Thursday, February 11, 2010

Sea Level Rise - Part 1

I have begun to take a closer look at available sea level data. Frankly, I'm a bit surprised. Of course I've heard of sea level rise (SLR) before, but it was like a fuzzy abstraction. I didn't have specific figures to ponder.

In this particular post I will only discuss paleoclimate data. There's some data that I imagine is pretty well known. The figure to your right, for example, comes from Wikipedia. It's a sea level reconstruction from Fleming et al. (1998) of the last 20 thousand years or so. That's roughly the time span since the last glacial maximum (LGM), when the global mean temperature was 5°C lower than today, give or take. As the LGM ended, and the planet entered the current interglacial period, sea level rose by about 130 meters (427 feet.) Of course, much of that is probably the result of ice melt, and there was a lot of ice in the LGM.

Then there's data that is not well known as far as I can tell. For example, there's a 380,000-year reconstruction contributed by Siddall et al. (2003) based on oxygen isotope records from Red Sea sediment cores. The following graph shows this sea level reconstruction along with the Vostok station temperature reconstruction provided by Petit et al. (2000).

If there were any doubts that temperature drives sea level, I believe the graph above is enough to dispel them. This is the basic premise I wanted to establish with this first post.

The data has some features that I wish to explore further, but not today. In particular, notice that sea level lags temperature by several thousand years. (This is not so clear with sea level data older than about 250,000 years. I'm guessing there's some sort of dating error either in the Red Sea data or in the Vostok data once you go that deep.) If I only consider data for the last 50,000 years, I'm estimating that the best lag is about 4,700 years. I'm not sure I can emphasize enough how important this lag is, but I'll certainly try.

[In Part 2 I estimate SLR due to ice melt alone since the LGM.]


drj11 said...

Do you have a link to the Fleming data? If it's available it would be a good addition to the CKAN climate data group.

Joseph said...

@drj11: No. I asked in Wikipedia where I could find it, but I didn't get an answer.

That's a good resource, BTW.