Ice core data

Great ice core data and graphs at The Foresight Institute:

I’m looking at the temperature record as read from this central Greenland ice core. It gives us about as close as we can come to a direct, experimental measurement of temperature at that one spot for the past 50,000 years.  As far as I know, the data are not adjusted according to any fancy computer climate model or anything else like that.

So what does it tell us about, say, the past 500 years? (the youngest datum is age=0.0951409 (thousand years before present) — perhaps younger snow doesn’t work so well?):

histo6

Well, whaddaya know — a hockey stick.  In fact, the “blade” continues up in the 20th century at least another half a degree.  But how long is the handle? How unprecedented is the current warming trend?

histo5

Yes, Virginia, there was a Medieval Warm Period, in central Greenland at any rate.  But we knew that — that’s when the Vikings were naming it Greenland, after all.  And the following Little Ice Age is what killed them off, and caused widespread crop failures (and the consequent burning of witches) across Europe.  But was the MWP itself unusual?

histo4

Well, no — over the period of recorded history, the average temperature was about equal to the height of the MWP.  Rises not only as high, but as rapid, as the current hockey stick blade have been the rule, not the exception.

histo3

In fact for the entire Holocene — the period over which, by some odd coincidence, humanity developed agriculture and civilization — the temperature has been higher than now, and the trend over the past 4000 years is a marked decline.  From this perspective, it’s the LIA that was unusual, and the current warming trend simply represents a return to the mean.  If it lasts.

histo2

From the perspective of the Holocene as a whole, our current hockeystick is beginning to look pretty dinky. By far the possibility I would worry about, if I were the worrying sort, would be the return to an ice age — since interglacials, over the past half million years or so, have tended to last only 10,000 years or so.  And Ice ages are not conducive to agriculture.

histo1

… and ice ages have a better claim on being the natural state of Earth’s climate than interglacials.  This next graph, for the longest period, we have to go to an Antarctic core (Vostok):

vostok

In other words, we’re pretty lucky to be here during this rare, warm period in climate history.  But the broader lesson is, climate doesn’t stand still.  It doesn’t even stand stay on the relatively constrained range of the last 10,000 years for more than about 10,000 years at a time.

This doesn’t mean CO2 isn’t a greenhouse gas.  It just means the wisest course of action is a gradual one.

It also suggests that those who argue that it’s an unprecedented crisis demanding unprecedented action, including surrendering liberty to watermelons and national sovereignty to corrupt international institutions, might have a hidden agenda…

UPDATE 4/6/10:

Bret Stephens launches a new contest in today’s WSJ: predicting the next green panic.

The world is now several decades into the era of environmental panic. The subject of the panic changes every few years, but the basic ingredients tend to remain fairly constant. A trend, a hypothesis, an invention or a discovery disturbs the sense of global equilibrium. Often the agent of distress is undetectable to the senses, like a malign spirit. A villain—invariably corporate and right-wing—is identified.

Then money begins to flow toward grant-seeking institutions and bureaucracies, which have an interest in raising the level of alarm. Environmentalists counsel their version of virtue, typically some quasi-totalitarian demands on the pattern of human behavior. Politicians assemble expert panels and propose sweeping and expensive legislation. Eventually, the problem vanishes. Few people stop to consider that perhaps it wasn’t such a crisis in the first place.

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