Gazing into my crystal ball, I see ...
Ice.
You've probably seen the movie, The Day After Tomorrow, a mega disaster, end-of-the-world special effects extravaganza. Many people don't realize that it was based on the book, The Coming Global Superstorm.
Here's a blurb from Wikipedia:
The book posits the following theory:
* First, that the Gulf Stream and North Atlantic drift generates a cordon of warm water around the north pole, which in turn creates a cordon of warm air that holds in a frozen mass of arctic air.
* Second, that if the Gulf Stream were to shut down, that barrier would fail, releasing a flood of frozen air into the northern hemisphere, effecting a sudden and drastic temperature shift.
The book discusses a possible cause of the failure of the gulf stream: that the melting of the polar ice caps could drastically affect the salinity of the North Atlantic drift by dumping a large quantity of freshwater into the world's oceans.
The disaster they're talking about is this: The upper atmosphere's frozen air suddenly comes crashing down and instantly flash freezes everything in the northern hemisphere.
The book says this may have happened in ages past, as part of a larger climate cycle we know little about, and that the effects of man-made global warming are hastening the process in the current cycle. You know those flash-frozen green beans in the freezer? Well, it may be that Mother Nature flash froze some woolly mammoths a while back. They were unearthed thousands of years later with fresh food still in their mouths and undigested food in their stomachs. The article I've linked to gives the standard explanation that they "may have been trapped in bogs or quicksands and either died of starvation or exposure, or drowning if they sank under the surface. Though judging by the evidence of undigested food in the stomach and seed pods still in the mouth of many of the specimens, neither starvation nor exposure seem likely."
The movie depicts the same flash-freezing happening to humans and everything else.
So, how could the frozen air in the upper atmosphere suddenly come crashing down and instantly flash freeze every single green bean and human in the northern hemisphere? It's the "cordon of warm air" which prevents that from happening now. But if the air in the barrier is no longer warm, then the super-cold air slams to the earth (remember, warm air rises, cold air falls.)
The warm air barrier exists because of the "conveyor belt" effect of the Gulf Stream and North Atlantic Drift. The Gulf Stream's warm water is pulled northward by the North Atlantic Drift. The warm water sits atop the cold water of the Drift. The evaporation of this warm water as it drifts north warms the air, and thus, most of Europe (remember, England is at the same latitude as Canada, yet it is considerably warmer.) Simultaneously, the further north the warm water travels, the colder it gets. As it cools, it sinks (warm water rises, cold water sinks.)
This cycle of warm water evaporating and warming the air, then cooling and sinking as it travels north, and traveling back down to the Gulf, is called thermohaline circulation. Everything works fine as long as nothing drastically interferes with this cycle.
The disaster in the movie is caused by the shutdown of thermohaline circulation. If it shuts down, then warm water is no longer carried from the Gulf Stream to the North Atlantic Drift because the Drift is no longer circulating. No warm water means no evaporation to warm the air. Instead, only cold water is evaporating, cooling the air. No warm air means no barrier to keep the super-cold frozen air aloft. The super-cold air has nowhere to go but ... down.
What caused the hypothetical shutdown of thermohaline circulation in the movie? A change in seawater density. If you alter salty water by adding freshwater, you change the water's density. Freshwater is less dense than salty water, so it stays on top. What caused the massive influx of cold freshwater into the ocean's seawater in the movie? Melting glaciers.
Of course, that was just a movie, and we don't have anything to worry about. Unless the glaciers start melting. Oh wait. They are.
Unlike the book, the movie didn't take into account what would happen if vast amounts of trapped methane were released into the atmosphere.
Methane is the byproduct of decaying plants. In bodies of water, the gases produced by the decay process can't rise to the surface because the water is too dense. The water keeps the methane trapped.
Runaway Methane Global Warming
This anaerobic decay produces methane which gets trapped in the silt as methane hydrates until the conditions of water temperature and pressure change which can release the methane in vast quantities very quickly. Another form is a frozen slush/ice methane hydrate where the methane is trapped in an ice/water mixture which releases the methane when it warms up or the pressure on the ice is reduced. Frozen methane hydrates can contain 170 times their own volume of methane. These frozen hydrates occur in the seabed deposits of the Arctic Ocean.
The same thing happens in the ground in permafrost.
Methane can also be trapped by permafrost layers which over-lay lower unfrozen layers of vegetable material that is decaying and producing methane which remains trapped by the frozen permafrost on top. If the permafrost layer were to melt then the methane in the layers below would escape into the atmosphere. Given the vast areas of permafrost in northern latitudes there is a significant potential for methane to be trapped that would be released if the permafrost melted as a result of global warming.
Well, it's a good thing the permafrost isn't melting. Oh wait. It is.
Well, have a nice day, everyone.
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