A new paper by Dr. Nicola Scafetta of Duke University examines the relationship of natural, solar-driven ocean oscillations such as the Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), and the North Atlantic Oscillation (NAO) to the changes in rate of sea level rise. He finds no correlation with atmospheric carbon dioxide or temperature.

Before I get into the Scafetta paper, here is some background.

Measuring sea level is more complicated than pounding a stake into a beach. Ideally, global sea level would be a rotating oblate ellipsoid of polar radius of 6365.752 km and equatorial radius of 6378.137 km in absence of any other forces. Gravity distorts this ideal shape to make it lumpy.

There are daily and seasonal variations, and storm surges in addition to the oscillations mentioned above. There are tectonic events: is the ocean rising or is the land sinking? Also, extraction of groundwater near coasts may cause the land to sink and present an apparent rise in sea level. All these confounding factors can produce a local rate of sea level change very different from global rate of change.

Since the end of the last glacial epoch, sea level has risen 120 meters (393 feet), about one meter per century. Sea level is still rising at the rate of 1- to 3mm per year, according to NOAA, about the thickness of one or two pennies.

As you can see from the figure, the rate of sea level rise has changed on broad time scales. Scafetta has found patterns of acceleration and deceleration of rise at much smaller time scales.

Scafetta studied six long-term tidal gauge records sited to represent all of the world’s oceans. He found the rate of sea level rise “…to be characterized by significant oscillations at the decadal and multidecadal scales up to about 110-year intervals. Within these scales both positive and negative accelerations are found if a record is sufficiently long. This result suggests that acceleration patterns in tide gauge records are mostly driven by the natural oscillations of the climate system. The volatility of the acceleration increases drastically at smaller scales such as at the bi-decadal ones.”

“Tide gauge accelerations oscillate significantly from positive to negative values mostly following the PDO, AMO and NAO oscillations. In particular, the influence of a large quasi 60–70 year natural oscillation is clearly demonstrated in these records.”

A conclusion from this paper has implications for climate model predictions: “at scales shorter than 100-years, the measured tide gauge accelerations are strongly driven by the natural oscillations of the climate system (e.g. PDO, AMO and NAO). At the smaller scales (e.g. at the decadal and bi-decadal scale) they are characterized by a large volatility due to significant decadal and bi-decadal climatic oscillations. Therefore, accelerations, as well as linear rates evaluated using a few decades of data (e.g. during the last 20-60 years) cannot be used for constructing reliable long-range projections of sea-level for the twenty first century.”

The cyclical nature of the rate of sea level rise, and its quite variable accelerations and decelerations at different time scales may explain why different researchers get different rate values. So, scary stories saying we are doomed because of acceleration in the rate of sea level rise, such as the ‘science fiction” stories linked below, should be taken with a grain of salt.

Reference: Scafetta, N., 2013, Multi-scale dynamical analysis (MSDA) of sea level records versus PDO, AMO, and NAO indexes, Climate Dynamics, DOI 10.1007/s00382-013-1771-3.

See the full paper here.

See also:

Science Fiction from the University of Arizona?

More science fiction from the University of Arizona

University of Arizona dances with sea level

Sea Level Rising?

Sea Level Rise in the South Pacific: None

Sea Level Rise Declining says EU

Obama parts the waters, sea level drops

Size matters in sea level studies

Sea level rising fast along American East Coast – or not

Tomorrow the University of Arizona will present some political theater.  In the evening, UA presents will feature a troupe from several South Pacific islands in a program titled  “Water is Rising.”  Preceding that on Friday afternoon is a discussion led by the UofA  Institute of the Environment titled “Vanishing Islands: Culture and Climate Change.” (See article here.)

It is unfortunate that what will probably be an entertaining evening of song and dance is being used as political propaganda posing Pacific islanders as victims of global warming-caused sea level rise that will inundate their homes.  Such propaganda is not new.  Back in 2009, Members of the Maldives’ Cabinet donned scuba gear and held a meeting under water in a publicity stunt about sea level rise.

The UA’s Institute of the Environment has also, in the past, issued alarmist articles about sea level rise flooding low-lying coastlines, see Science Fiction from the University of Arizona.

If you decide to go to the afternoon discussion, here are a few things you should know. Auckland University Professor Paul Kench has measured 27 islands where local sea levels have risen 120mm – an average of 2mm a year – over the past 60 years, and found that just four had diminished in size, the remaining 23 had either stayed the same or grown bigger, according to the research published in a scientific journal, Global and Planetary Change.

The Australian government has been monitoring sea level on Pacific islands with modern instruments since 1992.   In the case of Tuvalu, they state, “If   the   depression   of   the   1998   cyclone   is   ignored,  there   was   no   change   in   sea   level   at   Tuvalu between 1994 and 2009: 14 years. The recent slight fall would probably be related to the recent earthquake.”

Here is the Australian record of sea level for Tuvalu.  Other South Pacific islands show a similar record.

See also:

Sea Level Rising?

Sea Level Rise Declining says EU

Obama parts the waters, sea level drops

Size matters in sea level studies

During the presidential campaign, Barack Obama pompously declared that his presidency will be “the moment when the rise of the oceans began to slow and our planet began to heal.” (see statement on You-tube, link H/T to Marc Morano)

And lo! It has come to pass. The seas have receded from upon the land.

The European Space Agency’s Envisat monitoring, global sea level revealed a “two year long decline [in sea level] was continuing, at a rate of 5mm per year.”

NASA concurs. “While the rise of the global ocean has been remarkably steady for most of this time, every once in a while, sea level rise hits a speed bump. This past year, it’s been more like a pothole: between last summer and this one, global sea level actually fell by about a quarter of an inch, or half a centimeter.” But NASA blames it on La Niña rather than Obama power. There goes another Nobel prize.

The explanation from NASA:

Willis said that while 2010 began with a sizable El Niño, by year’s end, it was replaced by one of the strongest La Niñas in recent memory. This sudden shift in the Pacific changed rainfall patterns all across the globe, bringing massive floods to places like Australia and the Amazon basin, and drought to the southern United States.

Data from the NASA/German Aerospace Center’s twin Gravity Recovery and Climate Experiment (Grace) spacecraft provide a clear picture of how this extra rain piled onto the continents in the early parts of 2011. “By detecting where water is on the continents, Grace shows us how water moves around the planet,” says Steve Nerem, a sea level scientist at the University of Colorado in Boulder.

So where does all that extra water in Brazil and Australia come from? You guessed it–the ocean. Each year, huge amounts of water are evaporated from the ocean. While most of it falls right back into the ocean as rain, some of it falls over land. “This year, the continents got an extra dose of rain, so much so that global sea levels actually fell over most of the last year,” says Carmen Boening, a JPL oceanographer and climate scientist.

See also:

Sea Level Rising?