Thursday, April 17, 2008

Cycles of climate: Variations

If infrared-active gases were causing significant "global warming" as popularly conceived, what effect would it have on climate cycles? The general effect would follow what an earlier posting pointed out: an easing of relative differences. Temperatures would rise everywhere and everywhen. Cycles would remain but become less pronounced in intensity overall. Shorter cycles, like El NiƱo (ENSO), would be damped down relatively more; while longer ones, like the Pacific (Multi)Decadal Oscillation, would be damped down relatively less, assuming that the "global warming" is gradual. But all would be damped.

The main heat reservoir of climate cycles is the oceans. Their temperatures would also rise, although much more slowly than the atmosphere. Just for that reason, we should expect fewer tropical storms and a decline of "horizontal" weather generally.

Being versus becoming. A more exact statement about tropical storms and "horizontal" weather generally: we expect these to become more important, not during cool periods, but cooling periods. That's when different heat reservoirs in the climate system (oceans and atmosphere in particular) face larger temperature differences: the air cools off faster than the water, for example, making hurricanes easier to make. But once the cooling stops, and it's just cooler, this enhancement of extreme weather should fade. That is apparently what happened in 1999-2005: cooling first, now it's just cooler than before, with the rate of change slowed or stopped.

Why isn't there a symmetry going the other way? For example, if it's not warmer, but warming, the air heats up faster than the ocean. But that's just the point. The ocean will lag, and not have the excess heat to drive tropical storms so much. Over land, the situation is reversed: the land warms up faster than the air. So we probably should expect more overall mid-continent thunderstorm activity, but locally formed and dissipated - not associated with horizontally moving fronts.

A final thought on climate cycles. A few postings ago, I mentioned that tests of statistical significance (using modern non-parametric methods) suggest 50-80% of temperature trends in modern times are connected to solar variability. Meanwhile, the global sync'ing of regional climate oscillations has its own powerful effect, one that seems to be off the same level of significance. It's probable that most of the known climate variability on times scales shorter than the Ice Ages (less than roughly 10,000 years) is due to a mix of these two factors.

Again, a very important topic, not given enough attention, multidisciplanarily marginal in the academy, and subject to a strong tendency to shove down the memory hole.

POSTSCRIPT: We'll know this "global warming crisis" is serious when the people who keep claiming it's a crisis start acting that way.

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