The Mediterranean . . . it’s got these couple of problems. It’s a respectable-sized sea, y’know; it covers an area of 970,000 square miles (2.5 million square kilometers). That much surface area, you get a lot of evaporation. Now, that’d be ok, I mean, some of it rains back in, some comes back in rivers, but the thing is . . . it doesn’t rain all that much . . . relatively speaking. And the rivers that feed into it, they’re a bit on the wimpy side . . . relatively speaking. All appreciation to the Nile for its awesomely important history and everything, but it ain’t no Amazon.
So that’s problem number one. Problem number two: the Earth is molten inside. More specifically, what we call the Earth’s crust—land and ocean bottom—is mostly a thin skin of solid rock floating on melted rock that’s ever-so-slowly churning this way or that, taking big floating hunks of crust with it wherever it happens to be going. Hunks like Africa. Africa’s been floating north-easterly for a while now; a few million years, in fact. So, not very fast, but fast enough to become a problem. Because, y’know how that Straight of Gibraltar is kind of narrow? All it’d take would be for Morocco to hook up with Spain, close the straight, and guess what? Way more water evaporating into the sky than comes back in through rivers and rain. Let that go on long enough, whadda you think’s gonna happen? Thing is, it actually has. More. Than. Once.
The whole period is called the Messinian Salinity Crisis, after the Messinian Age of Earth’s geologic history, during which it occurred. The Mediterranean repeatedly became cut off from the Atlantic Ocean, dried out partially or almost completely, and refilled again when the Atlantic managed to overflow the land bridge at Gibraltar. It started doing this around 6 million years ago, and did it again and again for the next 630,000 years. Each time, it deposited vast layers of salt and other minerals at the bottom of the Mediterranean basin (hence, the term salinity crisis), then covered them over with silt when the basin refilled.
The last of these episodes of the great drying out was apparently the longest and most complete. For 260,000 years, the Mediterranean basin was almost empty of water, despite the rivers that continued to feed into it. Finally, 5.33 million years ago, a small but growing river that flowed past Gibraltar from the Atlantic, managed to erode a channel big enough to reach a tipping point. To be clear, it may have taken a thousand years to do that, but once it did, the Atlantic catastrophically flooded in, with a maximum flow more than 600 times that of the Amazon (which itself is more than 70 times the flow of the Nile), gouging the channel past Gibraltar so deeply that it never closed again. It’s estimated that once that process started, the Mediterranean went from 10% full to completely full in less than two years.
The Mediterranean holds 900,000 cubic miles of water (3.75 million cubic kilometers). What happens if you evaporate nearly all of that and rain it back into the rest of the world’s oceans? You get something like a 30-foot rise in world sea level. That’s how far the world ocean would have dropped when the Mediterranean refilled, and most of the refilling and most of the drop happened in less than two years.
I thought of that a few years back, when Michael Griffin, appointed by President Bush as administrator of NASA, said this on NPR’s Morning Edition (May 31, 2007):
I have no doubt that … a trend of global warming exists. I am not sure that it is fair to say that it is a problem we must wrestle with. To assume that it is a problem is to assume that the state of Earth’s climate today is the optimal climate, the best climate that we could have or ever have had and that we need to take steps to make sure that it doesn’t change. First of all, I don’t think it’s within the power of human beings to assure that the climate does not change, as millions of years of history have shown. And second of all, I guess I would ask which human beings — where and when — are to be accorded the privilege of deciding that this particular climate that we have right here today, right now is the best climate for all other human beings. I think that’s a rather arrogant position for people to take.
Honestly, the mind just boggles. I mean, this guy was put in charge of NASA. (Granted, having a NASA administrator who would say things like this was a big part of why he was put there.) But okay, fine. Let’s do a little thought experiment, shall we?
Suppose an alternate history. The Mediterranean never permanently refills, but human beings nevertheless evolve, and eventually develop a global civilization, arranged differently around the world, to be sure, but equivalent to what we have now.
Now suppose a bunch of folks start doing something at the western edge of the nearly empty Mediterranean basin that makes them immensely wealthy, but poses a very high risk of accidentally breaching the Gibraltar barrier and initiating an unstoppable flood.
