Dangendorf et al. have made a new estimate of global sea level since the year 1900, based on data from tide gauges around the world. I’ve compared it (which I’ll call Dang) to the most trusted data set (in my opinion) from Church & White (which I’ll call CW), to the dataset I have criticized from Jevrejeva et al. (which I’ll call Jev), and to my own reconstruction (which I’ll call me) based on my own method of correcting for VLM (Vertical Land Movement). The first thing to note is that my own data doesn’t include proper area weighting, and can only be considered seriously flawed. But it is my own, so we’ll see how the new kid on the block compares to it, as well as to well-known data sets. Here’s the new data from Dang:
The method they use is a hybrid of two methods, one designed to get a better estimate of the trend, the other for better estimates of year-to-year fluctuations. I’m not sure yet how I feel about their methods, but I will say that when they compare their results to satellite data (since 1993 when we have both) the match is impressive. But this post isn’t about thier methods, it’s about their results.
The new data show a very steady trend, but with the same accelerations and decelerations as other data sets, albeit with different magnitudes and timings. Here are yearly averages for each of the four data sets based on tide gauges (aligned to have the same average value after 1993):
Although my own reconstruction has a larger noise level than the others, especially before 1950, its overall trend seems to match the new data from Dang, better than CW or Jev do.
I used a lowess smooth to estimate how the rate of sea level rise has changed over time, for each data set. Here’s what I got:
The most obvious “outlier” is the data from Jev. They show a high rate of sea level rise in the early-to-mid 20th century which is not shown by the others.
All reconstructions show a rate that is rising consistently since around 1990; a rise in the rate is acceleration. The biggest difference is that while the CW and Jev data show acceleration consistently since around 1990, the data from Dang and from me show it starting before that, in the 1960s.
In fact after 1960, the new data set very closely follows a constant acceleration curve, also known as a “parabola” or “quadratic.” For those who insist on such things, yes, it’s statistically significant. Way.
We’ve known for some time now that sea level rise is accelerating upward at ever-faster rates. This has been cofirmed since 1993 using satellite data, and appears also in the data from CW and from Jev. We now have evidence that sea level has been consistently accelerating since the 1960s.
The next step for me, is to look at individual tide gauge records with a focus on the period since 1960. It will be quite difficult to confirm acceleration even if present, for two reasons. First, the noise level is very high in tide gauge records. Second, restricting analysis to the time since 1960 leaves precious little data to work with (given the low signal-to-noise ratio), making identifying acceleration even more difficult.
I suspect that acceleration in tide gauge records is strong enough that some of them will show the signs clearly, despite the obstacles. The real challenge will be differentiating between “sudden acceleration in 1993” and “consisten acceleration since the 1960s.” It’s the kind of challenge which might be fun.
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