This will hopefully be the first in a fairly long series of posts on what a future of “heroic survival” on a hot and hostile world might look like, in the event that our best efforts are not enough to stave off severe and permanent global warming. I'll start with a list of possible coping strategies, in roughly descending order of cost, to the most sensational predicted effect: the drowning of the world's coastlines and some entire low-lying island nations.
1. Denial. Yes, if you're lucky, it will turn out that the current long-term trends are meaningless and the ice caps will stop melting within a few years. But if you're wrong, the cost of doing nothing is quite simply the loss of the land where 2.75 billion people will live by 2025. The economic impact of such a calamity is scarcely imaginable, even presuming there is actually a global economy still standing afterward to reckon the damage.
3. Geo-engineering. The proposal sounds absurd, but I've now heard a couple versions of the idea of pumping the excess water from the oceans inland to form new saltwater seas (one was in Kim Stanley Robinson's novel Sixty Days and Counting, but I'm pretty sure the other was intended seriously). Quite apart from the possible side effects of such vast modifications to Earth's surface, I can't imagine where they imagine we'd get the energy to pump that much water. Back-of-the-envelope calculations say we'd have to move between three and four hundred trillion tons of water to counteract a one-meter sea-level rise, and if either Greenland or the West Antarctic Ice Sheet collapses, the projected rise is six meters.
4. Planned migration. As previously noted, a huge and growing fraction of the human population lives in coastal cities and towns. If we're lucky and the seas rise gradually rather than in sudden jumps, these settlements could move inland like amoebas, building new structures on their landward side to replace those abandoned to the inexorable tide. But with their construction industries swamped by the equally inexorable flood of migration from rural to urban areas, how will cities find enough excess construction capacity to execute such a plan? It won't be cheap, and neither will the cost of replacing the produce of the absorbed farmland. (Green roofs are awesome, but they can only do so much.)
5. Holding back the tide. This is another concept from Robinson's Science in the Capital trilogy, where he describes a fictional island ringed by a huge earthen wall, inside which the land is all below sea level. But Lois McMaster Bujold describes a more globally typical case in her far-future novel Brothers in Arms, part of which takes place inside a huge barrier across the mouth of the river Thames. Most coastal cities and towns are like London in that, if you simply built a wall along the coastline, water from one or more rivers would build up against it until it overflowed. Bujold's solution is a system of giant pumps that bring incoming river water up to the new sea level. A more practical, if ironic, solution might be to deliberately overexploit your water resource, piping as much of it away to farms and other cities as possible, so that the nearby rivers simply never reach the sea.
6. Raising the land. If we can build artificial islands and peninsulas, why not truck in even more immense quantities of dirt and rock to raise the street levels of low-lying coastal cities by several meters? (In the case of places like Tuvalu, where there is no higher ground to dig into, the dirt would have to be shipped in.) Earth-moving costs might be reduced somewhat if the lower above-ground stories of taller buildings are turned into basements rather than simply crammed full of dirt. Some of the many one- and two-story buildings could perhaps be raised to the new ground level rather than merely buried, while others might be reinforced and provided with light pipes to make underground living moderately bearable.
7. Welcoming the sea. Imagine a typical coastal city with street levels about a meter above the existing high tide-line. Now imagine that, as Greenland melts away, the lower two stories (roughly six meters) of every tall building are wrapped with thick new outer walls made of reinforced eco-friendly concrete, manufactured using a technique that mimics the growth of coral. As with the previous solution, you get two new basement levels for each building; meanwhile, the tops of the walls become the new sidewalks. Throw in some railings and a bunch of pedestrian bridges, populate the newly flooded streets with electric and paddle- and pedal-driven boats of every description, and voila: a new Venice, for a fraction the cost of rebuilding the whole place on higher ground. Short structures would again be a challenge; some could be raised on stilts or equipped with pontoons, but extensive programs to cram more residents into skyscrapers would probably be necessary. Meanwhile, a few rich eccentrics might water-harden their roofs and walls so they could live in inverted aquariums, perhaps with intentionally convoluted nooks and crannies in the outer walls to provide habitat for the many fish who will have been rendered homeless by the death of nearly every bit of real coral on the planet.