by Judith Curry
Since the early 1990s, sea level rose at a mean rate of ~3.1 mm yr−1. However, over the last decade a slowdown of this rate, of about 30%, has been recorded. – Cazenave et al.
For background on the topic of sea level rise, see these previous posts:
- PDO, ENSO and sea level rise
- 20th century mean global sea level rise
- Sea level rise discussion thread
An interesting new paper published by Nature Climate Change:
The rate of sea level rise
Anny Cazenave, Habib-Boubacar Dieng, Benoit Meyssignac, Karina von Schuckmann, Bertrand Decharme & Etienne Berthier
Abstract. Present-day sea-level rise is a major indicator of climate change. Since the early 1990s, sea level rose at a mean rate of ~3.1 mm yr−1. However, over the last decade a slowdown of this rate, of about 30%, has been recorded. It coincides with a plateau in Earth’s mean surface temperature evolution, known as the recent pause in warming. Here we present an analysis based on sea-level data from the altimetry record of the past ~20 years that separates interannual natural variability in sea level from the longer-term change probably related to anthropogenic global warming. The most prominent signature in the global mean sea level interannual variability is caused by El Niño–Southern Oscillation, through its impact on the global water cycle. We find that when correcting for interannual variability, the past decade’s slowdown of the global mean sea level disappears, leading to a similar rate of sea-level rise (of 3.3 ± 0.4 mm yr−1) during the first and second decade of the altimetry era. Our results confirm the need for quantifying and further removing from the climate records the short-term natural climate variability if one wants to extract the global warming signal.
Published in Nature Climate Change.
This paper is being spun in interesting ways. An article from Reporting Climate Science is titled Sea Level Rise Has Not Stalled Says Study. Reuters has a better article entitled Shifts in rainfall, not warming pause, slow sea level rise. Excerpts:
Sea level rise has been one of the clearest signs of climate change – water expands as it warms and parts of Greenland and Antarctica are thawing, along with glaciers from the Himalayas to the Alps.
But in a puzzle to climate scientists, the rate slowed to 2.4 millimetres (0.09 inch) a year from 2003 to 2011 from 3.4 mm from 1994-2002, heartening sceptics who doubt that deep cuts are needed in mankind’s rising greenhouse gas emissions.
Writing in the journal Nature Climate Change on Sunday, experts said the rate from 2003-2011 would have been 3.3 mm a year when excluding natural shifts led by an unusually high number of La Nina weather events that cool the surface of the Pacific Ocean and cause more rain over land.
In La Nina years, more rain fell away from oceans, including over the Amazon, the Congo basin and Australia, she said. It is unclear if climate change itself affects the frequency of La Ninas.
The apparent slowing of sea level rise coincided with what the U.N. panel of climate experts calls a hiatus in global warming at the Earth’s surface, when temperatures have risen less sharply despite record emissions of greenhouse gases.
“The slowdown in sea level rise … is due to natural variability in the climate and is not indicative of a slowdown in the effects of global warming,” Nature Climate Change said.
Many scientists suspect that the “missing heat” from a build-up greenhouse gases in the atmosphere is going into the deep oceans as part of natural variations in the climate.
But, because water expands as it warms, that theory had been hard to reconcile with the apparent slowdown in sea level rise.
Sea levels have risen almost 20 cms since 1900. The U.N. panel of climate experts expects an acceleration, with gains of between 26 and 82 cms over 100 years to the late 21st century.
Recall this figure from AR5 on 20th century sea level rise:
Consider the following statements from Cazenave regarding global sea level rise:
- the 20th century average is 2 mm/yr,
- observations from 1992-2002 are 3.4 mm/yr
- observations from 2003-2011 are 2.4 mm/yr
- when corrected for an abundance of La Ninas, sea level rise from 2003-2011 is ‘adjusted’ to 3.3 mm/yr
Rather than adjusting the period 2003-2011, instead adjust the period 1992-2002 for a surplus of El Ninos. Perhaps this would lower the sea level rise for this period to 2.5 mm/yr (or lower). I don’t think there is any objective/convincing way to filter out the effects of El Nino/La Nina. They seem to be an intrinsic part of sea level variations, as is the PDO/AMO on multidecadal time scales.
Can someone then tell me how you can infer that sea level rise is accelerating due to AGW, when compared with sea level rise for the first half of the 20th century?
It is clear that natural variability has dominated sea level rise during the 20th century, with changes in ocean heat content and changes in precipitation patterns.
Once again, the emerging best explanations for the ‘pause’ in global surface temperatures and the slow down in sea level rise bring into question the explanations for the rise in both in the last quarter of the 20th century. And makes the 21st century of sea level rise projections seem like unjustified arm waving.