By adjusting satellite data for a major volcanic eruption and natural ocean oscillations, global sea level rise has accelerated in the last 25 years, according to a study released Monday.
The study’s authors say their work shows that manmade global warming is increasing sea level by an average of 0.08 millimeters per year, mainly due to melting ice caps and the thermal expansion of oceans.
“This acceleration, driven mainly by accelerated melting in Greenland and Antarctica, has the potential to double the total sea level rise by 2100 as compared to projections that assume a constant rate — to more than 60 centimeters instead of about 30,” lead author Steve Nerem, a fellow at the Cooperative Institute for Research in Environmental Sciences, said in a statement.
“And this is almost certainly a conservative estimate,” Nerem said of the study, which was published in the Proceedings of the National Academy of Sciences.
The study is already being touted as validation of claims made by the Intergovernmental Panel on Climate Change, NASA and other organizations. Those groups claimed warming had accelerated sea level rise in recent years.
Climate models project sea level rise to accelerate from melting ice caps and thermal expansion, but so far, the in-satellite derived mapping of global sea level makes it hard to discern any acceleration.
Natural ocean cycles, like El Ninos and La Ninas, can play a big role in increasing or decreasing sea level rise every year. Scientists also say the 1993 eruption of Mount Pinatubo influenced sea level rise.
Thus, Nerem and his colleagues “tried to adjust the [global mean sea level] measurements for as many natural interannual and decadal effects as we can to try to isolate the longer-term, potentially anthropogenic, acceleration,” according to their study.
Correcting for Pinatubo’s eruption increased annual sea level rise 0.02 millimeters, and correcting for El Niño Southern Oscillation (ENSO) reduced the acceleration by 0.03 millimeters.
“Ideally, we have removed the ENSO effects from our data,” Nerem told The Daily Caller News Foundation.
Once those are removed, Nerem’s study found that sea level rise on average has accelerated by 0.08 millimeters per year. But the reported acceleration is well within the margin of error of the annual sea level rise of 3 millimeters per year.
TheDCNF asked Nerem about this, to which he responded that “there are errors that mainly affect the rate and not the acceleration.”
“The rate of sea level rise was found to be 3 ± 0.4 mm/year,” Nerem said via email. “The acceleration is 0.084 ± 0.025 mm/year^2. We use BOTH of these numbers to extrapolate sea level rise to 2100 – ~ 65 ± 12 cm.”
The projection of 65 centimeters, or a little over 2 feet, of sea level rise comes using the IPCC’s “worst case” global warming scenario. Called RCP8.5, that model projects as much as 9 degrees Fahrenheit of warming by 2100.
Experts are increasingly questioning the usefulness of RCP 8.5 as a plausible global warming scenario because of the assumptions it makes about coal-fired power use. A recent study found “RCP8.5 and other ‘business-as-usual scenarios’ consistent with high CO2 forcing from vast future coal combustion are exceptionally unlikely.”
On another note, even with the ENSO corrections in the study, huge spikes in sea level rise appear in the adjusted satellite data during years with incredibly strong El Nino warming events.
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