Scientists forecast metre rise in sea levels this century says The Grauniad. I strongly suspect they have garbled things, though I admit I haven’t read the original Science paper. I have read the NCAAR/UCAR press release Arctic, Antarctic Melting May Raise Sea Levels Faster than Expected.
The Grauniad continues Half of Greenland and vast areas of Antarctica are destined to melt if global warming continues at the same pace until the end of the century, scientists warned yesterday. Their research shows that the loss of so much ice will trigger dramatic rises in sea levels, ultimately swamping low-lying regions of Essex, Lincolnshire and Norfolk and threatening the flood defences of cities such as London, Liverpool and Bristol. The last time so much ice was lost from the poles – in a period between ice ages 129,000 years ago – global sea levels rose by four to six metres.
Now, as far as I can see, this is – deliberately or accidentally – mixing up two things. If you read this quickly, you expect half of greenland to melt *within the century*. But thats *not* what it is saying. It is saying (and this is clearer, but still not very clear to the casual reader) from the NCAR press release that by 2100 temperatures will be as high as they were during the last glacial, and that given enough time this would be expected to melt the ice sheets to the degree that they melted then. What it *doesn’t* mention is that this is likely to take a thousand years or more (dependent on the exact degree of T rise, of course).
However, that simply comes into the “heard it all before” category – what exactly is new about this?
Working from the press release, the modelling component says that GW could wam the arctic by 3-5Â°C by 2100, and that this is roughly as warm as it was 130,000 years ago in the last interglacial (maybe, maybe, I’d have said the last interglacial was perhaps a shade cooler than that, but am not sure. No matter, continue…). Then The CCSM suggests that during the interglacial period, meltwater from Greenland and other Arctic sources raised sea level by as much as 11 feet (3.5 meters), says Otto-Bliesner. However, coral records indicate that the sea level actually rose 13 to 20 feet (4-6 meters) or more. Overpeck concludes that Antarctic melting must have produced the remainder of the sea-level rise. OK, so this is starting to make sense: where exactly previous sea level rise came from (arctic, antarctic, whatever) is a research topic. It looks like these people were maybe working on partitioning this rise between the different ice sheets (which fits the abstract Simulating Arctic Climate Warmth and Icefield Retreat in the Last Interglaciation). So, the CCSm people have got round to coupling their AOGCM to an ice sheet, only a few years after the Hadley Centre did the same. They’re doing well to get this into Science, though! Then there is the palaeo paper, Paleoclimatic Evidence for Future Ice-Sheet Instability and Rapid Sea-Level Rise, which has an abstract that looks positively designed to sow the confusion that the papers have fallen into, Polar warming by the year 2100 may reach levels similar to those of 130,000 to 127,000 years ago that were associated with sea levels several meters above modern levels; both the Greenland Ice Sheet and portions of the Antarctic Ice Sheet may be vulnerable.
So this is (once again) the idea that once CO2 levels get high enough, we will be committed to melting Greenland. Which is fair enough, but it *isn’t news*. Is it something to worry about? That depends on a lot… suppose we assume this melt happens linearly over 1kyr; thats 5m/1kyr = 5mm/yr, or 0.5m/century. And you can add on thermal expansion and maybe some Antarctic melt and other stuff on to that. But still, 0.5m/century is not *fast*. It is, though, cumulative. How will our descendants cope with 5+m of SLR? I would guess that this would cause large problems over many parts of the world, if we were at todays tech levels. But we won’t be: we’ll be back in the stone age by then… or we’ll have reached the nearer stars… who knows, really?