Lunar dawn on a primeval earth. Image by Karen Werhstein, used with permission.
If you read astronomy sites as much as I do it would be easy to come away thinking the earth is smack dab in the center of something called a Goldilocks Zone. Technically it just means the distance from a star where water can exist on the surface of a planet as a liquid. Not too hot like Venus, not too cold like Mars. But this can easily be confused with perfect and truth be told, our planet coalesced just a bit too far out, a little too close to the cold side of the zone. Going by the influx sunlight on a spinning globe alone, the surface of the earth could be frozen solid. In fact there's good evidence that it has been frozen solid from pole to equator more than once over the last four billion years.
There's a number of factors that keep the earth from being a permanent snowball. One of the big ones is our sun, it's slowly heating up, about 5 percent to 10 percent every billion years. The other big one is the earth is not a barren ball of rock, we have oceans and snug blanket of air which soak up solar energy when the sun is out and distribute it more evenly around the planet 24/7. In the end, these two factors, which have preserved life and may have literally saved the entire biosphere from icy extinction will eventually roast and sterilize the entire planet until it's deader than fried chicken. Best estimates? That probably won't begin in earnest for roughly one billion more years. Unless of course our estimates are off, and especially if we were to offer a big fat assist in roasting the planet, you know, to make a few bucks for a few already super wealthy people. It could start with a burp, a burp of freedom!
More on the snowball earth below the fold.
If we could go back to the Cryogenian period, beginning about 850 million years ago, earth would have more resembled the fictional ice-planet Hoth in Star Wars. Except for the atmosphere, which would have supported neither tauntaun nor rebel alliance, as it probably consisted mostly of nitrogen with no oxygen at all. Evidence shows this was the most extensive and severe series of glaciations our planet has ever known. It's widely believed that some of the glaciers may have extended all the way to the equator, meaning the earth was sheathed in ice from pole to pole, across ocean and land.
Models show the snowball earth is an incredibly stable state. Left alone, huge amounts of sunlight is reflected by the ice and snow back into space, zero humidity means very little cloud cover. The snowball is an end point, with no escape. Except obviously there was or we wouldn't be here.
There is one set of phenomena the snowball wouldn't affect: Geological processes like thermal vents, volcanoes, geysers and the like would continue uninterrupted. With almost no rainfall and little in the way of weather, any greenhouse gases released by those hot spots would hang around a long, long time. Long enough to accumulate. Once they reached a certain threshold, the temperature at the equator would begin to tip above the freezing point of water, after that, watch out! Water absorbs way more sunlight than ice, it would heat up and melt more ice, and the cycle would run away with itself, faster and faster.
Models show the amount of time from the first narrow leads in the ice developing around the equator to an earth completely ice free, could have occurred in as little as 100 years, with almost half of the melting coming in the last decade! During which time the average global temperature could easily skyrocket a whopping 100 degrees Fahrenheit. It would have been about as a dramatic a climate transformation as our world has ever undergone, from clear alpine white snowball earth under crystal clear blue skies, to steamy ocean planet shrouded in thick rain clouds under which long lasting category six or seven supercanes and super cells spawning F-10 tornadic vortices churned the seas and scoured the land. This cycle of icy boom and bust appears to have happened more than once.
But eventually the Cryogenian ended and gave way to the Ediacaran, which gave way to the more famous Cambrian, and the rest is natural history. Here we are.
Today we have permanent ice caps on both poles, probably an unusual state of affairs over the last half billion years or so. The primary agent keeping the planet cool enough to keep those global air-conditioners running is likely the geographic and thermal isolation of Antarctica. But the sun is hotter now than it was when the Cryogenian started, all the earth needs is fuel for a tipping point to lose those ice caps. And over the last few hundred million years that fuel has been laid down in thick deposits all over the poles and into the temperate boundaries surrounding them. That fuel may be about to light up, a new study suggests the near term cost could reach a staggering $60 trillion dollars, the long term effects could be literally apocalyptic:
Billions of tonnes of the greenhouse gas methane are trapped just below the surface of the East Siberian Arctic shelf. Melting means the area is poised to deliver a giant gaseous belch at any moment - one that could bring global warming forward 35 years and cost the equivalent of almost a year's global GDP.
These are the conclusions of the first systematic analysis of the economic cost of Arctic melting, which delivers a sobering antidote to other, more upbeat assessments that say melting in this area would improve access to minerals on the ocean bed, increase fishing and create ice-free shipping lanes.
That's just the East Arctic Shelf, there are megatons of methane stored elsewhere in both landlocked permafrost and
methane hydrates at the bottom of the world's ocean. Once any of it gets belched into the atmosphere in quantity we may see a runaway feedback loop, melting more ice and tundra, leading to more methane release and more absorption of sunlight, all the way to the grim end: a steamy stormy ocean planet with no cryosphere to speak of marked by raging, rising water driven by long lasting hurricanes and tornadoes over land and sea.
How fast could that happen? We simply don't know. It might not happen at all, or could take millennia to develop, or it could virtually explode into that state given the right kick and forced onward by a sun now substantially hotter than it was 850 million years ago. And apparently we should not try to stop this. Because ... freedom ...?