Friday, 22 February 2013

Climate Central scores grade F in geography

There's a lot of it about - sea I mean. There's also a lot of reports around just now in which alarmists appear almost to be gloating over a paper in Geophysical Research Letters titled The gravitationally consistent sea-level fingerprint of future terrestrial ice loss (Spada et al . 2013), [h/t Spiel Climate.] That bastion of truth and objectivity might not be said to be gloating, but there's an element of "See - told you so!" in their article Ice Melt Means Uneven Sea Level Rise Around the World. More of that and their "grade F" later.

What that paper says (in essence) comes as no surprise to me. Sea level rise around the globe is far from even. There are many reasons for that "lumpiness", two of them being thermal expansion and gravitational effects.
We solve the sea-level equation to investigate the pattern of the gravitationally self-consistent sea-level variations (fingerprints) corresponding to modeled scenarios of future terrestrial ice melt. These were obtained from separate ice dynamics and surface mass balance models for the Greenland and Antarctic ice sheets and by a regionalized mass balance model for glaciers and ice caps. For our mid-range scenario, the ice melt component of total sea-level change attains its largest amplitude in the equatorial oceans, where we predict a cumulative sea-level rise of ~25 cm and rates of change close to 3 mm/yr from ice melt alone by 2100. According to our modeling, in low-elevation densely populated coastal zones, the gravitationally consistent sea-level variations due to continental ice loss will range between 50 and 150% of the global mean. This includes the effects of glacial-isostatic adjustment, which mostly contributes across the lateral forebulge regions in North America. While the mid range ocean-averaged elastic-gravitational sea-level variations compare with those associated with thermal expansion and ocean circulation, their combination shows a complex regional pattern, where the former component dominates in the Equatorial Pacific Ocean and the latter in the Arctic Ocean.
That mouthful is down to modelling, of course, and if you accept their estimates of ice melt, I see little wrong with their results. What I do see that's wrong, is all the alarmist pundits jumping on the bandwagon and extrapolating what the paper says about their little corner of the globe, or the "poster-children" of predicted sea-level rise, like Bangladesh, Tuvalu, etc. As my pet subject is the study of sea-level and changes thereof, I find myself often peering at maps while I sip my gin-and-tonic. Authors of articles like the one at Climate Central might find it beneficial to do the same - peering, that is, though sipping G&T would do them no harm either. Alex Kirby, their geographer in chief, says
Improved projections of the contribution of ice to sea level rise produced by Ice2sea will feed into the fifth assessment report of the Intergovernmental Panel on Climate Change. In 2007, the IPCC’s fourth report highlighted ice-sheets as the most significant remaining uncertainty in projections of sea-level rise.
The researchers found that ice melt from glaciers and from the Greenland and Antarctic ice sheets is likely to be critically important to regional sea-level change in the equatorial Pacific ocean
There the rise will be greater than the global average increase, affecting in particular western Australia, Oceania and the small atolls and islands in the region, including Hawaii. Another area which should expect an above-average increase is the east coast of South Africa and Madagascar.
The first paragraph is interesting - "will feed into the fifth assessment report of the Intergovernmental Panel on Climate Change" given that it's just undergone the review stage. Late entries anyone? However, the next paragraph states exactly what's in the abstract above; "regional sea-level change in the equatorial Pacific ocean", yet what Alex considers to be in the equatorial Pacific ocean is interesting. He thinks western Australia and Hawaii are included, and he also appears to think that the Hawaiian islands are "small islands".

Given that Honolulu is only a couple of degrees south of the Tropic of Cancer, and that only half of the western Australian coast is north of the Tropic of Capricorn, I think he's stretching the definition of "equatorial" just the teeniest bit. The biggest of the Hawaiian islands is about 250km north-south.  Still, why let a few inconvenient geographical facts stand in the way of a good story?

Perhaps he, other alarmists, and IPCC authors, might like to peruse the abstract of A synthesis of the Antarctic surface mass balance during the last 800 yrs (Frezzotti et al 2013) [h/t Greenie Watch]
Global climate models suggest that Antarctic snowfall should increase in a warming climate and mitigate rises in the sea level. Several processes affect surface mass balance (SMB), introducing large uncertainties in past, present and future ice sheet mass balance. To provide an extended perspective on the past SMB of Antarctica, we used 67 firn/ice core records to reconstruct the temporal variability in the SMB over the past 800 yr and, in greater detail, over the last 200 yr.
Our SMB reconstructions indicate that the SMB changes over most of Antarctica are statistically negligible and that the current SMB is not exceptionally high compared to the last 800 yr. High-accumulation periods have occurred in the past, specifically during the 1370s and 1610s. However, a clear increase in accumulation of more than 10% has occurred in high SMB coastal regions and over the highest part of the East Antarctic ice divide since the 1960s. To explain the differences in behaviour between the coastal/ice divide sites and the rest of Antarctica, we suggest that a higher frequency of blocking anticyclones increases the precipitation at coastal sites, leading to the advection of moist air in the highest areas, whereas blowing snow and/or erosion have significant negative impacts on the SMB at windy sites. Eight hundred years of stacked records of the SMB mimic the total solar irradiance during the 13th and 18th centuries. The link between those two variables is probably indirect and linked to a teleconnection in atmospheric circulation that forces complex feedback between the tropical Pacific and Antarctica via the generation and propagation of a large-scale atmospheric wave train.
Perhaps Spada et al should have waited a bit before publishing. Perhaps Alex should read more - an atlas maybe? Perhaps I'll have another G&T.

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