From Watts Up With That?

Guest Post by Willis Eschenbach

An online friend of mine alerted me to a curious change in the Greenland Ice Sheet. From the Danish Polar Portal, here are two of their graphics.

Figure 1. Surface Mass Balance (SMB), polar year 2022-2023.

The Polar Portal site says:

The blue curve shows the current season’s surface mass balance measured in gigatonnes (1 Gt is 1 billion tonnes and corresponds to 1 cubic kilometre of water).

The dark grey curve traces the mean value from the period 1981-2010.

The light grey band shows differences from year to year. For any calendar day, the band shows the range over the 30 years (in the period 1981-2010), however with the lowest and highest values for each day omitted.

And what is the surface mass balance (SMB) when it’s at home? Again from the Polar Portal.

The difference between snowfall and runoff is known as the SURFACE mass balance. It is always positive over the course of a year as not all fallen snow runs off the ice sheet again.

The surface mass balance is NOT identical to the TOTAL mass balance (i.e. overall gain or loss of the ice cap), which also includes the mass that is lost when glaciers calve off icebergs, the melting of glacier tongues as they come into contact with warm seawater and frictional and other effects at the bottom of the ice sheet.

From my perspective, the oddity is that despite the warmer-than-usual conditions of the North Atlantic for this time of year, the surface mass balance has grown more than at any time in the period 1981-2010. Go figure.

One thing you can depend on the weather to do, and that is, it won’t do what you depend on it to do …

However, this is just the surface mass balance (SMB). The total mass of the Greenland Ice Sheet continues to decline. And here’s where the graphic trickery comes into play. Folks like the Polar Portal are more than happy to show graphs of the cumulative loss of Greenland ice.

Figure 2. Polar Portal graph of ice loss since 2003

Looking for a longer dataset, here’s one I made, based on the British Antarctic Survey (IMBIE) data. Of course, I couldn’t make it all boring like most graphs. I like my graphs to be little works of art.

Figure 3. Cumulative ice mass loss since 1992, Greenland.

YIKES! At the rate that it’s falling, we’re clearly about to lose the Greenland Ice Cap entirely …

… however, this is just the loss. What kind of difference does this make to the total mass of the Greenland Ice Sheet? Figure 4 shows that change.

Figure 4. Change in total Greenland ice mass, 1992-2021.

Once again, it looks like we’re on the brink of a precipice.

However, there’s still one small detail to take into account. When we’re looking at totals of things, like changes in the total Greenland ice mass, it’s important that the vertical “Y” axis starts at zero. This is called a “zero-based” graph, and in the wonderful world of climate science, they’re pretty rare. Figure 5 shows why the alarmists don’t like them.

Figure 5. Zero-based graph of the change in total Greenland ice mass, 1992-2021. Note that this is the exact same data as in Figure 4 just above.

Whew! Looks like the catastrophe is averted. And in fact, if Greenland continues to lose ice at the current rate, it will all be gone around the year 14700AD.

[After comments, edited to add …] Are there times when non-zero-based graphs are appropriate? Absolutely. We need both kinds of graphs. But far too often these days, non-zero-based graphs are just used to frighten folks who are unaware of the relative sizes of things.

Puts me in mind of the old joke. A scientist says “The sun will go nova in five billion years”. One of the people in the audience stands up and says “What! That’s terrifying! What did you say?”

The scientist repeats his statement, and the man says “Oh, thank heavens. I figured I was gonna have to change my lifestyle. I thought you said five million years!”

Crazy world, crazy tune …

Regards to all, h/t to David Hart,

w.

Yeah, I know you’ve heard it before: When you comment, please quote the exact words you are referring to. It avoids all kinds of misunderstandings.