124 points by open-source-ux 35 days ago | hide | past | web | favorite | 54 comments

Rather than focusing on the big sounding absolute number in the headline, the more important number is the 3-fold increase since 2012. This means that the losses are accelerating, which is very concerning.

Beyond that I wish articles included the total volume of ice in Antarctica; not that I believe 3 trillion tones of lost ice is not a big deal but I have no idea if that represents 1% or 50% of the available total.

It looks like the total amount of estimated ice in Antarctica is something like 30,000,000 cubic kilometers, give or take. In comparison, the amount of ice being lost here probably doesn't even amount to rounding error; it's more like just noise. (Someone else here has calculated a value of about 0.01%, but I don't know how accurate that is.)

That's a common theme with such reports these days, BTW. The numbers quoted can be scary at first, but looking at the bigger picture they often turn out to fall into the margin-of-error/statistical-noise range - a bit disconcerting, maybe, but not something to get too worked up about.

What's more interesting to me is usually what's left out of such reports. For example, there are claims that while ice may be melting around the edges of Antarctica (at least in certain parts of it), a lot of that may just end back up as snow in the interior instead of actually staying in the ocean. And while "warming waters" might be caused by climate change, they might also be due to geothermal activity in and around Antarctica - undersea thermal vents and such. The continent itself should have about the same level of volcanic and geothermal activity that any other continent typically has, which of course ebbs and flows, but it's generally hidden from view under all that ice.

A poor estimate is that 1 trillion tones of ice is 1000 cubic kilometers.

Yeah it's concerning. Now if you'll excuse me, I'll get back to driving my gasoline vehicle and not carpooling.

You don't need us to excuse you, this is an internet comment thread.

For context: there are 26.5 million cubic km of ice in Antarctica, weighing 24.3 million Gt (26.5 / 1.091).

Assuming these estimated 2,700 Gt (the rounded 3 trillion) have not been steadily replaced by new water on top of the ice sheet [1] the reported loss amounts to a mere 0.01% of the total ice sheet.

I don't see cause for panic.

[1] https://www.nasa.gov/feature/goddard/nasa-study-mass-gains-o...

How do you know 0.01% is not a cause for panic?

At that rate it would take 25,000 years for 10% of the Antarctica ice sheet to melt.

On the other hand 20,000 years ago was the peak of the last Ice Age. Sea level was 120m lower than today. There was more ice in the Northern hemisphere's ice sheets than there is in Antarctica. We happen to live in an interglacial, one that is not even as warm as the previous one. It is far more reasonable to fret over the coming return of the Ice Age than to panic about minor variations in a warm, agriculture-friendly climate.

Further, another NASA study indicated in 2015 that the Antarctica ice sheet is growing (not shrinking) by almost 0.01% every 25 years. Did you panic over that report? More generally, is there a specific, perfect, fixed amount of ice that should be in Antarctica? has there ever been? by what standard?

How many feet above current sea level will I have to reside to be safe in 10 years, 20 years?

In fact only the coastal regions will suffer from sea levels rise per se. But no height will be sufficient to guarantee your safety, sadly, because this is not about literal Great Flood. This is about climate change and hundreds of millions of deperate displaced immigrants from places like Bangladesh who will make everywhere more chaotic than today. We're not prepared for the human part of the catastrophe.

> only the coastal regions will suffer from sea levels rise

that's sort of definitional, but what might be 'coastal regions' 50 years from now might be somewhat different than today.

I would bet that even under worst case scenarios + some black swan events 20 feet above sea level is still perfectly safe from sea level rise until 2100, but then you still have increased flooding from extreme rainfall events, draughts, heatwaves, ocean acidification, soil depletion, mass migration, and a number of other future problems that can wreak havok on people just about everywhere.

I don't think they're expecting much in the next decade or two, maybe a few inches?

> the worst-case scenario — of seas rising nearly 4 feet due to Antarctic ice loss alone by 2100 — assumes that very high emissions continue for carbon dioxide and other greenhouse gases


That also assumes the west Antarctic holds together until 2100. That's when it's expected to go into full retreat but the error bars are +-50 years. It could hold until 2150, but it could also start breaking up in 2050. That possibility and others are not included in those estimates.

I believe it's about 9m if the whole of Greenland (two major glaciers) melts. And another ~60m if the whole of Antarctica melts. Naturally this is unlikely to happen in our lifetime, but positive feedback loops are a fascinating subject.

For friends looking to buy coastal property on ~30 year loans I advise that they need to be able to sell those properties some decades out from a more general concern / awareness of the risk.

Don't live close to sea level anywhere that gets hurricanes (Sorry Houston, New Orleans, Tampa and Miami).

