The question was so deep that almost no one had thought to ask it before: Does a climate exist? That is, does the earth’s weather have a long-term average? Most meteorologists, then as now, took the answer for granted. Surely any measurable behavior, no matter how it fluctuates, must have an average. Yet on reflection, it is far from obvious. As Lorenz pointed out, the average weather for the last 12,000 years has been notably different than the average for the previous 12,000, when most of North America was covered by ice. Was there one climate that changed to another for some physical reason? Or is there an even longer-term climate within which those periods were just fluctuations? Or is it possible that a system like the weather may NEVER converge to an average?
This is from James Gleick’s excellent book Chaos. Earth's climate (at least as it was understood at the time Gleick wrote Chaos) is non-stationary. It doesn't have a long term average, and as the excerpt implies one epoch's "average" climate can be very different from another's. Like a random walk, it doesn't settle on or revert to a long term average value. The book contains a reference to this paper from 1964, to flesh out some of the details. I don't know how much or how fast the Earth's climate changes due to these endogenous drifts (as opposed to forcings like CO2 or aerosols), but it seems like this should color our view of climate change somehow.
I wonder of Gleick would feel uncomfortable writing that paragraph today. The climate of intellectual thought has indeed drifted to a different regime, and some of these basic points about the history of climate science might not be welcome. There is a discussion in Chaos of Earth getting "kicked" into a very different climate and getting stuck in that equilibrium. But it's not the "Venus Earth" scenario or even a very much warmer but still livable Earth. Rather, early climate modelers believed, based on their computer generated scenarios, that a "White Earth" was possible: an Earth in which the oceans are all covered in snow and the continents with ice. Climatologists were scratching their heads that their computer simulations kept falling into this scenario, but the real Earth never seems to have switched to this regime.
Don't read me as having some kind of hidden meaning or implication here. I'm just sharing because I found it interesting. Chaos is well worth a read.
I wonder of Gleick would feel uncomfortable writing that paragraph today. The climate of intellectual thought has indeed drifted to a different regime, and some of these basic points about the history of climate science might not be welcome. There is a discussion in Chaos of Earth getting "kicked" into a very different climate and getting stuck in that equilibrium. But it's not the "Venus Earth" scenario or even a very much warmer but still livable Earth. Rather, early climate modelers believed, based on their computer generated scenarios, that a "White Earth" was possible: an Earth in which the oceans are all covered in snow and the continents with ice. Climatologists were scratching their heads that their computer simulations kept falling into this scenario, but the real Earth never seems to have switched to this regime.
Don't read me as having some kind of hidden meaning or implication here. I'm just sharing because I found it interesting. Chaos is well worth a read.
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