I’ve read the written testimony from Judith Curry before a recent meeting of the Environment and Public Works committee of the U.S. Senate. There’s plenty of stuff that gobsmacked me, but let me tell you what astounded me most on my very first reading.
Global sea level has been rising for the past several thousand years. The key issue is whether the rate of sea level rise is accelerating owing to anthropogenic global warming.
I almost can’t believe that she actually said that.
Let me repeat: I almost can’t believe she actually said that. To a U.S. Senate committee.
There’s considerable evidence that sea level has risen over the last few thousand years. Some of you may be familiar with this graph (from Wikipedia, prepared by Robert Rohde of the “Berkeley team” of which Curry is a member):
It shows sea level estimates throughout the holocene (since 9000 years ago). It seems to me that these data don’t make it certain, but do make it very likely sea level has risen (or at least, not fallen) throughout the holocene. But what’s really important is that it enables us to set some limits on how fast sea level has risen in that time.
Since the year 1900, sea level has risen at an average rate of 1.6 mm/yr according to the global sea level data from Church & White, 1.9 mm/yr using the data from Jevrejeva et al., 1.7 mm/yr according to the Ray & Douglas data. Just for the sake of argument, let’s say between 1.5 and 2 mm/yr over the last century plus.
Has it been going that fast — or even close — for the past several thousand years? Let’s add some lines to the graph, representing what sea level would have been if it had been steady, or had been rising at 0.5 mm/yr, 1 mm/yr, 1.5 mm/yr, or 2 mm/yr:
According to the data, it’s possible — but very unlikely — that sea level rose at an average rate of 0.5 mm/yr throughout the last 6,000 years. But it’s not really possible for the rate to have been as high as 1 mm/yr. As for “between 1.5 and 2 mm/yr,” I believe the correct mathematical nomenclature would be “No way.”
It’s obvious, to anybody who knows what the data say, that the rate over the last century plus has been significantly higher than the rate over the past several thousand years. Obvious.
We could also focus on a more recent time span, the last 2,000 years. I managed to find a reconstruction of sea level at North Carolina covering that time period by Kemp et al. (2011, PNAS, 108(27), 11017-11022, doi:10.1073/pnas.1015619108).
They provide a smoothed time series (shown above), and the data on which it’s based, so of course I took the data and smoothed it myself in order to estimate the rate of sea level rise:
Holy high tide, Batman! A hockey stick!
It wasn’t doing much until about the year 1900, but since then it has taken off like a bat out of hell. In other words, the rate increased — which is what we math geeks call “acceleration.” Mentioning “the past several thousand years” highlights the dramatic nature of the change, unless of course all you say about the past several thousand years is that “Sea level has been rising,” you say nothing about how fast compared to how fast it’s rising now, and trust that your audience hasn’t got a clue (which for members of the U.S. Senate is a pretty safe bet).
The fact that “Global sea level has been rising for the past several thousand years” is about as relevant to this issue as the fact that “People died of lung cancer long before there were cigarettes” is to the issue of smoking and health. My opinion: saying that without even mentioning the evidence about the last century’s dramatic increase in the rate is either ignorance on parade, or the kind of mendacity we might refer to as “true lies.”