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Something Cool, Way Cool
The Earth >
We've just passed the annual Beginning of Summer. For many people that signifies a dive into hotter temperatures and little to no rain.
But it could be worse --- a lot worse.
Most of us remember from school that the Northern Hemisphere experiences its greatest tilt toward the sun around June 21. The more direct sunlight and longer daytimes can make it pretty warm. But it's more than the tilt at work here.
The more scientists look, the more they see several of Earth's orbital properties all simultaneously playing a significant role in our climate caper. And the deeper they look, the more complicated --- and wonderful --- it gets. First, let me introduce the latest suspects:
Suspect #1: Tilt. The Earth isn't always tilted over 23.5 degrees. It varies, over tens of thousands of years, from 22 to 24 degrees --- a seemingly minor change. The Moon and other planets play the significant role in steadying it.
Suspect #2: Eccentricity. Eccentricity refers to how circular an orbit is. An eccentric orbit is a form of stretched circle, similar to an oval, taking a planet alternately closer and farther from the sun during its year. Our eccentricity is remarkably small, varying by only millions of miles. Earth's orbit ranges from very nearly circular to just slightly more eccentric over a100-thousand-year cycle --- a seemingly minor change.
Suspect #3: Precession. In your mind's eye picture a top spinning. Eventually it sort of wobbles, doesn't it? So does our planet. Only it takes 26000 years to wobble just once --- a seemingly minor change. Stick around for another 13000 years and, assuming we don't mess with the calendar, you'll find that during June we'll be tilting away from the sun.
A hundred years ago a man named Milutin Milankovitch looked at these suspects and suspected they were all three conspiring to dictate our planet's climate. He proposed that great worldwide climate changes --- like ices ages - were due not just to our obvious tilt, but also to how our orbit was behaving, and in what direction we were wobbled at the moment.
An exaggerated example might help here. (Thinking cap time!)
The Northern Hemisphere has a lot of landmass that can get all glaciered up and iced-over. What if the Earth happened to be at maximum tilt at the same time the eccentricity was at its greatest? And what if the land-stuffed Northern Hemisphere of our planet was that hemisphere tilted away when Earth was furthest from the sun in its orbit?
It would get pretty darn cold up here, that's what! It would be Glacierville! And summers, such as they were, wouldn't be long enough to warm the place up. After years of this --- ba-da-bing! --- you've got an Ice Age!
This is called the Milankovitch hypothesis. And here is the positive spin on it all ...
If this theory proves correct, you, dear reader, are living at the time when the three cycles are balanced very nicely allowing not too much, not too little, but just the right amount of solar radiation to strike Earth, making the world's climate pretty comfortable overall. No ice age or oven temperatures for us!
Not only are we in a perfect galaxy in a perfect part of the universe, with the perfect solar system and planet, it also appears that even the "seemingly minor” aspects of Earth's orbit are balanced and coordinated and fine-tuned so that we all have a pretty nice place to live. What are the odds?!!
Enjoy your summer while you can. In just thousands of years, it will be a lot different.
Mark Ritter can be reached here.
Posted by Administrator at 2002.06.22 02:46 PM | Comments (0)
