Headlines across Australia yesterday told us the dire news that a new study finds that “Sea level rising faster in past 20 years than in entire 20th century“. A new paper by Watson et al is driving the headlines, but underneath this Nature paper is a swamp of adjustments, an error larger than the signal, and the result disagrees with many other studies and almost all the raw measurements. Paper after paper kept showing that sea levels rates had slowed (e.g Chen showed deceleration from 2004, Cazenave said in the last decade sea-levels had slowed 30% (but argued post hoc adjustments could solve that). Beenstock used 1000 tide gauges and found no acceleration of sea levels over the last 50 years. A different researcher — Phil Watson, found that Australian sea levels rose faster before World War II then slowed down.)
Firstly, hundreds of tide gauges show sea level rising at about a third of the rate than satellites do. Worse, the original satellite raw data showed the same slow rise, until it was suddenly adjusted. The real scandal is that the rapidly rising trend was largely created by adjustments in the first place. These latest corrections just adjust down part of the rate which had been created by adjusting up. On top of all that, the long paleo-history of sea levels done by people like Nils-Axel M√∂rner show that the current rise is not unusual or unprecedented at all. Could it get more pointless? It can: the acceleration Watson et al found is so small it’s less than the errors. (See the graph below).
The conclusion of the paper is that instead of the sea levels rising at 3.2mm/yr as per the official satellite data, the are rising at 2.3mm/yr + 0.043mm/yr2 of acceleration. Over a century that means the projected sea level rise is revised downwards from 320mm to 251mm. That means sea level rise on current trends has dropped off the bottom end of any UNIPCC projection for sea level rise (AR5 WG1 SPM) for the period 2081-2100, as against 1985-2005. The likely range is between 260 and 820mm under all scenarios. The projection (mid-point 400mm) range is based on succeeding in cutting global emissions to near zero before 2100.
Tide gauges don’t agree with the satellites on sea level. The 68 most stable NOAA tide gauges around the world show about 1mm a year rise. Beenstock use a thousand tide gauges around the world and found the same rise of about 1mm/year. Nils-Axel M√∂rner has studied arrays of gauges as well but also used the opposite approach and found practically the single most stable beach in Northern Europe. He analyzed long records on all the beaches around it to figure out which way the whole area was tilting — again he found the change of the most stable point is about 1mm/year.
We’re analysing the decimal points of the acceleration of a trend that was largely created by adjustments in the first place. Why bother? The raw satellite data showed almost no rise at all from 1992-2002, and was post hoc adjusted up from less than 1mm to 2.3mm/yr (Aviso, 2003). And the raw low rate was skewed high by the El Nino in 1997. These adjusted figures have been used to generate thousands of headlines about how sea levels are rising faster after 1992. (Anyone going to retract those headlines?) The European satellite data was also adjusted up. Nils-Axel M√∂rner has described the whole sordid process of sea level adjustments in detail. Knowing this puts the ABC version is a new light. Christopher Watson, lead author, “said the study suggested satellites marginally overestimated the rate of sea level rise in the first six years and that distorted the long-term picture.” He didn’t mention that it was the overestimate of the underestimate and all these numbers were subject to change, post hoc, ad hoc, as the wind blows…
Sea levels are always changing and past changes were often larger.
- Past changes were larger in the Maldives (M√∂rner, 2007); In Connecticut (van de Plassche, 2000),; SW Sweden ‚Äì Kattegatt Sea region (M√∂rner, 1971, 1980); In the Kattegatt and the Baltic (√Öse, 1970; M√∂rner, 1980, 1999; Ambrosiani, 1984; Hansen et al., 2012). Other sites (e.g. Pirazzoli, 1991). [See the link above for the full references].
- White et al showed seas around Australia were rising at about the same speed during the depression era as they are now.
The rate since 2002 is slowing despite the massive emissions of CO2: The new adjustments on adjustments bring the 1992 ‚Äì 2012 rate down (did the ABC tell you that?). This changes the curve, and creates a weak acceleration that was not there before.This also creates new headlines of “acceleration”. At some point in the future, today’s measurements will be adjusted down to create more headlines of “acceleration”. Rinse Repeat Recycle.
If tide gauges were good enough to figure out the rate of acceleration from 1900 ‚Äì 1992, why are they wrong as soon as the satellites start operating? Does anyone think we should compare highly adjustified satellite data to tide gauges if there are continuous tide gauge records over the same period? Its like a tree-ring spliced to a thermometer: Good PR, bad science.
The acceleration is so small it’s less than the errors. (Be afraid, it’s accelerating at 0.043 +/- 0.058 mm/yr2.) Normal scientists don’t get excited at this. They don’t issue press releases.