Thursday, December 08, 2005

Hottest Year "On Record"

This piece proclaiming that 2005 is the hottest year "on record" has run right into one of my pet peeves, which is that where climate is concerned, "the record" doesn't mean much. "The record" refers to directly observed temperatures and those only go back 150 to 200 years at the most. At the time scale that our planet's climate operates, that means very little. It's like taking a range of temperatures over 15 minutes in one particular day, and attaching great significance to the "record" high temperature you found.

I borrowed this chart from the LA Times a few weeks ago and it is a good illustration. Frankly, I think all that this really tells anyone is that in 1878, Los Angeles was a small town with no paved roads and in 2005 it is a paved-over megalopolis with lots of concrete and asphalt that holds heat.

Climate cycles are multiple centuries long. We know this because of indirectly observed temperatures based on what is called proxy data. Hundreds of climatologists all over the world gather data from tree-rings, ice cores (oxygen isotope ratios), pollen from soil cores, microfossils from deep sea cores, etc. that tell them what temperatures were over ranges of hundreds of thousands of years. This book tells you all about those techniques. They give you useful, long-range charts like this one.

This chart shows a range of temperatures for the last 400,000 years above and below the average for the last 100 years based on proxy data from an ice core in Antarctica. The spikes indicating higher temperatures show the interglacial periods like the one we are in now. The lower readings indicate the cool glacial periods. Looking at this chart shows that to be entirely accurate, 2005 can't be the "hottest year on record", in fact there are probably hundreds of years in the last three interglacials that were hotter than 2005.

It irritates me that climate scientists like the one who gave the "hottest year" press release I linked to above, know this perfectly well. It gives me the impression that they aren't being entirely honest.

1 comment:

Matt Mullenix said...

Excellent point, Reid, about the heat island effect and your mention of LA's growth during the years on record. I've often wondered about that. Probably most longterm temperature readings are compiled in cities, always hotter than fields and forests; and they get hotter as they get bigger. Atlanta's heat island history over the last two decades offers the "fast forward" view.