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Comment by chrisco255 | Hacker News Reader

http://polarportal.dk/en/greenland/surface-conditions/

Greenland Surface Mass Balance remains 10-20 gigatons above the 1981-2010 median (click Acc for accumulations).

What is unusual about this year, is how short the melt season was in general. Greenland normally melts off for nearly 3 months of the year. This year has seen only 5 weeks or so of melting. The ice has recovered significantly from 10 years ago when it experienced a record loss.

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As is very clearly stated in the page you linked to: "It does not include the mass that is lost when glaciers calve off icebergs and melt as they come into contact with warm seawater."

There has of course been no "recovery". You can see the Greenland Ice Sheet loss at: https://grace.jpl.nasa.gov/resources/30/greenland-ice-loss-2...

This one is a continual talking point for climate change deniers, and is corrected every time, but it still gets trotted out. I strongly advise you to actually learn something about this topic as I've seen you attempt to post on it before.

Between your link and mine, it shows that Greenland loses ~279 gigatons / year to calving and warm water contact. But so far this year, alone, according to the DMI it has gained ~400 gigatons in snow and ice(even after factoring for daily melt offs on the surface). And we're not even done with the year yet. That's a net gain.

No, your link shows SMB, my link shows the overall loss. There is no gain. Please learn what these numbers mean. I have had this conversation hundreds of times. You are completely wrong.

EDIT: If you don't believe me, simply email the folk at the Danish Arctic research institution (the link you provided). They will confirm.

Ok, I'll accept that and admit my mistake. Then tell me this, what has been the loss in SMB to calving and sea water contact this year? Where do we find that data, to see what the equation looks like for 2021 (since your data only goes to 2020)?

The figures for 2021 aren't available yet as the year isn't over. If you want more immediate data, please ask your elected representative to prioritise funding scientific research.

I'm curious why you're fixating on this year though? Do you think something has changed from the past 20 years? You do know the SMB has been mostly positive over that period, right?

If you notice, even in the GRACE data, the Mass loss was 3333 gigatons for that first decade (May 2002-Sep 2012). Which is an average of 333 gigatons of loss per year. And what you notice for this past decade is that the trend of loss is decelerating. 8 years of data to Aug 2020 show an additional loss of 1660 gigatons. Which is an average loss of 207 gigatons per year. That's a 37.8% reduction in ice loss and now, 2021 is shaping up to be one of the strongest ice mass gains in decades (whether a net loss or not, it will prove to contribute to deceleration this decade as well).

Tell me, what's your hypothesis, why is the trend decelerating?

> the Mass loss was 3333 gigatons for that first decade (May 2002-Sep 2012).

You conveniently used a month with an unusually sharp drop as your end of decade, which make me think I'm feeding a troll, but nevertheless:

The correct decade is May 2002 to April or May 2012, which gives you 272 gigatons per year as the average. There is pretty obvious seasonality in the data, so you can't just jump between seasons.

You could also use September 2002 to September 2012, if you insist on including the outlier month, which would work out out to 309 gigatons/year.

As the other commenter noted, my mistake to count 2002-2012, rather than 2003-2012, but the point still stands. There is a notable deceleration trend in the past decade and you can even visually inspect the chart to see it. After the record melt in 2012, you see significant deceleration. Note from 2016-2018 there was virtually no loss at all. 2020 was below average as well. And 2021 will be even further below average than that. It will show sideways or near sideways movement for this year.

Well, firstly you have a fence-post error: 2002-2012 is eleven data points. So, lets reverse your methodology. Let's look at 2002-2010 and then 2010-2020.

Now we see that in fact the trend is accelerating. I think that answers your question.

Ok, forgive me, it's hard to derive data from an MP4 file. I have to scroll the scrub bar and try to fixate it on the low points from each year. Ok, let's take 2003-2012, since 2002 was an incomplete year (the year GRACE launched).

Low point in 09-2003 was at -393GT from when GRACE launched. By 09-2012, it reached -3333GT. That's a 294 GT / year loss for the first decade. From 2012-2020, it has still gone down to 207GT/year loss (and will go lower when 2021 is factored for).

So no, it still does not answer my question. Clearly on the chart just visually inspecting it, you can see the deceleration in trend.

Back to the original question: what is causing the deceleration and given that 2021 continues strongly that deceleration trend, what do you expect the next decade holds?

Even if net gain is true, who cares about 1 year. The trend is more telling. It’s like saying the stock market is down this year so it will never go back up.

As I read it, your parent's link shows a net numbers.

It's not clear to me that it is net numbers, and it doesn't show 2021, which is the year we're talking about. I'd like to see the actual data and a study and not an MP4 file to be sure.

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