When other folks notice this and object to it, somewhere on that alternate Earth a clone of Michael Griffin pipes up and says, “Well, the Mediterranean Basin has flooded in the past, and if some natural process were to cause it to flood again, we certainly couldn’t stop it. And anyway, who’s to say whether that world would be worse than this one? After all, trade between Europe and Africa would get a lot easier, wouldn’t it? I think it’s rather arrogant for certain people to claim for themselves the privilege of deciding that the world as we know it is the best one for the rest of us.”
Meanwhile, the whole basis of alternate Michael Griffin’s civilization—the location of its coastal cities, continental shelf fisheries, great farming regions, shipping and transportation routes, the homes and livelihoods of billions of people—all depend on a sea level 30 feet higher than ours, with all the coastlines, rainfall patterns, ocean currents, and regional climates that go with it.
It has been millions of years since our atmosphere had 400 parts per million of CO2—a level it has once again reached, thanks to us. The last time it was this high, there was no ice at all on Greenland, or on a good chunk of Antarctica besides. Sea level was dramatically higher, as a result. It was a lot hotter, too.
Of course, if you turn up the thermostat in a cold house, it doesn’t hit the new setting bang! like that. It takes time to get there. The scientific big picture here is not even slightly in dispute. The more carbon dioxide there is, the hotter the atmosphere will be when it finally hits the new setting. What working climate scientists quibble about these days are the details. How long will it take to finally stabilize at the new average global temperature? Exactly how much hotter will that be? How much of North America will routinely experience highs of 100º F or more for half the year? How much Antarctic ice will be left? What will sea level be? How much of Florida and the Mississippi Valley will be under water? Will there be any of Bangladesh left at all?
We’re not even turning up the thermostat to some unknown temp and leaving it there. We keep setting the knob higher. We’re dumping an additional 35+ billion tons of CO2 into the air every year.
If we don’t get off fossil fuels fast enough, if we really do go too far, well, with enough time and resources, and if our civilization doesn’t come totally unglued in the process, we might move all our endangered cities tens or hundreds of miles inland, or out of once fertile areas that have turned to dust; move our agriculture into the new temperate regions of Canada and Siberia; get past the coming wars over access to dwindling ground water and build desalination plants everywhere; relocate billions of people in the process, including out of regions where outdoor summer heat has become routinely deadly; and if we’re really lucky, find alternatives to all the seafood species we used to rely on for so much of our protein, that aren’t there anymore because their food chains collapsed when the plankton they depend on couldn’t evolve fast enough to survive what all this was doing to their seawater.
Maybe we could succeed in this, but at what cost, for something that never had to happen in the first place? If someone torches your house, burns it to the ground, you might be able to rebuild (if you can afford it), but you’ll never get those things back, and it’s not as though you had nothing better to do with what they’ve stolen from you.
I don’t know how this cannot be obvious.
The point is not that the climate we have is “the best climate” for everyone, whatever that even means. The point is that this is the climate to which the whole of our civilization is adapted because this is the climate we have.
The entire history of civilization, all of its development, has taken place within this global climate which, notwithstanding a few minor ups and downs, has been stable since the end of the last ice age 10,000 years ago. Adjusting to something so seriously different will be unspeakably costly, and unconscionably painful, especially for the countless generations not yet born who had no say at all in trashing the world we’d be leaving them. If we do that to them and they look back and ask why, the answer will be that we allowed a few staggeringly wealthy people, wealthy beyond the wildest dreams of the vast majority of human beings who have ever lived, wealthy far beyond any legitimate need for material possessions, to keep us addicted to sources of energy they controlled, so they could continue to rake it in. The word for that? Immoral.
It doesn’t have to be that way. That’s the point. We stumbled into this blindly, by accident. What we are doing to the earth’s climate is not obvious; it is unbelievably subtle, it cannot be directly perceived, and truly, it is one of the greatest triumphs of science that we know about it at all. We have a duty to not squander that knowledge.
We have been given a profound gift: the ability to discover, just soon enough, what is happening, to understand that we are the cause, and to do something about it. We’re setting ourselves up for changes that will severely disrupt our entire world. There are hopeful signs out there, but we are already uncomfortably close to being too late to avoid a whole lot of trouble.
It’s time to stop spouting nonsense, take responsibility for the consequences of our actions, and conceive less disruptive, genuinely better ways to live our lives.