The oceans are coming, part 3: Remaining afloat
By Keith Farnish and Dmitry Orlov
…In Part I of this series, just a couple of months ago, we cheerfully wrote: “The East Antarctic Ice Sheet (that’s the big blob that surrounds the South Pole just off-centre) seems to be quite stable, and should remain that way for the next few centuries.” That would have been nice, because the East Antarctic ice sheet holds somewhere around 80% of all the fresh water on the planet; if it were to melt, the sea level would go up by between 20 and 36 metres (75 to 120 feet) and coastal maps would need to be redrawn more or less from scratch. But then shortly after we posted the second part of this series, Nature Geoscience published a study showing that the East Antarctic Ice Sheet was undergoing a decline in thickness: In agreement with an independent earlier assessment, we estimate a total loss of 190±77 Gt/year, with 132±26 Gt/year coming from West Antarctica. However, in contrast with previous GRACE estimates, our data suggest that East Antarctica is losing mass, mostly in coastal regions, at a rate of 57±52 Gt/year, apparently caused by increased ice loss since the year 2006. “Accurate quantification of Antarctic ice-sheet mass balance and its contribution to global sea-level rise remains challenging”, the authors are quick to caution. Nevertheless, the study concludes that “in contrast to previous estimates… [the new measurements] indicate that as a whole, Antarctica may soon be contributing significantly more to global sea-level rise”. In Part I we cited the aforementioned GRACE satellite system as a way of assessing potential ice losses from Greenland, and based on it we assumed — wrongly as it turned out — that East Antarctica would be safe. Taking into account everything that has been discussed earlier in this series, this shouldn’t come as a surprise. Typically, we don’t know what exactly to expect or when to expect it, but we do know that it will be worse than what we should have been expecting before. Should we wait to act until scientific certainty has been achieved? If we do, will it be too late to prepare or to adapt? Newsflash! It now appears that a couple of big Antarctic glaciers — Pine Island Glacier and Thwaite’s Glacier next to it — have passed their tipping points. They have floated off the sea-bed, and will now disintegrate, resulting in as much as a half-metre rise above previously estimated sea level by the end of the century. We are not in a position to face down the ocean, saying “This far, Ocean, and not a centimetre further!” Our worst-case scenario is that our worst-case scenario is going to continue getting worse and worse. We cannot limit our planning activities to this or that mythical upper bound. When our knowledge fails us, our myths are there to guide us. The success of Noah’s mission did not depend on having an accurate estimate of how high the waters would rise, because his arc floated. …
