A new study claims sea level rise has accelerated globally, in sharp contrast to previous estimates showing that sea level rise has slowed for the past decade because of natural variability.
The only problem with this claim is that the study’s own data seems to refute it, according to scientist Dr. David Whitehouse of the Global Warming Policy Foundation. The study itself notes that its estimates of a sea level acceleration aren’t “significantly different from zero.”
“To reach such an important conclusion based on such statistics is not supportable, in my opinion,” Whitehouse wrote.
The study’s author, however, argues otherwise.
“Our study confirms that the rate of sea level rise over the satellite era (the last ~22 years) is clearly larger than the many previously reported rates of sea level rise determined over the full 20th Century,” Christopher Watson, a scientist at the University of Tasmania and the study’s lead author, told The Daily Caller News Foundation.
“Over this longer period, sea level has accelerated,” Watson said.
Scientists have argued that sea level rise has accelerated since 1993 in conjunction with increasing ice loss from Greenland and Antarctica. But previous estimates of global sea level indicated a slight deceleration.
In contrast, Watson’s study used “improved” satellite measurements and found “an acceleration in sea-level rise.” Watson’s new found acceleration in sea level rise, however, is not statistically different from zero, which is the crux of Whitehouse’s criticism.
But Watson told TheDCNF the “statistically significant” difference claimed by the study is the difference between the previously measured deceleration in sea level rise versus the newly claimed acceleration in sea level rise.
“So it is the difference between the two that we find most striking, and provides the necessary context when interpreting these results,” Watson said.
Watson’s study put the acceleration of sea level rise at +0.041 millimeters per year squared in the past two decades, compared to a deceleration rate of -0.057 millimeters per year squared. But the margin of error of these estimates is +/- 0.057 millimeters per year squared, meaning neither of these figures is statistically different from zero.
In the study, Watson and his colleagues even note that “[n]either of these figures is significantly different from zero.” But the researchers argue that “the revised estimate is significantly different from the earlier estimate derived from data unadjusted for the effects of bias drift.”
“You would think that would be the end of the matter as both results are statistically unimportant being not statistically different from zero,” Whitehouse rebutted. “But you would be wrong.”
“The researchers take the view that there is a difference between the before and after results because the initial figure is smaller than zero (but not statistically different from it) and the corrected figure is larger than zero (but still not statistically different from it) so that means there has been an acceleration!” Whitehouse added.
Sea levels have been rising since the end of the last ice age, but in the last century scientific evidence suggests the rate of sea level rise has increased. Experts have argued that sea levels have risen even faster in the past two decades because of glacial melt from global warming.
But there are lots of problems in measuring sea level rise. Tidal gauges, for example, are only present on the edge of the ocean and are susceptible to the vertical movement of the land from surface relaxation or ice melt. Watson’s study used satellite data to take this vertical movement into account and more accurately estimate sea level rise.
“Personally I have never been very enthusiastic about claims of changes in the rate of sea-level rise,” Whitehouse wrote. “Too much noise combined with time spans that are clearly too short to be meaningful have always dissuaded me.”
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