Fascinating article in the June 23 issue of Science. A major puzzle of paleoclimatology is why after tens of thousands of years of glacial conditions, recent ice ages have ended with relatively sudden warm ups. Six authors have devised a comprehensive hypothesis as to why. Here is my attempt to summarize the process:
If this research holds up to scientific scrutiny, it will bear on the current global warming debates. Some have interpreted the rise of carbon dioxide in the atmosphere at the end of the last ice age not as a cause of deglaciation but rather as an effect of deglaciation. These six authors see carbon dioxide as playing a key role in finally bringing to an end the last ice age because carbon dioxide is a greenhouse gas.
Courtesy RrrrredHey, Buzzketeers. I’m going to be straight with you up front (I always am):
I haven’t actually seen “The Day After Tomorrow,” even though it will feature prominently in this post. I did see the preview, however, and I know the title, so I’m confident that I can sum the film up pretty accurately.
The is how The Day After Tomorrow goes, more or less:
The kid from Spiderman, Peter Parker, is a young scientist trying to make a name for himself in the big city. He has a crippling fear of wolves. Trying to be a famous scientist, however, is a lot like trying to be a Hollywood celebrity: there are a million other kids out there just like you, except that some of them are better looking with bigger muscles, or more feminine ankles, so you have to be willing to act a little crazy, or go on camera naked.
Peter Parker, fortunately, opts for the “act a little crazy” route. He soaks up a couple red bull-vodkas and starts researching. After 7 panicked days and 6 insane nights, Peter says, “Check it out! The Day After Tomorrow, the poop is really going to hit the fan!” But the scientific community was all, “Whatever, Parker. Take that shirt off, and let’s get you on camera.” They were so preoccupied with the thought of Peter’s scientist muscles that they failed to realize that he was right! Like two sick bears squatting on an airboat, the poop was really about to hit the fan.
Sure enough, Peter Parker’s discovery proved to be accurate. The planet’s ocean currents went all haywire, and a couple days later things got really cold and stupid. Peter Parker, despite being shirtless at this point, was more prepared for the situation than everyone else, and he grabbed a sled and went to rescue a friend of his, possibly a beautiful woman or man, who was trapped in an elevator behind some very impressive icicles. Along the way, Peter had to avoid the many wolves that immediately moved into the frozen cities in search of delicious, un-canned human food, but once he rescued his beautiful friend the wolves could no longer be dodged. After a 45-minute-long wolf-fighting scene, Peter emerged bloody and victorious. He had truly conquered this world of the day after tomorrow!
It’s a little silly isn’t it? I mean, everyone knows that ocean currents are vital for spreading heat across the planet, and moderating higher latitude climates. Duh. Surface water is warmed in the tropics, and is pushed into currents by regular wind patterns and the rotation of the Earth. As it reaches colder seas, the water releases heat and moisture into the atmosphere. Colder and saltier now (because the salt in water doesn’t evaporate), the water is denser, and it sinks down to join deeper currents, where it will flow thousands of miles around the planet, before eventually returning to the tropics to be warmed again. Tada. And, of course, shortly after the end of the last ice age, a huge, cold, freshwater glacial lake burst its shores and spilled into the north Atlantic, halting this water cycle and disrupting the Gulf Stream current to plunge the Earth into another thousand years of coldness. But that sort of thing couldn’t happen the day after tomorrow, could it? Noooo. We all know that. It would take years for such a tremendous change in climate to occur. What a silly movie.
Or… maybe not. A new study from the University of Saskatchewan suggests that the story of Peter and the Wolves may not be as far fetched as we all thought. Based on lake core samples, the research seems to indicate that the drastic cooling, at least in Europe, could have occurred over a period as short as just a few weeks, not over the space of years, as was previously accepted.
Lake cores are samples of the deep mud and sediment at the bottoms of lakes, and they’re surprisingly useful for telling what happened above a lake a long time ago. Think about it—if things got really windy, for example, lots of dust and dirt would be blown onto the lake, and it would eventually settle down to the bottom, forming a unique layer. Or if all the plants nearby died suddenly, you’d probably see less pollen in the layer deposited at that time. Scientists can even look at the isotopes of the atoms in lake core layers to learn about what was happening at the time—carbon isotopes can show how much stuff was alive in the lake, and oxygen isotopes can indicate local temperature and rainfall. Examining cores from a very old lake in Ireland, the researchers discovered that the transition to the Younger Dryas period (the sudden return to ice age-like conditions) happened very suddenly, perhaps in as short a time as a month. Peter Parker was right! Peter Parker was right!
As I understand it, though, this rapid and severe change hinges on the North Atlantic Current (the Gulf Stream) being totally shut down very quickly. Cold fresh water released by melting icecaps could very likely affect weather patterns, but something on this scale would require a fairly catastrophic event—some scientists suggest that the Younger Dryas could have been triggered by some sort of extra-terrestrial impact, although the theory is heavily debated.
Still, if some hot young scientist approaches you with some hot young ideas, don’t immediately insist that he take his shirt off—he might be saying something worthwhile
It could always be worse.
Some geologists think that 700 or so million years ago, the entire earth was one spherical skating rink. Called "Snowball Earth", it was a time when runaway ice caps covered the entire earth. They even covered the tropical oceans, making a mid-winter getaway to Hawaii less appealing, and possibly wiping out most of life on earth. The theory goes like this. Millions of years ago the sun was weaker than today. Ice started forming at the North and South poles, reflecting incoming sunlight back out to space and making it colder. So, the ice grew even more and so on in something called a positive feedback. Eventually, ice covered the entire planet, leaving rock types characteristic of glacial erosion in the tropics.
So, how do they think we got out? Well, all the time the earth was covered with ice, volcanoes were belching out carbon dioxide. Over millions of years, carbon dioxide is sucked out the atmosphere by breaking down rocks (it's much too slow a process to help us out in the current situation, though). Eventually carbon dioxide levels in the atmosphere reached many times what they are today, temperatures soared, and there was a global ice-out that's usually described as "catastrophic."
A careful review of the existing information by two scientists from Britain suggests that things may not have been so dire. Geological evidence suggests that some parts of the ocean were not covered in ice, though there was a lot of ice in the tropics. This new view means geologists and climate scientists need to re-think "Snowball Earth" and how it could have come about. Something to think about while you're trying to get the car started.
At 9,500 years old, it took root just after the last Ice Age. It can tell us a lot about the climate at the time, and how the Earth has changed over thousands of years. (The previous oldest-known trees are North American bristle pines – at 5,000 years old, mere saplings to the Swedish spruce.)
It was commonly believed that mammoths died about some 12,000 years ago due to over hunting by the growing human population on the planet. But cutting off of the intercontinental bridge between Asia and North America made have been the main culprit.
Paleontologists from England studying the lifecycle of mammoths now believe that inbreeding and a lack of genetic diversity probably played the biggest role in knocking down mammoth populations. Here’s the quick mammoth timeline:
About 150,000 years ago the huge hairy elephants emerged on the scene in Asia. Some of them migrated across to North America over the land bridge that was open at that time between what is now Russia and Alaska.
Warming of the Earth raised ocean levels and cut off that land bridge, creating two distinct herds of mammoths on the each continent. For a brief time around 100,000 years ago, that land bridge came back, and the herds were able to intermingle again, but rising oceans again cut off the two groups.
With fewer genetic improvement options with the limited size of the herds, the mammoths weren’t able to adapt as quickly when another Ice Age hit some 20,000 years ago. They were able to hang on for another 8,000 years or so before becoming extinct.