Sea rise not that scary?

That's the case that climate adaptationist Bjorn Lomborg (don't call him a skeptic) makes at Project Syndicate, because we've dealt with it already:

Imagine that over the next 70 or 80 years, a giant port city – say, Tokyo – found itself engulfed by sea levels rising as much as 15 feet or more... Without a vast, highly coordinated global effort, how could we possibly cope with sea-level rises on that order of magnitude?

Well, we already have. In fact, we’re doing it right now. Since 1930, excessive groundwater withdrawal has caused Tokyo to subside by as much as 15 feet, with some of the lowest parts of the downtown area dropping almost a foot per year in some years. Similar subsidence has occurred over the past century in a wide range of cities, including Tianjin, Shanghai, Osaka, Bangkok, and Jakarta. In each case, the city has managed to protect itself from such large sea-level rises and thrive.

Lomborg cites research research claiming that over 95% of the world's coastal population is urban, making rising oceans no big deal.

A 20-foot rise in sea levels (which, not incidentally, is about ten times more than the United Nations climate panel’s worst-case expectations) would inundate about 16,000 square miles of coastline, where more than 400 million people currently live... [and] the vast majority of those 400 million people reside within cities, where they could be protected relatively easily, as in Tokyo.

Off the top of my head, I'd challenge this with Bangladesh, which has 160 million people and is very low-lying:

Is it really fair to assume Dhaka has an easy out just because it's "urban"? Maybe Jakarta has coped with rising seas, but Indonesia's per capita GDP is still 3x that of Bangladesh.

Lagos and Karachi are two other poor coastal megacities that would be worth doing the same analysis for.

Update: I just had dinner with someone from Bangladesh who confirmed that the idea that rising seas won't hit Bangladesh hard is preposterous. First, there are millions of people living in low-lying, non-urban areas (especially hundreds of islands in the Ganges Delta). Second, much of the productive agricultural land is similarly low and is already suffering from soaring salinity in many areas. So it seems that the underlying analysis is weak, and Lomborg himself should be doing better quality control of the sources he chooses to cite.

Update 2: A few relevant numbers to refine our back-of-the-envelope: 46% of Bangladeshis live within 10 meters of the average sea level, and the country is only 27% urban. So it seems very unlikely that Lomborg's math that "only ~15 million people would need to be relocated [over the course of the century]" can possibly be right.