From TFA: "Globally, sea levels are rising by about 3mm a year."

That's really, really fast.

It's been a while since I did the math, but IIRC this amounts to maybe half of the historical average rise since the end of the last ice age, where things were at times moving really, really fast. So not really that fast at all in the big picture. BTW, there's no particular reason to believe that this natural rise ever came to a complete halt either, AFAIK.

If it gets worse, it wont matter how many feet you are above sea level, except to not have your house submerged in water.

But the repercussions, like economic downturns, loss of friends and relatives, climate change created phenomena, food and water shortages, diseases on the raise, and so on, will affect everywhere...

If you’re more than like 150 feet above sea level it will never be an issue.

Water submerging your property wont be an issue. All the tons of others far more important repercussions will still apply...

50cm by 2100. That's just under 20 inches for Imperialists.

This assumes a linear rise of 6mm/year.

So in the next 10 years sea level would rise by 6 cm (just over two inches; I understand there are twelve of those in a foot, so we're not talking "feet" until 102 years from now).

That's also average sea level. If hurricanes get more powerful or more frequent, then you're going to want to account for the storm surge as well.

The historical record shows that hurricanes have gotten neither more frequent nor more powerful. [1]

[1] https://www.wsj.com/articles/the-hurricane-lull-couldnt-last...

Perhaps the word "if" doesn't mean what I used it to mean? In that case, you should correct my misconceptions on that subject instead.

The X in your "if X then ..." is demonstrated false. That's your misconception.

The historical record talks about what (a) happened in the past, (b) is on record. Neither applies to a rapidly changing climate landscape.

Science doesn't apply to a rapidly changing, politically charged topic.

It's probably not gonna stay that way tho.

"More thoughtful and effective disaster policies are needed because the future will bring many more weather disasters like Hurricane Harvey, with larger impacts than those of the recent past." (From your own link)

The bigger impact will likely be water stored on land -- e.g. snowpack. All of California's major rivers are fed by snowpack/glacial melt from the Sierras, if all that starts melting more, there will be flooding, and then in later years there will be much less water coming off the mountains (as it'll have already melted).

Also NASA:

Antarctic Sea Ice Reaches New Record Maximum (2014) [1]

NASA Study: Mass Gains of Antarctic Ice Sheet Greater than Losses (2015) [2]

  etc etc etc
[1] https://www.nasa.gov/content/goddard/antarctic-sea-ice-reach...

[2] https://www.nasa.gov/feature/goddard/nasa-study-mass-gains-o...

I think maybe these are worth reading past the title?

[1]: > While the Antarctic sea ice yearly wintertime maximum extent hit record highs from 2012 to 2014 before returning to average levels in 2015, both the Arctic wintertime maximum and its summer minimum extent have been in a sharp decline for the past decades. Studies show that globally, the decreases in Arctic sea ice far exceed the increases in Antarctic sea ice.

[2] "We’re essentially in agreement with other studies that show an increase in ice discharge in the Antarctic Peninsula and the Thwaites and Pine Island region of West Antarctica" ... "“Our main disagreement is for East Antarctica and the interior of West Antarctica" ... "If the losses of the Antarctic Peninsula and parts of West Antarctica continue to increase at the same rate they’ve been increasing for the last two decades, the losses will catch up with the long-term gain in East Antarctica in 20 or 30 years -- I don’t think there will be enough snowfall increase to offset these losses."

No, over years, Antarctic loses total ice, 125 GTons per year on average:


"Sea ice" from the titles you quote is just a subset of "ice" and "extent" is just one dimension of all its presence, and there's constantly less total ice (minus seasonal variation). Your title selection misuses some people's unawareness of the difference.

Oh Dear !!! Climate change is a slow moving disaster which we humans have not evolved to completely comprehend. Once the oceans are not able to absorb any more C02, the temperatures are going to soar pretty fast and that C02 will remain in the atmosphere for a long time (unless some magic carbon capture thing comes along..which I doubt).

Right now ocean currents are near one full turnover from around the start of the industrial revolution. Up until now, as deep ocean currents rose to the surface it was exposing fresh water unladen with excess CO2, but now the current coming up is carrying CO2 saturated water from the industrial revolution.

When I read stories like this I'm instantly reminded how small my day to day problems really are.

I don't understand this part: "In total, Antarctica has shed some 2.7 trillion tonnes of ice since 1992, corresponding to an increase in global sea level of more than 7.5mm."

If the melting ice of Antarctica contributes only 0.3mm per year to the annual 6mm rise of sea levels, what exactly is causing a 20x larger change?

