Yes, we know that “the climate has always changed”…

… but that’s not the point. Here’s what that point really is.

The concentration of global, atmospheric CO2 today exceeds 400 ppm. The last time that happened on Earth was something like 2–5 million years ago, in the Pliocene Epoch (the one that came just before the Pleistocene). At that time, global average temperature was 2–3ºC higher than today. Back then, humans (this was the transition from the genus Australopithecus to the genus Homo) were doing stuff like this:

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What’s more, and this part is key, sea levels were higher than they are today. It’s a bit of a sticky wicket to determine how much higher – and this is an important component of ongoing climate research – but the range of estimates cover about 5–40(!)m higher. Yes, the prospect of a 40-m rise in sea level should terrify you, and even a 5m rise could still be devastating. Let’s take a moderate value for the sake of argument and run with a 20-m rise under a scenario of 2–3ºC warming under CO2 concentrations above 400 ppm. (Limiting global temperature by 2100 to even 3ºC above the current baseline is looking increasingly optimistic, unfortunately. International plans are calling for action to keep us from an increase of 1.5ºC by 2100, and there is little chance of that happening.) Of all the things that happen when sea levels rise, our focus needn’t be anywhere other than on the most obvious problem: there is less land.

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There’s a good chance that babies born today will experience a world 80 years hence that is an astounding 4ºC warmer than it is today.

Of all the things that happen when sea levels rise, our focus needn’t be anywhere other than on the most obvious problem: there is less land.


Rather unlike our nomadic hunting ancestors of the Pliocene, today’s humans number more than 7.7 billion. Each one of us is a mouth to feed, at the very least. Even more troubling, however, is where we are: Nearly 50% of us live within about 200km of a coastline. That’s 3 billion people. By 2025, that number is estimated to be 6 billion. There’s also a heck of a lot of our food still grown on our broad coastal plains, and we are going to need as much productive farmland as we can muster as our population continues to edge upward toward about 9 billion. Land use change – generally from farmland, forest, and wetland to suburban and urban land uses – is occurring twice as fast in coastal zones of the Lower 48 US states than elsewhere in the country.

So we have constraints in response to a warmer climate today that Homo habilis did not. It does not matter that global climate changes over time or that alligators once bellowed from swamps in the primordial Alaska. What matters is the effect of such changes on the people and the infrastructure that must find a way to adapt to those changes. As coastal zones face increasing pressure from rising sea level, billions of people will be displaced over the next century. Think of a war that was not on some level about land. I’ll wait. (I assume some military historians might be able to argue for at least a couple of examples but in general it’s no contest: wars are fought over access to natural resources, i.e., land.)


Think of a war that was not on some level about land.


Quips about my future oceanfront property in Oklahoma aside, rising sea levels will mean less land for people, less land for growing food to feed people, refugee crises, famine, disease, and war.

That’s the point.


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