Sea level isn’t just rising, it is accelerating. It did so during the 20th century, and has done so even more quite recently. ABC news reported the story, based on just-published research (Nerem et al. 2018), that the latest satellite data now show it plainly. The authors of the new study conclude:
When taken with a rate of sea-level rise of 2.9 ± 0.4 mm/y (epoch 2005.0), the extrapolation of the quadratic gives 654 ± 119 mm of sea-level rise by 2100 relative to 2005, which is similar to the processed-based model projections of sea level for representative concentration pathways 8.5 in the IPCC Fifth Assessment Report. Stated alternatively, the observed acceleration will more than double the amount of sea-level rise by 2100 compared with the current rate of sea-level rise continuing unchanged.
They did more than confirm acceleration of sea level rise; they estimated how much of it is because of man-made climate change. To do so with precision, you have to account for the changes due to other factors, in particular terrestrial water storage (TWS), and volcanic eruptions.
Variations of TWS are largely due to changes in precipitation patterns brought about by the el Niño southern oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Therefore they estimated, and removed, the influence of ENSO/PDO as well as the major volcanic eruption of Mt. Pinatubo. Without those adjustments, the estimated acceleration is 0.096 mm/y2, but when they are accounted for it reduces to 0.084 mm/y2. They also included in their estimate of the uncertainty changes in decadal variations of the cryosphere, the influence of variations in precipitable water on the satellite data, and the rate of thermosteric (due to temperature) sea level rise. The net result is that the uncertainty in the acceleration is about 0.025 mm/y2. This is about the same as my own estimate of the uncertainty based on the raw data alone, but that’s because my estimate is higher due to modelling the noise as an ARMA(1,1) process rather than an AR(1) process as did the authors.
Here’s the latest from the sea level site at the University of Colorado:
I’ve already removed the seasonal cycle. I also added a smooth fit (modified lowess) to highlight the overall pattern. The acceleration is evident. Here’s my estimate of the rate of sea level rise during the satellite era:
The average rate (from satellite data) is 3.1 mm/y, but the present rate is closer to 4.8 mm/y. That’s a substantial increase — a 50% increase.
My estimates are based on the raw data, and do not remove the estimated influence of ENSO/PDO or the Mt. Pinatubo volcano. That’s why the rate seems to “level off” at the end, a behavior which is due to the 2015/2016 el Niño. With that influence removed, sea level rise is still accelerating.
Another possible source of uncertainty in their estimated rate of sea level rise is that they use a quadratic function to estimate its changes. It’s clear to me that the pattern is more complicated; a quadratic (fit to the raw data) estimates the rate of sea level rise now at 4.3 mm/y, but a more realistic fit gives a higher rate.
Extrapolating the quadratic to the end of the century is fraught with uncertainty and shouldn’t be taken as a realistic forecast, but it does provide a reasonable lower bound on this century’s imminent sea level rise. That’s because, as the authors say,
If sea level begins changing more rapidly, for example due to rapid changes in ice sheet dynamics, then this simple extrapolation will likely represent a conservative lower bound on future sea-level change. In contrast, few potential processes exist to suggest that this estimate is too high.
There are many sources for sea level rise, but the likely dominant causes of the recent acceleration are increased melt from the Greenland and Antarctic ice sheets:
The consequences for humanity, especially the billions of people who live in coastal regions, will be profound. The cost to society, both economic and otherwise, will be astounding. We need to do everything we can to limit future global warming, especially to avoid those “rapid changes in ice sheet dynamics” that could make what is already a terrible situation seem like the “good old days.”
While real scientists, doing their best to give us the most precise estimates possible, are warning us of the danger, climate deniers continue to spread fear, uncertainty, and doubt based on bullshit. Witness a recent post at WUWT in which Philip Lloyd actually expresses doubt that present sea level rise “is partly due to heating of the oceans and their consequent expansion.” He tries to show that the thermal expansion of the ocean is negligible, by characterizing global sea level rise with a single tide gauge record (from Wismar, Germany), comparing straight-line fits for some time spans (1910-1950 and 1980-2015) to the long-term straight line fit, then declaring “… both of which are barely distinguishable from the long-term regression shown by the black line.” It’s only “barely distinguishable” to climate deniers and Stevie Wonder.
Continued denial of sea level rise acceleration can cost more than money and property, it can cost lives. When storms do come, when hurricanes strike, flooding can be deadly, and every inch of sea level rise makes whatever flooding happens much worse, makes the death toll higher. Denial makes us less prepared to reduce the future impact and less prepared to deal with what comes.
That’s why climate-denier politicians in the U.S. like EPA head Scott Pruitt and president Donald “grab ’em by the pussy” Trump have got to go. To all Americans: get out and vote! Vote them into oblivion, and all the climate-denier politicians (almost entirely Republicans) who either conspire with their denial, or tolerate it. The only thing necessary for the triumph of evil is for good men to do nothing.
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