
Nasa Study: Mass Gains of Antarctic Ice Sheet Greater Than Losses (2015) - iamcurious
https://www.nasa.gov/feature/goddard/nasa-study-mass-gains-of-antarctic-ice-sheet-greater-than-losses/
======
ScottKolo
A few notes before the denial camp arrives:

\- They point out that the Antarctic ice sheet is gaining in mass due to the
melting/compaction of snow from the past 10,000 years, not because of anything
having to do with global temperatures.

\- Ice losses to calving (ice breaking off and falling/drifting into the ocean
and ultimately melting) are still massive, increasing, and "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.”

\- Also, this article is from 2015. Here's a more recent analysis from 2018:
[https://www.nasa.gov/press-release/ramp-up-in-antarctic-
ice-...](https://www.nasa.gov/press-release/ramp-up-in-antarctic-ice-loss-
speeds-sea-level-rise/). You can even see the East Antarctica trend that the
2015 article talks about in this plot from the 2018 article:
[https://www.nasa.gov/sites/default/files/thumbnails/image/su...](https://www.nasa.gov/sites/default/files/thumbnails/image/supplemental_image_1-imbie2018-graph.jpg)

~~~
naushniki
Can you please elaborate for a non-scientist?

>ice sheet is gaining in mass due to the melting/compaction of snow

How does melting/compaction affect the mass?

~~~
crashedsnow
I assume it means snow melts, turns into water, then freezes again turning
into ice thereby increasing the mass of the ice sheet.

~~~
rolph
the density increases not the mass. the concentration of mass is increased
density. it is further evidence of melting.

~~~
bdamm
It reads to me like there's a distinction between ice and snow. Like the snow
isn't considered part of the ice or isn't able to be measured as part of the
ice until some compaction has happened, and the "snow" layer might be hundreds
of years worth of snow. That's the only way I can resolve the definitions with
the statements, and I'm hoping someone can more authoritatively describe the
paradox because I'm feeling unsatisfied.

~~~
rolph
there is also a distincion between the coastal ice sheets and the continental
interior ice and snow cap. the apparent paradox is caused by misrepresentative
interpretation of a report, by the author of the article.

the coastal ice shelf and continental interior are two distinct physical
systems.

isostatic rebound is a confound to the measurement of snow/ice accumulation
when change of altitude is corelated to snow deposition.

[http://rses.anu.edu.au/geodynamics/tregoning/7.pdf](http://rses.anu.edu.au/geodynamics/tregoning/7.pdf)
[PDF]

[https://www.worldatlas.com/articles/what-is-post-glacial-
reb...](https://www.worldatlas.com/articles/what-is-post-glacial-rebound.html)

BTW Re: " and I'm hoping someone can more authoritatively describe the paradox
because I'm feeling unsatisfied."

you wont get anymore of an authoritative take on it than discussing it with a
scientist, as you are currently doing right now.

------
mturmon
This is a several-years old study that has been controversial. Other results
using independent observations from mass-observing missions have come to very
different conclusions [1] [2].

One thing people should understand is that the method used in the linked
article is altimetry from radar, so you get a very accurate surface height,
but _the height is not a direct indicator of ice mass_ because of compression
of snow/ice, and rebound of the underlying continent.

It's really important to have some appreciation of the limitations of
measurement techniques, before jumping to conclusions from a single study.

[1] [https://grace.jpl.nasa.gov/resources/31/antarctic-ice-
loss-2...](https://grace.jpl.nasa.gov/resources/31/antarctic-ice-
loss-2002-2016/)

[2]
[https://news.ycombinator.com/item?id=19683895](https://news.ycombinator.com/item?id=19683895)

------
jcranmer
Some clarification on Antarctica:

There are roughly three regions in Antarctica. The Transantarctic Mountains
divide Antarctica into a really big East Antarctica and a smaller West
Antarctica. The two large ice sheets in Antarctica (Ross and Ronne) are in
West Antarctica. The tip edge of West Antarctica is the Antarctic Peninsula.

Everyone agrees that West Antarctica is losing ice. This is especially true of
the Antarctic Peninsula, which is basically under going complete collapse
(e.g., the Larsen Ice Shelf). It's unclear if the West Antarctic Ice Sheet is
merely declining or undergoing a more catastrophic collapse. The complete
collapse of this ice sheet is something that is included in the worst-case
scenarios for sea level rise.

East Antarctica is more difficult. The East Antarctic Ice Sheet contains far
more mass than West Antarctica--about 90% of the Antarctic Ice Sheet in total
is here. This ice sheet is roughly in balance, although the succession of
studies I've seen have ping-ponged between growing, stable, or declining,
which means you can find a study to support your viewpoint, whatever it may
be. Due to the sheer size of the ice sheet compared to everything else, small
uncertainties in the mass balance here basically dictates whether or not you
think Antarctica as a whole is gaining or losing ice mass.

------
machinecoffee
I thought this was well understood, and even expected by the models, since a
warming planet brings more precipitation in the air which then falls as snow
on the poles.

So the Antarctic is actually gaining mass on the higher ground, and the Arctic
during the winter months also.

The contrast is that during the warmer summer months, the Arctic is losing a
lot more than it gains over the year, so the global balance is negative -
which adds to sea level rises.

The other odd thing I never considered, but was (I think here?) mentioned, is
that as the mass of the Arctic decreases, it also presses down less on the
mantle, and so lifts higher out of the ocean, also displacing more sea.

I'm pretty sure there's a good explanation of this by Potholer54 on Youtube.

