Global warming and ocean levels

news @ nature.com-Warnings rise over rising seas-Fresh predictions about climate change prompt news@nature.com to ask what we know about the future of our oceans.

As I have previously posted on the current relatively slow rate of sea level rises, it's only fair that I post about this new study indicating that (on worst estimates) the sea level rise could indeed be very dramatic within a hundred years.

These new estimates are so high above those previously indicated by the IPCC that I expect there may be some legitimate criticism of the studies to come soon. I also have doubts that it matches entirely with other possibilities recently mooted.

Meanwhile, I have been meaning to get some good maps to see where the beach may be in 100 years time, and consider buying land there.

UPDATE: Real Climate's take on the story is very important as a counterpoint to the way this story has been reported in the media. (For those who don't know, Real Climate is in no way a global warming sceptic site. Quite the opposite.)

What does all this news mean in practice? Reading the editorials in Science, and quotations from various researchers in newspaper articles, one might be under the impression that we should now expect "catastrophic sea-level rise" (as Science's Richard Kerr writes). Of course, what is catastrophic to the eye of a geologist may be an event taking thousands of years. In the Otto-Bliesner et al. simulations, it takes 2000-3000 years for Greenland to melt back to its LIG minimum size. And while we don't advocate sticking with the typical politician's time frame of 4 or 5 years, the new results do not require us to revise projections of sea level rise over the next century or so. This is because even with Arctic temperature continuing to rise rapidly, there will still be significant delay before the process of ice sheet melting and thinning is complete. There is uncertainty in this delay time, but this is already taken into account in IPCC uncertainty estimates. It is also important to remember that the data showing accelerating mass loss in Antarctica and rapid glacier flow in Greenland only reflect a very few years of measurements -- the GRACE satellite has only been in operation since 2002, so it provides only a snapshot of Antarctic mass changes. We don't really know whether these observations reflect the long term trend.

So, no need for me to retract my previous posts about there being no need (for the next few decades at least) to talk about Tuvalu sinking beneath the seas. You would never guess that from the general media, but I think Science magazine itself is rather to blame in this case.