Tuesday, 21 February 2012

San Diego - time to get worried?

The powers-that-be in San Diego, California are getting worried about sea-level rise.
Buildings, shoreline parks and recreational facilities, transportation systems, and energy and water facilities are at risk, regional groups said Thursday.
So says U-T San Diego "Plan for sea-level rise in San Diego Bay". The article begins
A coalition of local agencies on Thursday announced one of the nation’s first regional plans to prepare for sea-level rise. Focused on San Diego Bay, it’s designed to help the region adapt to one of the more visible aspects of climate change.
Sea level could rise by as much as 17 inches by 2050 and five feet by 2100, when many areas around the bay could be permanently inundated, according to a recent assessment. The greatest cause for concern is the likelihood of increased frequency and severity of flooding during storms or very high tides.
I notice the neither the current nor past rates of sea-level rise at San Diego are mentioned. The  "coalition of local agencies"  doesn't seem to think it matters,  in common with most such organisations worldwide. It's not clear where the "17 inches to 5 feet" comes from, it's not mentioned in any of the sources I've read. However, Google gives a source for that phrase on Wired, and that article links to Think Progress - where else? Our Joe says 
 Arctic Assessment bombshell: “Global sea level is projected to rise by 0.9“1.6 meter by 2100″. I don't know why there's a strange character (in the title, not our Joe) between the 9 and 1, should be a dash I assume. Anyway, the 5 feet would seem to be a global estimate, so here as elsewhere, planners assume a global prediction rather than get a local estimate.
The analysis was supported by Port of San Diego, San Diego County Airport Authority, The San Diego Foundation and ICLEI–Local Governments for Sustainability USA. Chula Vista, Coronado, Imperial Beach, National City and San Diego also helped develop the strategy.
So that's alright then - these august bodies can surely be trusted to use taxpayers' money in a timely and efficient manner to protect beaches and seafront dwellings, businesses and roads. Romm cites the Arctic Monitoring and Assessment Programme's "Snow, Water, Ice and Permaforst in the Arctic" report. That's not my typo - it's copied from their website. Anyways, it's a global figure, as I said, and quite likely may over- or understate the situation for San Diego. So what is the situation for San Diego? The local tide gauge tells all, from 1906 too.

San Diego Sea-level from 1906-2010  Data Source: PMSL
 No spectacular acceleration evident there, in fact it looks like it's levelling off:

San Diego Sea-level from 1990-2010  Data Source: PMSL
 That seems pretty level to me, but of course I'm not Peter Gleick. He can see the horizon sloping upward from left to right. Those spiky graphs are hard to digest, so let's see if the annual average removes the noise.

San Diego Sea-level - annual average 1906-2010
 That's interesting, if my Mark One Eyeball doesn't deceive me, the 11-year moving average has levelled off after about 1987. One sure way of finding out is to plot the calculated trend over a period of years, for example from 1906-1970, then 1906-1971 and so on.. It's called asymptotic analysis, where the plot might move up and down, but settles at near the true rate as the finish year approaches the end year (here, 2010).

San Diego - evolution annual sea-level trends
 Now that's interesting too -the sharp rise from 1982 is a result of the sharp upward El Niño spike seen in the first chart. There were two large spikes in the El Niño years of 1992-3 and 1997, and these show in the rate change above. However, the rate declined after 1998, and still seems to be dropping. It's lower than it has been since 1983, the second year of the largest spike in the first chart. Bear in mind that a decreasing rate doesn't necessarily indicate declining sea-level, the overall rate is still positive to the end of the trend chart. But the rate is still decreasing, and we've seen that there's been no net rise since 1990.

Gazing into the future is pointless unless your feet are firmly anchored in the present. No bank would advance money solely on the basis of future projections of income. They want to see your current financial situation, and past figures too, in order to assess the validity of those projections and therefore the risk. Is the "coalition of local agencies" listed above even aware of the current "plateau" at San Diego? If not, why not?

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