Time to break my lengthy science drought by trying to get back up to speed on what sea level is supposed to do. Sea levels rising faster than expected: scientists says Reuters, and they lead with Stefan Rahmstorf predicting more than a meter in 100 years. Reuters make the common mistake by saying The U.N.’s Intergovernmental Panel on Climate Change in 2007 predicted global warming would cause sea levels to rise by between 18 cm and 59 cm (7 inches and 23 inches) this century. To be fair to them, IPCC practically begged people to get this wrong; that is the value excluding weird things happening to ice sheets (Lomborg makes the same mistake, but he knows this stuff too well to do it accidentally: from him, it is deliberate misinformation; SR calls Lomborg on this, but more politely than me). Unfortunately, the chances of weird things happening is still unknown.
One thing that is worth pointing out (an observation not new with me; I think SR may be the first to say it) is that the IPCC low-end 18 cm is utterly implausible. SLR is already 1.8 mm/yr, and it isn’t going to slow down. Quite what the current value is I’m not sure… lets look at IPCC: From 1961 to 2003, the average rate of sea level rise was 1.8 ± 0.5 mm yr-1. For the 20th century, the average rate was 1.7 ± 0.5 mm yr-1, consistent with the TAR estimate of 1 to 2 mm yr- 1. and For the period 1993 to 2003, the rate of sea level rise is estimated from observations with satellite altimetry as 3.1 ± 0.7 mm yr-1, signifi cantly higher than the average rate. The tide gauge record indicates that similar large rates have occurred in previous 10-year periods since 1950. It is unknown whether the higher rate in 1993 to 2003 is due to decadal variability or an increase in the longer-term trend.
Reuters are quoting folk from the recent International Scientific Congress Climate Change in Copenhagen (note that this *wasn’t* an IPCC conference; if you believe the about stuff it was just a U Copenhagen event). So while the conference “key message” is suitably apocalyptic, it isn’t really clear who is signed up to the message; if you believe the disclaimer, no one is. Ho ho, via BL I find that This is not a regular scientific conference. This is a deliberate attempt to influence policy. Ah well.
So what do people actually say in their abstracts? Church, Gregory et al. are sensible people. But saly they followed the traditional pattern of writing their abstract before finishing their talk, so there isn’t much of use there. Sea level has been rising at close to the upper end of the IPCC Third Assessment Report (and AR4) projections. Despite the importance of sea-level rise, the last two IPCC reports have not been able to satisfactorily close the se-level budget [sic]. Here, we present updated estimates of the observed rate of rise from both satellite altimeter and in situ observations. We will build on recent progress in closing the sea-level budget… Two useful things there: first, the boring one: the sea level budget still isn’t closed: or in everyday speech, you can’t get the observed sea level rise out of the known contributions, without some violence to error margins. Second, SLR is *close to* the IPCC upper end: *not* above it.
Grinsted et al. say what they said before. And they are part of a strand of thought which has given up on getting future SLR out of the GCMs, and will get it from historical analogues instead. Bamber et al. reassess the likely SLR from a collapse of W Ant.; this comes into the “scientifically interesting but practically useless” category, because the question at issue is not whether it will be 5m or 3.5m or something else, but how fast it will occur. And the answer to that is still “probably nothing much will happen this century or the next, but who knows”.
Dahl-Jensen says the Greenland was 5K warmer in the Eemian and SL was 5m higher but Greenland didn’t melt (take *that*, Hansen) completely, only contributing 1-2m of SLR.
So, not a lot going on really. Wot about the blogosphere? IoD says “Sea level rise a red herring?. I think his point is that whilst SLR is easy to understand as being bad, there are lots of other things that could be bad too. Which is true. Nurture doesn’t have much to say, though they pick up on Bamber. Errm, did anyone else comment? Sorry if I missed you – please comment.
Meanwhile, I don’t seem to have got very far in discovering what SLR is likely in the future, mostly because I think no-one knows or even has a very good idea. With all the uncertainties in the models, I’m leaning towards the historical analogue approach, which probably points to something in the 0.5m-1.5m range for the next 100 years. But don’t quote me.
Some of my past art: 2008/09/sea_level_rise_pfeffer_et_al.