New Zealand?s ocean temperature increase over the 20th century is consistent with the global average upward trend. Sea level along the country?s shoreline has been rising accordingly by an average of 0.04-0.08 inches (1-2 mm) per year
2 mm per year = 2 cm per decade = 20 cm per century = 8 inches.
Hardly a disaster and a continuation of present trends, which have seen the sea levels rise about a foot since 1850. Sea levels have risen about 300 feet since the end of the last Ice Age, yet somehow humanity adapted.
I do not understand how the seas supposedly can rise less than 1 mm per year around in Tuvalu, but over 20 mm per year in Micronesia, less than 2000 mi away in the same ocean? I notice that the Micronesia number came from a newspaper article, not a scientific paper.
A second problem with the above range is that the models used to derive this projection significantly underestimate past sea level rise. We tried in vain to get this mentioned in the SPM, so you have to go to the main report to find this information. The AR4 states that for the period 1961-2003, the models on average give a rise of 1.2 mm/year, while the data show 1.8 mm/year, i.e. a 50% faster rise. This is despite using observed ice sheet mass loss (0.19 mm/year) in the “modelled” number in this comparison, otherwise the discrepancy would be even larger – the ice sheet models predict that the ice sheets gain mass due to global warming. The comparison looks somewhat better for the period 1993-2003, where the “models” give a rise of 2.6 mm/year while the data give 3.1 mm/year. But again the “models” estimate includes an observed ice sheet mass loss term of 0.41 mm/year whereas ice sheet models give a mass gain of 0.1 mm/year for this period; considering this, observed rise is again 50% faster than the best model estimate for this period. This underestimation carries over from the TAR models (see Rahmstorf et al. 2007 and the Figure below) – this is not surprising, since the new models give essentially the same results as the old models, as discussed above.
Comparison of the 2001 IPCC sea-level scenarios (starting in 1990) and observed data: the Church and White (2006) data based primarily on tide gauges (annual, red) and the satellite altimeter data (updated from Cazenave and Nerem 2004, 3-month data spacing, blue, up to mid-2006) are shown with their trend lines. Note that the observed sea level rise tends to follow the uppermost dashed line of the IPCC scenarios, namely the one "including land ice uncertainty", see first Figure.
We therefore see that sea level appears to be rising about 50% faster than models suggest – consistently for the 1961-2003 and the 1993-2003 periods, and for the TAR models and the AR4 models. This could have a number of different reasons, and the discrepancy could be considered not significant given the error ranges of observations and models. It is no proof that models underestimate future sea level rise. But it is at least a plausible possibility that the models may underestimate future rise.
Interesting that the models under-predict sea-level rise, when they are assuming ice cap mass loss, while the ice cap models predict ice cap mass increase due to to global warming, which would slow sea level rise. Enough ice cap mass increase, and it could offset thermal expansion entirely.
Sounds like the models still need work. Perhaps because your background is not in engineering, you find numbers convincing when they come out of a model. But obviously, each model only models a small piece of the climate, which we don't know how to model in its entirety, and models only show what they are designed to show - that is, if you are lucky and have top-flight programmers.
BTW, even the top observed number of 3.1 mm/year = about 1 foot per century.
This is a calamity? |
