Guest post by David Archibald

This is a little bit amusing. In February, I had a post on the solar – sea level relationship which quantified the sea level fall to come to the end of Solar Cycle 25:

http://wattsupwiththat.com/2012/02/03/quantifying-sea-level-fall/

The site “Skeptical Science” has to date carried two pieces in response to that February post: http://www.skepticalscience.com/Why_David_Archibald_is_wrong_about_solar_sea_level.html

and http://www.skepticalscience.com/Why_David_Archibald_is_wrong_about_solar_sea_level_1B.html

My February post was 624 words and 6 figures. The Skeptical Science responses to date total 3,446 words and 17 figures. The relationship I found between solar activity and sea level is 0.045 mm per unit of annual sunspot number. The threshold between rising and falling seal level is a sunspot amplitude of 40. Below 40, sea level falls. Above that, it rises.

So let’s apply that relationship to the know sunspot record back to the beginning of the Maunder Minimum and see what it tells us. This is the result:

Figure 1: Back-tested Sea Level from 1645

The figure shows sea level falling through the Maunder Minimum due to the lack of sunspots and then fluctuating in a band about 60 mm wide before increasing rapidly from 1934. It then shows sea level peaking in 2003 before declining 40 mm to 2040.

That is pretty much in agreement with the data from the last 150 years, as per this figure combining coastal tide gauge records to 2001 and the satellite record thereafter:

Figure 2: Sea Level Rise 1850 with a Projection 2040

The glaciers started retreating in 1859, with sea level responding with a rise of 1 mm per annum up to 1930. There was an inflection point in 1930 with the rate of sea level rise almost doubling to 1.9 mm per annum. Sea level also stopped rising from 2003. So the back-tested model and the sea level record are in agreement for at least the last 150 years.

Jevrejeva et al (http://www.psmsl.org/products/reconstructions/2008GL033611.pdf) reconstructed sea level back to 1700:

Figure 3: Global Mean Sea Level Reconstruction since 1700

This longer term reconstruction shows the rise of sea level once the glaciers started retreating. It also shows the acceleration of sea level rise from the early 1930s. As Solanki noted in 2004, the Sun was more active in the second half of the 20th Century than at any time in the previous 8,000 years: http://earthobservatory.nasa.gov/Newsroom/view.php?id=25538 A sea level response to that would be expected.

In summary, the sea level trend fluctuations driven by the internal variability of the ocean-atmosphere coupled system were overprinted by higher solar activity from 1933 to 2003. The period of best fit within that, from 1948 to 1987, has allowed the solar component of sea level rise to be elucidated.

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