In the wake of the Fort McMurray fires I’ve seen many stories talk about the climate change factor (which I considered here and here). The BBC ran a story describing how five “Five Pacific islands disappear as sea levels rise.” [Insert gasp here…]
As with the Fort McMurray Fire / climate change thesis, something fascinating happens when you actually read the fine print.
As is customary for media outlets, the headline is sensational and the article itself is somewhat more balanced. Though I emphasize the key word, “somewhat.” The headline very clearly points a finger at rising sea levels, but the article concedes that the cause of the disappearance of the islands is a combination of “rising seas and erosion.” Further into the article (for those who read that far) it adds “shoreline recession was substantially worse in areas exposed to high wave energy, and that extreme events and inappropriate development were also factors contributing to the erosion.”
The abstract to the paper itself seems to place an entirely different emphasis on which were the major factors and which had a smaller contribution.
Sea-level rise has been predicted to cause widespread erosion and inundation of low-lying atolls in the central Pacific. However, the limited research on reef islands in the western Pacific indicates the majority of shoreline changes and inundation to date result from extreme events, seawalls and inappropriate development rather than sea-level rise alone.
The paper seems to want to place the majority of the emphasis on factors other than rising sea levels. In fact, in the discussion section of the paper the authors even threw in another interesting hypothesis,
Relative sea-level rise can also be the result of tectonics, the Solomon Islands are in a particularly tectonically active part of the globe with the convergence of the Pacific Plate, Solomon Arc block and Australian Plate causing localised crustal deformations manifesting as either island subsidence or uplift.
So to the previously listed potential factors we can add the possibility that the islands only appear to have a relatively high sea level rise because they are actually sinking into the earth. The paper does not advance this as an explanation, but points out that this is something worth considering (as stated in the conclusion).
How did we go from a paper that concludes the “majority” of shoreline changes were due to factors other than sea level rising, to a headline that reads, “Five Islands disappear as sea levels rise?” It reaffirms my belief that you should never trust a headline.
And, about that rising sea levels thing. According to the paper,
Rates of sea-level rise in the Solomon Islands over the past two decades are amongst the highest globally, averaging 3 mm / yr since 1950 and 7–10 mm / yr since 1994.
The paper examines these islands during a time span starting in 1947 and ending in 2014. How much did the sea level rise during that time?
1947 -> 1994: 3 mm / year for 47 years
1994 -> 2014: 10 mm / year (we’ll assume the highest rate of change) for 20 years
This gives a total sea level rise of 141 mm prior to 1994, and a total sea level rise of 200 mm after 1994, for 341 mm in total. That’s a total of 13.4 inches. Just over one foot in half a century.
And remember, it could be that the sea level is rising or it could be that the islands are sinking. Or some combination.
Which ought to inspire the astute reader to ask about tides. Surely the tidal changes that occur on a daily basis – and which have absolutely nothing to do with climate change – exceed 13 inches over the course of a single day. Indeed they do. Here’s a link to a page that shows the tidal variations for the capital of the Solomon Islands – Honiara. The web page is dynamic, obviously, but the day I looked at it there was a note at the top that read, “max tidal range 0.98m 3.2ft.”
Over the course of a single day the tides in the Solomon Islands can rise and fall almost three times as much as the average sea level allegedly rose over the past half century. That ought to confirm to us the reality that if sea level rising due to anthropomorphic climate change is a contributing factor – and I’m not ruling that out – it clearly cannot be the main factor, otherwise those islands would have disappeared and reappeared multiple times each week.
It can be very interesting to actually investigate these matters instead of simply reading the article; or worse, only reading the headline!