White Earth Climate

Looking at the idea of a climate equilibrium, I came across this and wish I had paid more attention to Gleick:

“Their natural bias is to make models with a strong tendency to return to the equilibrium we measure every day on the real planet. Then, to explain large changes in climate, they look for external causes—changes in the earth’s orbit around the sun, for example.” – James Gleick

Hansen & Lacis took this approach in 1984 I think. It has been said that CO2 is only thing that makes the GCMs work. I think there is a bias towards looking for external causes.

“Climatologists who use global computer models to simulate the long-term behavior of the earth’s atmosphere and oceans have known for several years that their models allow at least one dramatically different equilibrium. During the entire geological past, this alternative climate has never existed…”

The White Earth equilibrium. Lots of snow and sea ice.

“Then, for no reason whatsoever, it shifts into a different sort of behavior, still fluctuating but producing a different average. The people who design computer models are aware of Lorenz’s discovery, but they try at all costs to avoid almost-intransitivity. It is too unpredictable.”

It’s unclear to me if he’s still talking about GCMs or models in general? We may agree there is a bias towards one equilibrium or the current equilibrium. In some ways that’s preferable to an unpredicted state.

“Computer models have such a strong tendency to fall into the White Earth equilibrium that climatologists find themselves wondering why it has never come about. It may simply be a matter of chance.”

It’s my understanding that the White Earth is colder than the recent glacial periods. If it’s true that they try at all costs to avoid this, why do the models go there?

“Yet it takes no great imagination for a climatologist to see that almost-intransitivity might well explain why the earth’s climate has drifted in and out of long Ice Ages at mysterious, irregular intervals. If so, no physical cause need be found for the timing. The Ice Ages may simply be a byproduct of chaos.”

And I would take the long time scales of ice ages and shorten them all the way down to decades and shorter time spans. I like the idea of understanding the glacial interglacial cycle to find the same processes that governs the time spans we worry about.

“The system is not in equilibrium, never was and will never be. It is even its defining feature. It can’t “return” to some equilibrium it has never been in to begin with. I thought at least this basic truth would be known.” – Tomas Milanovic

“…components in the system are inherently chaotic; there are feedbacks that could potentially switch sign, and there are central processes that affect the system in a complicated, non-linear manner. These complex, chaotic, non-linear dynamics are an inherent aspect of the climate system.” – IPCC 14.2.2

I finding it difficult to accept the idea of a climate equilibrium. I do agree that that point of view will often work (the shorter the time span the better), and is more tractable than multiple climate states. Equilibrium states solve all kinds of engineering problems, are practical and economical. But perhaps at the tails of a probability distribution function, we find other states.

More complete quote:

“Climatologists who use global computer models to simulate the long-term behavior of the earth’s atmosphere and oceans have known for several years that their models allow at least one dramatically different equilibrium. During the entire geological past, this alternative climate has never existed, but it could be an equally valid solution to the system of equations governing the earth. It is what some climatologists call the White Earth climate: an earth whose continents are covered by snow and whose oceans are covered by ice. A glaciated earth would reflect seventy percent of the incoming solar radiation and so would stay extremely cold. The lowest layer of the atmosphere, the troposphere, would be much thinner. The storms that would blow across the frozen surface would be much smaller than the storms we know. In general, the climate would be less hospitable to life as we know it. Computer models have such a strong tendency to fall into the White Earth equilibrium that climatologists find themselves wondering why it has never come about. It may simply be a matter of chance.”

“To push the earth’s climate into the glaciated state would require a huge kick from some external source. But Lorenz described yet another plausible kind of behavior called “almost-intransitivity.” An almost-intransitive system displays one sort of average behavior for a very long time, fluctuating within certain bounds. Then, for no reason whatsoever, it shifts into a different sort of behavior, still fluctuating but producing a different average. The people who design computer models are aware of Lorenz’s discovery, but they try at all costs to avoid almost-intransitivity. It is too unpredictable. Their natural bias is to make models with a strong tendency to return to the equilibrium we measure every day on the real planet. Then, to explain large changes in climate, they look for external causes—changes in the earth’s orbit around the sun, for example. Yet it takes no great imagination for a climatologist to see that almost-intransitivity might well explain why the earth’s climate has drifted in and out of long Ice Ages at mysterious, irregular intervals. If so, no physical cause need be found for the timing. The Ice Ages may simply be a byproduct of chaos.”

Chaos: Making a New Science, James Gleick

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