OK, so maybe I’ll start looking at some of the issues relating to global warming, with three caveats. One is that I have little time to devote to it (I’ll not bore you with a list of my current projects and responsibilities, but obviously we all have limited time and attention, and I really don’t understand the implication, as I see it, that there’s something wrong with my not devoting some of that limited time and attention to “Issue X”). The second is that I’m actually more interested in the way the debate conducted (by both sides) in a manner that is fairly classically described by the science policy literature, so I will continue to look at that as well as discussing the substantive issues. The third is that I’ll address whatever particular element of the issue interests me at any particular moment (I am open to suggestions about which elements to look at). I won’t claim expertise at any particular point; I hope that Michael Heath and Lance will bring their best arguments to bear on the particular element of each post, but keep the focus on that element instead of wandering far afield into “whether it’s happening or not.” I’ll state what I believe to be facts, but if I make a factual error–or you think I do–correct me, with appropriate citations, not claims.
So the first issue I’m touching on is loss/gain of land in Bangladesh, because Lance rebutted my comment about Bangladesh losing land.
Bangladesh is generally expected to lose land because of sea level rise. Global warming can cause sea level rise in two ways: thermal expansion and land-ice melting. Loss of land is a serious threat to Bangladesh because so much of their land is low-lying (being river-formed delta), and because it is one of the world’s most densely populated countries. They’re too poor to simply adapt, and the “escape route” is through India, which has very little interest in allowing potentially millions of Muslim refugees to come on in. Technorati.com reports that a populated island in the Bay of Bengal is disappearing, with the coast is rising between 4 and almost 8 millimeters per year, depending on where one measures it. (That’s a bit confusing–I assume they don’t mean the coastline is actually rising in altitude, but that the sea is encroaching that far inland.
But what if Bangladesh as a whole is not losing land? That’s a pretty significant issue. And apparently Lance is right. I say “apparently” because I can’t find a peer-reviewed article, only a news article. But I don’t (yet) see anyone disputing the factual claim, although the article is two years old. Here is the source from which I take the information.
The claim is that Bangladesh’s landmass has increased by 20 square kilometers annually, with an increase of 1,000 square kilometres since 1973 or so. The sources of the land are the Ganges and Brahamaputra, rivers flowing down from the Himalayas and bringing sediment down to the southern coast (surely some from the mountains–which have plenty to spare–but presumably mostly from below the mountains where the soils are less consolidated). The report agrees that rising ocean levels are taking land from Bangladesh, but that the sedimentation is more than compensating for that. This would mean that rising sea levels are harming Bangladesh, but far less severely–only reducing the rate of landmass growth rather than causing landmass loss. (I’d much rather have someone limit my rate of wealth growth, as opposed to taking wealth from me.)
A scienceblogger disdains the significance of the finding, saying;
Regardless of the extent of the Bangladeshi delta, obviously the only thing that will determine if it is submerged or not in future sea level rise scenarios will be its altitude. 640 square km of new land is great, but if it is all below one metre of sea level rise then it may not last til the end of the century. Approximately 50% of existing Bangladesh would be submerged as a direct result of 1 metre of sea level rise, more would be vulnerable to increased erosion. I dare say that most if not all of the new land being created from silt deposits is both very low altitude and very vulnerable to erosion and will join the unfortunate half destined to be continental shelf sooner or later.
I do know a little about geography, and about simple math, and this is a load of thoughtless BS. Delta silting effects altitude–anyone who doesn’t think so needs to explain how land can accumulate without increasing altitude, and might want to explain to me how the bed of the Mississippi River came to be twenty feet above sea level.* What determines whether Bangladesh (ahem, some of it, not all of it as he careless suggests) is underwater is a combination of a) delta-building, b) delta subsidence (being made of unconsolidated soils, deltas compress over time), and c) sea-level rise. If a) outstrips b) and c), then you’ll get land-gain, not land-loss. As to vulnerability to increased erosion, yes the most seaward extents of the delta are most vulnerable to erosion, but the extension of the delta’s seaward extent protects the prior, more landward, depositions of sediment. That should be obvious to anyone who’s paid any attention to Louisiana’s loss of delta–i.e., anyone who kept half an eye on the effects of Hurricane Katrina.
Finally, this scienceblogger didn’t read the whole article, which notes that ”
Dams built along the country’s southern coast in the 1950s and 1960s had helped reclaim a lot of land and he believed with the use of new technology, Bangladesh could speed up the accretion process, he said…Bangladesh, a country of 140 million people, has built a series of dykes to prevent flooding.
“If we build more dams using superior technology, we may be able to reclaim 4,000 to 5,000 square kilometres in the near future,” Rahman said.
I’ve never before heard that Bangladesh had built dams and dykes to help hold onto sediment and prevent flooding. There’s another very low lying country–in fact one that is already lower lying than Bangladesh, with much of it being below sea level–that has also used dykes to reclaim land: the Netherlands. It’s possible. It’s costly, of course, and rising sea levels will increase that cost (although I have no idea by how much). But they’re already doing it–they’ve already determined it’s a net benefit.
So does Bangladesh’s apparent landmass increase either disprove global warming or mean it doesn’t have significant impacts? The first claim would be wildly irresponsible, and the second would be marginally less so. But two important conclusions do come from it. One is that the strong predictions of catastrophe for Bangladesh are, at the least, far less certain than claimed. The second is that the error comes from a failure to incorporate all the relevant facts into the analysis. That’s a charge frequently directed at AGW adherents, and one that seems to me to be more often dismissed somewhat angrily than satisfactorily rebutted.
A comment on the linked article’s reference to James Hansen, whom I have critiqued and Michael Heath has defended. The article reads,
The [IPCC] has predicted that impoverished Bangladesh…will lose 17 per cent of its land by 2050 because of rising sea levels due to global warming.
…Director of the US-based NASA Goddard Institute for Space Studies, professor James Hansen, paints an even grimmer picture, predicting the entire country could be under water by the end of the century.
Well, given that Bangladesh has a number of mountains near to or over 1,000 meters, this seems to be an amazing claim. But it’s not certain that Hansen ever said any such thing. The article does not quote a source. The source appears to be a British newspaper article, which has the following:
I turned to Professor James Hansen… He believes the melting of the Greenland ice cap …suggests we are facing a 25-metre rise in sea levels this century – which would drown Bangladesh entirely.
So it’s not Hansen who’s claiming Bangladesh would be wholly drowned, but a British reporter who misunderestimates the heights of Bangladesh’s northern portions. Does Hansen suggest a 25 meter rise in sea level? Well, sort of, and there he does note that “practically the entire nation of Bangladesh” lives within 25 meters of sea level. That’s probably true, since the Himalayas are far more sparsely populated than the deltas. So Hansen does suggest a threat to the nation (i.e., the populace), which the reporter carelessly transmutes into an inundation of the country.
*According to John McPhee in Control of Nature, and my geologist friend who is from Louisiana.