Today’s junk science comes from the Guardian (polar bear and all!):
Melting ice sheets in Greenland and Antarctica are speeding up the already fast pace of sea level rise, new satellite data shows.
At the current rate, the world’s oceans will be on average at least 60cm (2ft) higher by the end of the century, according to research published in Monday’s Proceedings of the National Academies of Sciences.
Based on 25 years of satellite data, however, the research shows that the pace has quickened. It confirms scientists’ computer simulations and is in line with predictions from the UN, which releases regular climate change reports.
This is the paper referred to:
Satellite altimetry has shown that global mean sea level has been rising at a rate of ∼3 ± 0.4 mm/y since 1993. Using the altimeter record coupled with careful consideration of interannual and decadal variability as well as potential instrument errors, we show that this rate is accelerating at 0.084 ± 0.025 mm/y2, which agrees well with climate model projections. If sea level continues to change at this rate and acceleration, sea-level rise by 2100 (∼65 cm) will be more than double the amount if the rate was constant at 3 mm/y.
Using a 25-y time series of precision satellite altimeter data from TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3, we estimate the climate-change-driven acceleration of global mean sea level over the last 25 y to be 0.084 ± 0.025 mm/y2. Coupled with the average climate-change–driven rate of sea level rise over these same 25 y of 2.9 mm/y, simple extrapolation of the quadratic implies global mean sea level could rise 65 ± 12 cm by 2100 compared with 2005, roughly in agreement with the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (AR5) model projections.
GMSL from the adjusted processing of ref. 15 (blue) and after removing an estimate for the impacts of the eruption of Mount Pinatubo (12) (red), and after also removing the influence of ENSO (green), fit with a quadratic (black). The acceleration (0.084 mm/y2) is twice the quadratic coefficient.
Previous studies, such as this one from NOAA, had found that the rate of acceleration had actually decreased since the start of the satellite era in 1993.
What this new study has done is assume that Pinatubo had artificially slowed sea level rise prior to 1993, as this paper explained in 2016:
Global mean sea level rise estimated from satellite altimetry provides a strong constraint on climate variability and change and is expected to accelerate as the rates of both ocean warming and cryospheric mass loss increase over time.
In stark contrast to this expectation however, current altimeter products show the rate of sea level rise to have decreased from the first to second decades of the altimeter era.
Here, a combined analysis of altimeter data and specially designed climate model simulations shows the 1991 eruption of Mt Pinatubo to likely have masked the acceleration that would have otherwise occurred.
This masking arose largely from a recovery in ocean heat content through the mid to late 1990s subsequent to major heat content reductions in the years following the eruption.
In other words, the start of satellite measurements coincided with artificially low sea levels.
The new paper from Nerem at al makes adjustments to sea levels to allow for this effect, allowing them to claim that sea level rise would really have been less in the first decade if Pinatubo had not occurred.
But here’s the real point, one I have made in the past. Because of the Pinatubo effect, the claimed rate of rise since 1993 is artificially high.
It is claimed that sea levels have risen by 3.1mm/year since 1993, according to satellites.
Nerem’s paper reckons that if we take Pinatubo out of the equation, the rise would fall from 3.1mm to 2.9mm.
But both of these numbers include 0.3mm for glacial isostatic adjustment (GIA), a recognition of the fact that ocean bottoms have been sinking since the end of the ice age. This of course has nothing at all to do with sea level rise, as measured at coastal sites.
In other words, after taking out the effect of Pinatubo, the rate of sea level rise would only be 2.6mm/year.
Looking at the long term trend from tidal gauges, there is nothing remotely unusual about rate of rise.
Nerem et al claim that if sea level continues to change at this rate and acceleration, sea-level rise by 2100 (∼65 cm or 26 in) will be more than double the amount if the rate was constant at 3 mm/y.
This is clearly nonsensical and unscientific. There is not the slightest evidence that a slight acceleration measured over the last two decades will continue. Indeed, all of the past data shows that the rate accelerates and subsides regularly.
For sea levels to rise by 65cm (26 in) by 2100 would mean an average annual rise of 7.8mm (0.307 in), three times the current rate.
If you accelerate your car from 0 to 60mph in 10 seconds, and assume that such acceleration will continue, it would not be long before you were driving at light speed. (My calculator says about 8 hours!)
Yet this is essentially the same logic used by Nerem.
To call it junk science is being too generous.
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