By Climate Guest Blogger on Apr 3, 2013 at 11:49 am
You may recall a couple years ago the climate disinformers trumpeted the (very) short-term slowdown in sea level rise. We can hardly wait for their posts on the recent speed up — JR.
Figure 1: Mean sea level (in centimetres) since 1993 obtained by satellite altimetry observations. Annual and semi-annual signals have been removed to reveal the long-term trend. The glacial isostatic adjustment (GIA) of 0.3mm per year is added to account for the slumping of ocean basins. Image from the AVISO website.
By Rob Painting, via Skeptical Science
The Earth is warming which is driving the ongoing thermal expansion of sea water and the melt of land-based ice. Both processes are raising sea level, but superimposed upon this long-term sea level rise are what scientists at NASA JPL (Jet Propulsion Lab) have coined, “potholes and speed bumps on the road to higher seas“. (See their follow-up paper – The 2011 La Niña: So strong, the oceans fell, Boening 2012).
Since mid-2011 a giant “speed bump” has been encountered. In roughly the last two years the global oceans have risen approximately 20 millimetres (mm), or 10 mm per year. This is over three times the rate of sea level rise during the time of satellite-based observations (currently 3.18 mm per year), from 1993 to the present.
So does this mean land-based ice is undergoing a remarkably abrupt period of disintegration? While possible, it’s probably not the reason for the giant speed bump.
Pot Holes and Speed Bumps
The largest contributor to the year-to-year (short-term) fluctuation in sea level is the temporary exchange of water mass between the land and ocean. This land-ocean exchange of water is coupled to the natural Pacific Ocean phenomenon called the El Niño Southern Oscillation (ENSO) – which affects weather on a global scale. (See Ngo-Duc 2005, Nerem 2010, Llovel 2011, Cazenave 2012 & Boening 2012 – linked to above):
Figure 2 – Global sea level with the long-term rise (trend) removed. Sea level (blue line), compared to the Multivariate ENSO Index (a measure of the state and scale of ENSO) in red. Negative values represent the La Niña (cold) phase, and positive values the El Niño (warm) phase. Image adapted from the University of Colorado (CU) Sea Level Research Group.
The ocean, through strong evaporation in the tropics, is the source of the water that is being exchanged. Each occurrence of ENSO has its own unique set of characteristics, but La Niña is typically (although not always) associated with greater-than-normal rainfall and snow over land, and a consequent sharp, but temporary, fall in global sea level (pot holes) as the continents soak up the extra water. With El Niño we often see greater-than-normal rainfall and snow concentrated over the oceans. Combined with the drainage of water back into the oceans, this causes an abrupt, but temporary, rise in sea level (speed bumps)……(read more).