By Willis Eschenbach – Re-Blogged From WUWT
Today I saw some scary headlines. I post them up along with snippets of the stories. First, from the BBC:
Earth’s great ice sheets, Greenland and Antarctica, are now losing mass six times faster than they were in the 1990s thanks to warming conditions.
“That’s not a good news story,” said Prof Andrew Shepherd from the University of Leeds in the UK.
Next, from the NASA Jet Propulsion Laboratory (JPL)
The two regions have lost 6.4 trillion tons of ice in three decades; unabated, this rate of melting could cause flooding that affects hundreds of millions of people by 2100.
Finally, from LiveScience:
The rapid ice loss puts the world right on track for the ‘worst case’ climate scenario.
Hmmm, sez I, the dreaded “worst-case” climate scenario … so I went to find the data. The articles are in Nature magazine, links are here (paywalled, I got the DOI and used it over at SciHub to get the papers). The study is done by a group of scientists who are part of a project called the “ice sheet mass balance inter-comparison exercise” (IMBIE).
Here is their money graph regarding Antarctica:
Figure 1. From Mass balance of the Antarctic Ice Sheet from 1992 to 2017. The purple at the bottom is the overall total loss for Antarctica
And here’s the corresponding graph for Greenland:
Figure 2. From Mass balance of the Greenland Ice Sheet from 1992 to 2018. Click to expand. Dark blue is the overall total loss for Greenland
OK, both of those look scary enough.
So I downloaded the data. Kudos to the Imbie folks who did the study. The data’s all available on two Excel spreadsheets, freely available here. Figure 3 shows my graph of their data corresponding to the “Antarctica” part of Figure 1:
Figure 3. Cumulative ice mass loss, Antarctica. The photo is penguins on surreal ice.
And Figure 4 shows the corresponding data from Greenland:
Figure 4. Cumulative ice mass loss, Greenland. Note the different vertical scales. Greenland loses more ice than Antarctica.
YIKES! The ice loss looks like it’s falling off of an ice cliff …
So those agree with the IMBIE study, and they are both adequately terrifying.
Having seen that, I thought “how does this compare to the total ice mass in the Greenland and Antarctica ice sheets? Their ice volumes are not exactly known but are on the order of thirty million cubic kilometres in Antarctica and a tenth of that, three million cubic kilometres, in Greenland.
Now, one cubic kilometre is about 0.95 gigatonnes of ice. Using those figures, I added the monthly Greenland ice mass loss shown in Figure 4 to the total mass of the ice in Greenland. That gives me the monthly total amount of Greenland ice. Figure 5 shows that result.
Figure 5. Monthly change in Greenland ice mass as calculated but not graphed by the IMBIE team.
See the blue/black line across the top? Yep, that’s the change in Greenland ice. The net change is so small that you can’t really see it even in a quarter century plus of data. It’s about five-thousandths of one percent (0.005%) of the total Greenland ice mass per year … be still, my beating heart.
And here’s the corresponding plot for Antarctica:
Figure 6. Change in Antarctic ice mass as calculated but not graphed by the IMBIE team.
As before, the blue/black line across the top is indeed the change in the total ice mass of Antarctica. The thing is, all of that terrifying ice loss shown in Figure 3 represents a total loss of three ten-thousandths of one percent (0.0003%) of the Antarctic ice mass per year … lost in the noise.
Next, the media, and to a lesser extent the scientists, waste a bunch of ink hyperventilating about the effect on sea-level rise. They imply, but don’t state, that this is increasing the overall rate of sea-level rise. However, what they fail to note is that in fits and starts, the polar ice caps have been melting since we came out of the last glacial period … so the effect of polar meltwater is not new. Meltwater has been included in the sea level rise data for centuries. And as I’ve shown here, we’re not seeing any acceleration in the rate of sea-level rise in the longest and best tide gauge records we have.
Finally, here’s probably the biggest thing that the studies revealed. Figure 7 shows the monthly ice loss from Greenland and Antarctica combined.
Figure 7. Total combined monthly ice loss from Antarctica and Greenland
Notice anything curious about that chart? I mean, other than the fact it has a map of Greenland, Antarctica, and the US in the background?
Yep, you’re right. In 2011, it started going the other way. The great ice caps were losing more and more ice each year from 1992 to 2011. By 2011 they were losing about fifty gigatonnes of ice each month.
In that year, something changed. Since 2011, Antarctica and Greenland have recovered to where the loss is less than half of the maximum loss of fifty gigatonnes per month. Seems to me that things are getting colder, not warmer as all the headlines are shouting. Most recently the loss is only on the order of twenty gigatonnes per month.
And why is that? Why is the rate changing? Why is even the sign of the rate changing, from more ice lost each month to less ice lost each month? And why did that change occur nine years ago, and not seven years or eleven years ago?
Simple answer. We don’t know.
Oh, they tell you in the studies that it’s from “ocean-driven melting” or the “North Atlantic Oscillation” or ” atmospheric circulation favoured cooler conditions” or that the “spatial pattern of accelerating mass changes reflects the geography of NAO-driven shifts in atmospheric forcing” … but those are just mechanistic correlations and relations. When they say “ocean-driven melting”, they’re just saying that when the water is warmer the ice melts more. Which is trivially true, and doesn’t answer the simple question—why did the trend reverse nine years ago, and not eleven years ago, or seven years ago, or not at all?
We don’t know.