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Sunday, June 13, 2004

Doubling the length of the ice core record of past climate... 

A consortium of european researchers have just published the preliminary steps in an analysis of an ice core recovered from Dome C in the East Antarctica (here's the paper, for which you will need a subscription to the journal Nature, and here are two perspectives on the work for which you may not). The core, over 2900 meters long so far, is notable because it extends the ice core record of past climate back from ~400,000 ybb (the current oldest ice from a core drilled at the Russian Vostok station in the East Antarctic) to ~750,000 ybp

But why is all this important? In general ice core records of the variability of past climate are valuable because they contain high resolution records of past temperature (through the variation in the isotopic composition of the ice), high resolution records of the composition of past rain water (such measurables as the ionic content of the ice), as well as samples of past atmospheres (through bubbles trapped in the ice near the surface). Ice sheets and glaciers are thus the best way we have of looking at past climates sufficiently finely in time to allow testing dynamical models of how climate works and to understand the extent to which climate may vary in the absence of human interaction.

The gist of the new portion of the record is that much of the variability in the older ice looks alot like the variability in the younger (before the influence of humans). In general the major difference appears to be that warm episodes (called interglacials) don't get as warm before 450,000 ybp, but tend to last for longer (so the avg temperature is ~the same).

The authors of the paper make the argument that the ~28,000 year period from 430,000-402,000 ybp (the first really good look at which comes from this core) is the most analogous to the Holocence (the last 14,000 years or so in which all of human history has occured and the climate has been stable enough to allow agricultural development) and therefore infer that, if humans haven't screwed things up, we might expect another 14,000 years or so of climate stability before the next ice age.

It is key to note, however, that the real point of this paper is that humans have screwed things up. We already knew that the greenhouse gas concentrations of the atmosphere are much higher (2x - 5x depending on the species) now than they have been at any time in the last 400,000 years. We now know that this is equally true of the last 750,000 years. What exactly this means for us, and what we do about it, are still open questions.
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