Wednesday, December 10, 2014

Papers Find No Change in Rate of Sea Level Rise

A recent paper in JGR-Oceans finds no acceleration in sea-level for the period 1900-2009.

Wenzel and Schröter found an average sea level rise of +1.8 mm/yr for this interval, and up to +6 mm/yr in the western Pacific and Indian Ocean. To determine global acceleration they fit a parabola to the data; the global acceleration was positive but not statistically significant (the error was about twice the acceleration's value of +0.0042 mm/yr2), with some local values around -0.1 mm/yr2 in the Indian Ocean to +0.1 mm/yr2 in the western tropical Pacific.

They write:


Another paper finds that sea level is rising 1.5 mm/yr due to ocean mass addition (that is, melting of land ice) for 1996–2006, and finds no recent acceleration, saying their results suggest
"...the global trend rate from 1996 to 2006 versus 2003 to 2013 has not changed significantly, or at least not outside our error estimates."
A few weeks ago I looked at Aviso's satellite sea level data, which covers 1993-present, and found a negative acceleration of -0.012 ± 0.010 mm/yr2. It was once positive (though barely 20 years long), but got clobbered by the generally La Nina conditions since the mid-2000s. But the acceleration is increasing (becoming less negative), and will probably turn positive in the next 1-2 years:


5 comments:

David Sanger said...

Or in other words, sea level is still rising, but not necessarily faster and faster every year.

And in the case of Aviso it started rising a bit less each year but that slowdown is lessening.

David Appell said...

Yes.

tonylearns said...

i have read that SLR was around 3mm/ year and that that was an acceleration form 20th century of 1.5

Mark said...

Let's be clear, the first paper looks at global sea level rise over the 20th century from tide gauge data and finds a mean rate of 1.77 mm/yr and finds an acceleration that is not statistically significant. The finding differs from some other papers (eg. Church and White 2011) that do find a 20th century acceleration. The differences are probably related to the different methods of projecting data from tide gauges to the entire ocean.

The remaining papers take the near-global satellite altimeter (eg. Aviso) data set since 1993. The rise indicated by this data is large than the 20th century average at around 3 mm/yr. But there is no sign of acceleration within these 20 or so years.

Acceleration (or lack thereof) within the last 20 or so years is not the same as acceleration (or lack thereof) during the 20th century.

To a simple-minded person such as me, the fact that the rise over the last 20 years (3 mm/yr) is higher than the 20th century mean (1.7 mm/yr) is itself an indicator of acceleration.

Frank1123581321 said...

Analyzing noisy data to determine if SLR is accelerating is a waste of time - unless you first ask: "How much acceleration would be needed to produce catastrophic levels of SLR this century?"

Sea level is rising at somewhere between 1 and 2 cm/decade. If the rate averages 2 cm for this decade, 3 cm the following decade, 4 cm the following, etc.; that would be an acceleration of 1 cm/decade/decade. That is 15 cm (6 inches) of SLR for 2001-2050 and 55 cm (22 inches) of SLR for the century. (SLR last century was about 9 inches.) 0.5m of SLR is about the central estimate for the IPCC's projections and less than the high end for RCP8.5.

Therefore, as long as we aren't seeing SLR accelerating at a rate of 1 cm/decade/decade, we aren't on a path towards reaching even the IPCC's estimates, much less the alarmists estimates of 1 m or more.

Regional variation in SLR are caused by weather (wind and pressure) and subsidence. Subsidence is a local issue unrelated to AGW. Changes in weather patterns may temporarily enhance or suppress SLR in some regions, but there in no reason to expect those trends to continue. The real issue is global SLR.

PS. Discussing SLR in units of cm/decade or inches/decade produces numbers that are simpler to work with and more tangible for readers. 0.1 mm/yr2 is 1 cm/decade/decade. Many know that daily tides are several feet in height. Most have experienced changes at one location over one or a few decades.