More Than Moonglow
Between El Nino and conferences on global warming, weather, climate, and the disagreements among scientists about weather and climate have been filling the news lately. Given the complexity of this dynamic planet, it would be astounding if researchers didn't disagree. To me, the really amazing thing is that scientists are doing so well at making increasingly precise measurements and then building them into ever more accurate projections. The improving precision is well illustrated by the significantly larger quantity recently assigned to the amount by which the full moon heats the polar atmosphere.
Almost sneaked that one past you, didn't I? Yes, the moon apparently does affect temperature at high latitude--though not so much that you should run out and moonbathe in the buff this weekend. Near the time of the full moon, the polar air is warmed by a bit more than half a degree centigrade over its temperature at the time of the new moon. That may not sound like much, but it's about a quarter of the upward change predicted by some mathematical models for the polar regions over the next several decades.
The experts apparently have long accepted some lunar warming effect, which was news to me, but previous measurements showed the full moon adding only about two hundredths of a centigrade degree to the polar atmosphere's temperature. The most recent study, performed by scientists at Arizona State University in Tempe (where, perhaps, people have more obvious reason to worry about additional heat than they do in Alaska), analyzed satellite-gathered data from about 200 lunar cycles. As well as refining the numbers, the work showed that the full moon had virtually no effect on temperatures in the tropics and only a slight effect on temperatures in the temperate zone. But poleward of the 70th parallel in both northern and southern hemispheres, the effect was 25 times greater than it was closer to the equator.
John Shaffer, a member of the Arizona research team reporting the polar heating effect, admits that it's barely possible that radiation from the moon might be putting glitches in the satellite instrumentation, but the odds are much better that the high-latitude warming is a real effect.
Now, I admit that when I read the report and interview with Shaffer in a recent issue of the journal New Scientist, I quickly jumped to the conclusion that lunar radiation would be the heat source. Sure, I knew that the moon shines by reflecting sunlight; it doesn't generate light (and heat) on its own as the sun does. But I've propped sheets of metal behind campfires to reflect radiant energy back toward chilly campers, and it works. I could extrapolate from campfire to sun, metal sheet to moon, and come up with a reasonable-sounding explanation for the additional warmth.
But, like a lot of my other reasonable-sounding explanations, it's wrong. Shaffer and his colleagues think the cause is heat transfer within the earth's atmosphere. They suspect that tidal pull from the full moon changes major wind patterns in the upper atmosphere--perhaps affecting the jet streams so loved by TV meteorologists, as they show these rivers of air snaking above the world from west to east, nudging high- and low-pressure systems around continental features, fencing warm air masses away from colder ones. The Arizonans are presently guessing that the moon's gravitational tug alters waves within the wind systems, somehow either enhancing or suppressing their usual effects. But, whatever the exact mechanism, the researchers are pretty sure that the polar air mass is warmer under the full moon because somehow more equatorial warmth gets carried to the ends of the earth.
Nobody's yet speculating on what this detail may mean to the overall problem of global warming, but it may alter a few northerners' perceptions. Consider: if you're in Barrow and hear sled dogs sing to the full moon, maybe they're just complaining because they're hot.