[added] On the other hand a NASA study published in 2015 [1] indicated that Antarctica has been steadily accumulating ice, thereby "taking 0.23 millimeters per year away... If the 0.27 millimeters per year of sea level rise attributed to Antarctica in the IPCC report is not really coming from Antarctica, there must be some other contribution to sea level rise that is not accounted for."

[1] https://www.nasa.gov/feature/goddard/nasa-study-mass-gains-o...

0.3 mm/yr * 26 yr = 7.8 mm

Antarctica's contribution to sea level rise per year is fairly small. The largest portion comes from loss of land-ice like mountain glaciers and snow pack. Mass loss from the Greenland Ice Sheet is also substantial, contributing about 2.7 mm/yr to sea level change. Groundwater withdrawal is a measurable component of modern sea level rise. Aside from these mass-transfer mechanisms, there is also ocean warming (water generally expands as it get warmer) and salinity changes that don't affect the amount of water in the oceans, but do affect its volume. Loss of sea ice (which floats on top of water and is not supported from below by solid earth) does not contribute to sea level change, as the sea ice is already displacing an amount of water equal to the amount of ice doing the displacing.

That 2015 Jay Zwally paper should not be taken as truth, as there are substantial reasons to doubt the impact of the findings. In that paper Zwally uses a set of satellite laser altimeters operating over different epochs and neglects to co-register the different platforms in an intelligent way. There was actually major hubbub around that paper and most glaciologists recognize the claim that "Antarctica is gaining mass" is probably incorrect.[0] Zwally has a pretty big ego and was happy to get the publicity anyways.

[0] https://www.scientificamerican.com/article/what-to-believe-i...

Greenland does not contribute that much to global sea-level rise: "The cumulative ice loss from Greenland from 1992 to 2015 was 3,600 Gt and contributed to global sea level rise by approximately 10 mm" -- that's less than 0.5 mm/year. [1]

Where did you get that Greenland contribution rate?

[1] https://www.eea.europa.eu/data-and-maps/indicators/greenland...

Water expands when it gets warmer.

On the other hand, "In the most recent estimate, for 1993–2008, the contribution from land ice increased to 68 percent, the contribution from thermal expansion decreased to 35 percent". [1]

Something is not right. Either ice melting has been contributing 4mm/year to recent decades of sea rise, or the contribution is slightly negative (in the largest ice sheet, over Antarctica). Thermal expansion of ocean water on its own does not adequately explain it.

[1] Contributions to Global Sea-Level Rise https://www.nap.edu/read/13389/chapter/5


One could dogmatically down-vote, or one could provide references to scientific discussions that cover the contradictory stories... You know who you are.


Check page 291 for an overview of components and time lines. This is still the current scientific consensus AFAIK (no major updates).

Thank you.

The estimated contribution to sea-level rise by thermal expansion of the oceans is 1 mm/year.

It's still not clear how this amount plus the measured contributions of Greenland (under 0.5 mm/year) and Antarctica (0.3 mm, possibly -0.2 mm) somehow add up to a predicted 6 mm/year (or even to a measured 3 mm/year trend).

Here are some things I can think of that may contribute to sea level rise but which I rarely, if ever, see mentioned; the first two are potential anthropogenic causes.

1. Every time you burn a hydrocarbon, in addition to CO2 you also produce H2O. The ratio varies, but in general all of the hydrogen atoms will burn off before all of the carbon atoms do, since carbon-carbon bonds are fairly strong. (This can lead to things like soot.) Much of the water produced ultimately ends up in the oceans.

2. For decades now we've been pumping down aquifers at a fast clip, and that water ultimately ends up in the oceans, too. Natural aquifer replenishment rates may be fairly slow, if they ever replenish at all (the oldest, deepest aquifers may not) and the land-use changes we've made (paving and construction and such) slow that process down ever more.

3. Water from deep subterranean sources maybe be leaking into the oceans via undersea vents and such; this can also lead to bottom-up warming. Ongoing isostatic rebound from the loss of ice mass over the continents may be increasing these factors.

As to ocean warming itself, in general top-down warming only occurs within the uppermost layer of the ocean. (Oceans are dynamic things, of course, so some deeper flow and mixing does occur.) But that top-layer warming is also heavily mitigated by evaporation, where a great deal of the potential heat energy rises up with the water vapor and is eventually lost to space; meanwhile the water itself eventually returns. The clouds produced as the water vapor condenses and loses its heat also mitigate further warming.

Hmm. Let me know when you have some scientific evidence and specific numbers related to these notions.

If we're cooking up stories, how about this arbitrary "explanation": Phytoplankton are plentiful. They're reproducing and dying and sinking in such vast quantities to the ocean floor that this floor is steadily growing a new layer, at a rate of a few mm per year. Hence the apparent sea-level rise, relative to the continents. The accumulation of biogenic sediment is accelerating with the rise in atmospheric CO2 because CO2 directly feeds the plankton.

