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Sunday, March 6, 2011

Think it's getting hot?

Over the past 100 million years, Earth's temperature was hotter than it is now about 97% of the time.

Ice ages began in earnest 1 million years ago. (Earlier episodes of glaciation also occurred.)

In the past 1 million years, in what we call the Quarternary Ice Age, we have had advances of ice every 100,000 years. We are currently in an interglacial period of the Quarternary Ice Age.

Only 10,000 years ago, while Earth was warming from the last Ice Age, a partial new ice age began that lasted only 1000 years. (It was called the Younger Dryas.)

At the end of that 1000 years, about 9000 years ago, the temperature rose quickly and Earth was hotter than it is now.

It's cooled off slightly since then, and we are enjoying a nice stable warm period, more stable than any in the past few million years.

Since 9000 years ago we have gone through several warming and cooling cycles with smaller ups and downs than the earlier spikes. The most recent of these is the 'Little Ice Age' of about 1300-1850 AD.

We're still warming from the Little Ice Age but have not reached the warmth of 9000 years ago.

What's next? Looking at the past, the best answer is more cooling, and sooner or later another ice age. How man's activities might change that - if man could come close to changing such powerful cycles - is unknown.

For more information about temperature variations on Earth, see: Ice Ages and Interglacials by Donald Rapp, The Little Ice Age by Brian Fagan, and Frozen Earth by Doug Macdougall.

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