Guest Post by Willis Eschenbach
I came across this beautiful example of chartsmanship today in a Chris Mooney post of raw, pure, visceral alarmism, it’s a gem. It’s from the Mother Jones website and comes with the lovely headline “Humans Have Already Set in Motion 69 Feet of Sea Level Rise”. I do love the claims that something is “set in motion”, it’s scientific cowardice to make that claim, it’s totally impossible to falsify. I could claim that Vladimir Putin has “already set in motion” the next financial meltdown … could you falsify my claim? In any case, Mooney’s post shows the terribly worrying loss of ice from Greenland, from a study by Jason Box
Figure 1. Cumulative loss of ice area in Greenland. As you can see, Greenland is toast … it’s losing well over a hundred square kilometres of ice per year, and the chart shows it heading to the cellar, looks like a total meltdown coming up.
So … what actually is happening with Greenland? To figure that out, we need another chart, the real chart—the chart of the post 2000 ice loss, and what might happen over say the next century if it continues losing over a hundred cubic kilometres of ice per year.
To do that, we have to start by finding out the area of the ice sheet that covers Greenland. As usual, there are various estimates. The Physics Hypertextbook is great for this kind of thing because it gives a variety of estimates from various authors. They range from a low end of 1.7 million square kilometres to a high of 2.2 million square km. I’ll take an average of 1.9 million square km.
So … here is the effect on the Greenland ice cap that a continued loss of -131.5 km2 per year every year until 2100 would have:
Figure 2. Effect of -131.5 km2/yr ice loss on the ≈ two million square kilometres of the Greenland ice cap.
Pretty scary, huh? By the year 2100, if it continues losing ice at the rate Jason Box claims above, -131.5 km2 per year, the total ice area of Greenland will have gone from 1.90 million square km all the way down to … well, to two decimals of accuracy, by the year 2100 the ice will be down to 1.90 million square kilometres …
Gotta love those charts … in any case, let us consider the headline, “Humans Have Already Set in Motion 69 Feet of Sea Level Rise”. I suppose it is true IF we are the cause and IF the decline continues, both of which seem doubtful. Assuming all that were true, at the current rate of -131.5 km2 of ice loss per year, Greenland will be ice-free fairly soon, in only … well … 1,900,000 km2 ice area / 131.5 km2 per year annual loss ≈ 14,500 years from now …
Rats … I guess it’s a bit early to be looking for a nice piece of land for my Greenland vineyard …
[UPDATE] Well, it is inevitably true that what I think is clear actually isn’t … no surprise there. From the comments:
February 7, 2013 at 8:28 am
Um, you know… “Greenland marine-terminating glacier area changes” and “cumulative loss of ice area in Greenland” are two a bit different things. Or rather, very different things.
Maybe you should take one more look at what exactly are you doing here.
I completely agree with the conclusion that the alarmism is unsubstantiated in this case. But the way you used to get there is not valid.
I agree with you, Kasuha, that “Greenland marine-terminating glacier area changes” and “cumulative loss of ice area in Greenland” are two very different things. That’s the problem. Mooney is using a chart of the changes in the area of the discharge of the Greenland ice into the ocean as the screaming visual for a claim that we’ve set in motion a 69 foot sea level rise … and the two have absolutely nothing to do with each other.
I didn’t know how to best discuss that kind of lunacy, so I took the path of saying well, suppose Boxes’ results were correct and it actually made a difference regarding the ice area, what difference would it make? I was not attempting to model the entire ice loss of Greenland, as I’ve been through that question in some detail already …
Perhaps there are better ways to get the point across, as you point out … that’s the one I picked.