Am I correct in assuming that you're the type who needs a "study" in order to tell you what to think? Or are you the type who can use their own eyes and their own brain and do their own thinking and come up with their own conclusions - maybe ones that are eventually validated by studies after all, but perhaps only years or even decades down the road?

I consider the first type a form of education-induced brain damage, BTW. And while I'm fairly well-educated myself, I've never been the type who needed the "crutch" of a study in order to figure fairly obvious things out.

I don't remember the details, but I did once try to do the math on the whole CO2:H2O thing, since I hadn't seen it elsewhere. Estimated CO2 emission numbers are routinely published (to the extent that these can be trusted), and I started off with the simplifying assumption that CO2 and H2O are generated in equal amounts. This led to a small but real potential effect on sea level rise. (Although when I once discussed this in another forum some years back, someone there tried to insist that all of that water vapor just stays in the air - which I thought was rather bizarre!) But when I tried to make a more realistic assessment of the situation, I realized just how variable things could be (see examples below), and that I really had no good information to go on. Any numbers I came up with could vary widely based on my starting assumptions, so they weren't really worth very much in the end - kind of like the way so much "climate science" is done today! :)

CO2:H2O production ratios, if fully oxidized. If not fully oxidized then the CO2 numbers drop and soot is produced instead.

Methane: 1:2

Octane: 8:9

Benzene: 2:1

These are for very simple organic molecules. Once you get past a handful of carbon atoms the number of potential molecular configurations and corresponding ratios starts growing dramatically, and for something like coal the situation can grow extremely complex.

I know your phytoplankton comment was meant as sarcasm, but such things might actually have a real effect over time. (You should probably do the math!) The buildup of organic matter, minerals, sediments from erosion, and "rocks" and such might very well be noticeable. Remember that, if land-building forces were to basically come to a halt, then eventually all of the continents would pretty much just erode completely away, leaving not much more than an Earth covered in seawater to some average depth.

The latter, of course! I'd be interested in your numbers. H2O is 2.5% of the atmosphere, so I can't see our CO2:H2O production having a significant impact in that respect; but still, an interesting angle since H2O is a major greenhouse gas.

Estimates for biogenic sediment accumulation ranges up to 5 cm per thousand years -- two orders of magnitude smaller than current prediction of the rate of global sea-level rise.

Unfortunately I did this seat-of-the-pants calculation years ago, so I no longer have the numbers around. I do remember that using the simplistic 1:1 ratio the net result was considerably smaller than I had originally expected, although still measurable. But when I tried to figure out a more realistic ratio to use I kind of ran into a brick wall. See, for example, the typical molecular complexity of coal: https://en.wikipedia.org/wiki/Coal#/media/File:Struktura_che... (It's been a long time now, but if I remember my organic chemistry correctly each of those unmarked corners is a carbon atom, and each of those may have a hydrogen atom attached to it, and possibly more than one.)

A transition away from coal and towards natural gas (which consists primarily of fully-combustible methane at a ratio of 1:2) should lead to both an increase in H2O output and a decrease in CO2 output as compared to coal. (A recent local power plant transition from coal to natural gas claims a carbon emissions reduction of 60%.) Using your 2.5% number, water vapor is already about 60x more common in the atmosphere than CO2 is at 0.041%, and I've seen estimates that it is probably about 15% higher now than it was in the past. (Presumably any H2O output above that has ended up in the oceans.)

Given that as a greenhouse gas water vapor is at least 2x (IIRC) as powerful as CO2 and apparently also increasing at a steady clip, you'd think that folks would be paying more attention to this, but instead they just tend to ignore it. In fact they just like to ignore water vapor completely, except maybe when it leads to clouds and such.

Look... Humanity... You know you could do something about this, right? ... No, faster than that. You can do it faster. You just don't want to, do you? ... Because you're too selfish and short-sighted! Can't you see that? ... Of course you can't. Listen... No, listen... You're f%$&ed. Don't you get it? You're f%$&ed, and you're making it worse, and you're refusing to listen because you're smart enough to fly to the moon, but too dumb to save yourself! Sigh.

I expect to see #FloridaMan stories about sea level rise before we do something constructive like greatly increase the gas tax.

> something constructive like greatly increase the gas tax

and to stop subsidizing meat and dairy production and associated crops (corn, soy).

Why do headlines give meaningless and absolutely context-free numbers just because they sound large?!?! X-(

In other news: you breathe out a bazillion molecules of carbon dioxide every breath!! /rant

this type of news unfortunately won't change the consumerist nature of most people

Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | Legal | Apply to YC | Contact