Wednesday, March 16, 2005

The global warming hockey stick

The BBC carries a report today that reveals a split in the scientific community (now there's a thought) concerning the use of statistics to support a theory. In this case it is the "hockey stick" graph that appears to demonstrate a rapid increase in (?anthropogenic) global warming since 1900. Here's the graph:

Several points are worth commenting on about this graph. The first is that the rapid increase in temperature since 1900 is based on instrumental data whereas older data is based on inferred observations. Nowhere on the pre-1900 portion of the graph can be seen the "mini ice age" that occurred between 1600 and 1850 AD. This was a time when winters were extremely severe with the tidal River Thames freezing over frequently. Going back in time the Medieval Warm Up period (800 to 1400 AD) also doesn't show up with any statistical significance.

But what everyone seems to be missing is the fact that this graph, as complex and scientific as it may appear, only represents a very brief span of geologic time. We have 1000 years of history on the graph. That's a long time relative to a human lifetime but in the context of Nature it is extremely short. The Pleistocene (Holocene) Period, which basically covers the span of the most recent ice ages, lasted 1.7 million years. During that time four major episodes of ice development occurred. Here is a good article about the ice ages that actually suggests we could plunge into a fifth ice age at any time, regardless of "global warming trends". Food for thought.

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