~~~
aetherson
Loss of ice in the Arctic doesn't contribute to sea level rise because the ice
in the Arctic floats, and melting an ice cube floating in water does not
change the water level.

(Ice on Greenland is a different matter, but Greenland is a lot smaller than
Antarctica.)

~~~
rolph
this is correct however its not all sea ice. permafrost is melting and running
off into the sea. the permafrost remnants, mostly silt subside but the
lithostrat[bedrock] rebounds like a slow trampoline. this causes rate of
permafrost melt and effluence to increase.

------
rolph
Mass is not density.

"They point out that the Antarctic ice sheet is gaining in mass due to the
melting/compaction of snow from the past 10,000 years"

    
    
      - i just copy pasta this from other posters comment for dialectic,
     this statement ^ indicates there is a change in density not mass.
    

If you watch a snow bank melt you will see an increased density, as individual
snow flakes [crystals] melt and lose air pockets making contiguous ice mass.

that means density increases.

Its still melting, Everybody!

~~~
jakeinspace
I interpreted that as meaning that the ice sheet is only defined as that water
which is in an icy state, not the snow that sits on top of it. If snow is
melting, refreezing, and becoming part of the ice sheet (not sitting above),
then the mass of the ice sheet is increasing.

~~~
rolph
yes the mass of ice sheet is increasing, on the continental interior.

this should not however be interpreted as a change in mass of coastal
icesheet. these are two different systems. separated by a mountain range.

------
dalbasal
Dunno what this means overall, just another reminder that this stuff is
complicated.

If climate change in Antarctica causes more snow/percipitation, ice will
accumulate there, even if average temperatures increase.

If I understand correctly, this isn't something new. It isn't clear if the
trend is accelerating or reversing. Ice always accumulates in Antarctica,
because whatever snow falls in the interior just sits there.

~~~
scriptkiddy
> Ice always accumulates in Antarctica, because whatever snow falls in the
> interior just sits there.

Not exactly. In most cases, the ice accumulates into glaciers and slowly flows
towards the sea.

As you can see from this relief map:
[https://commons.wikimedia.org/wiki/Category:Topographic_maps...](https://commons.wikimedia.org/wiki/Category:Topographic_maps_of_Antarctica#/media/File:Ant_hypso.png)
, Antarctica's interior is very mountinous and consistently a higher elevation
than it's edges. Gravity forces the compacted ice downhill. As the ice on the
mountains moves, so does all of the ice in it's way.

~~~
dalbasal
Does most of the continent "drain?" My understanding was that most/much of the
ice is not glacial.. which I understood as not moving.

~~~
scriptkiddy
> My understanding was that most/much of the ice is not glacial.. which I
> understood as not moving.

I haven't heard that. Could you link where you found that information?

------
sgroup
Newer 2018 article: [https://www.nasa.gov/press-release/ramp-up-in-antarctic-
ice-...](https://www.nasa.gov/press-release/ramp-up-in-antarctic-ice-loss-
speeds-sea-level-rise)

~~~
mturmon
Thank you for this link. The accompanying _Nature_ article is [1].

As I mentioned elsewhere in this thread, the study linked in the OP has been
in conflict with other measurements. The article you reference is one attempt
to synthesize the three measurements available (altimetry from SAR, surface
flow rate from imagery, and mass change from gravimetric observations) into a
complete picture.

[1]
[https://www.nature.com/articles/s41586-018-0179-y.epdf?autho...](https://www.nature.com/articles/s41586-018-0179-y.epdf?author_access_token=G6bM-
sEvNrsr_d3FPj8qjtRgN0jAjWel9jnR3ZoTv0PBEKqWHTwARrIrR4OxoHFdEh63arkDNi_bORoXuP_CQqP5K8MYc-
mJnNFT_QmTd-WnNN5Mp3ZqXQU1Cq6c0OT0JzMpvEGDRBCqqg_mMZ20Fg%3D%3D)

------
rolph

      Im looking at the terms and the grammer being used,
    

we have to put our bullshit detector hats on for this. its a controversial and
political subject, thus vulnerable to spin.

the considerations required for a realistic view are not impossible,
sophisticated, yes, but humanly understandable.

there are phrases and terms [ie ICE accumulation] that mask the real
description of the situation, and an appropriate model is not expounded upon.

ICE != snow , mass != density

ice accumulation != snow accumulation vice.versa.

------
fisherwithac
The previous HN discussion on this article:

[https://news.ycombinator.com/item?id=10487680](https://news.ycombinator.com/item?id=10487680)

