As we look at what preparations need to be made for rising sea levels, it’s worth taking a moment to think about the pattern of sea level rise. Over the 20th century, it progressed at a fairly steady rate, and most of the rise was due to thermal expansion of water. The oceans absorbed a huge amount of the heat trapped by the greenhouse gas increase, and that’s what led to the few inches sea level we saw by the year 2000.

The 21st century is different. We’re now facing sea level rise due to melting ice on Greenland and Antarctica, and so the pattern of rise is likely to change. Of particular concern are the glaciers and ice shelves that are currently resting on the sea floor, held in place by the topography of the land underneath them.

As the warming waters get up under the ice sheets, there’s no clear prediction for when they’ll eat away enough ice to let the ice float free. When that happens, we could see a dramatic increase sea level – a foot or more per decade.

When we hit that point – and it is a matter of when, not if – the time for preparation will be over, and we’ll be mostly locked into reaction mode. It will mean refugees from coastal cities around the globe, including the U.S.. It will mean big increases in damage from storm surges, and high costs from smaller and smaller storms. If we haven’t planned ahead, we’ll also probably pour billions of dollars down the drain in a sort of automated “we will rebuild” response, and as a result we’ll have fewer resources to deal with the next time it happens, a year or two down the road.

And if it happens while people like the current GOP are in control of the country, it’s not hard to imagine these future calamities making 2005’s Hurricane Katrina look positively tame by comparison.

Even for those who continue to pretend that this is not being caused by human activity, the refusal to even think about preparation is criminal. When ice released from its grounding lines, we won’t have much time to respond before the first disaster hits, especially given the number of people, amount of invested capital, and amount of infrastructure in the danger zone. Who we have in office over the next thirty years is going to matter a lot, and it could mean the difference between a functional nation, and collapse.

For more information and videos on this, check out the “weekend wonk” on climatecrocks.com