Sometime this month, I'd like to review the emerging consensus on Copenhagen. Right now, though, I wonder more about climate than about policy. Why is it so chilly? I was freezing in Munich three weeks ago; I was freezing in Osaka two weeks ago; I'm freezing in Tampa now. The citrus harvest is shot. The banana trees are dead. The palms are frost-bitten. What's happening to global warming? Philosophers like me, who are grappling with the new reality, are confused. Can climatologists help with the meaning of all this?
Jim Hansen suggests an explanation here. He says (p. 13),
Weather fluctuations exceed the magnitude of average global warming over the past half century.The fluctuations are called by The Economist 1/16-22/10 p. 20 Arctic Roll. The journal's greenview blog, post 1/11, has this:
The Earth is in a negative phase of the Arctic oscillation ... which explains the unusually cold winter that is chilling America and northern Europe.Arctic Roll (or Arctic Oscillation) is a wave of alternating pressures up north. The wave is big, affecting everything from the 20th degree latitude N upwards (think of Cuba and the Virgin Islands as the southern edge of the Roll). The wave is slow, going up and down once a generation; each phase lasts forty years. It alternates air pressure at sea level at the North Pole, twisting up- and downswings at the pole and elsewhere in the Northern Hemisphere.
Here is how this works. Consider the causal web of the Earth System before climate change. During winters colder than usual in the US and in Europe (for Japan, we need El Nino; different story), it's warmer than normal in the Arctic. It's still stupefyingly cold up there: it's the North Pole, winter, and the Arctic night. Still, at other such times, it can be even colder. In that sense it's warmer than normal. This warmer polar air is at higher pressure. The high pressure patch patch at the pole is a backed-up drain pushing air away from the center. The winds, constant westerlies, are pushed sideways by the polar overflow. Loaded up with polar air, the west-east winds now spiral out and away down south. The air in the mid-latitudes of the Northern hemisphere gets colder and lower in pressure. A temporary balance: high-pressure arctic overflow and low-pressure mid-latitude suction keeps cold air rolling south. That's the negative phase.
During the positive phase, winters are warmer than normal in the US and in Germany, and it's colder than normal in the Arctic. The cold air is at low pressure. The patch of low pressure over the pole is like a vortex that swirls westerlies around its center. They carry cold air around and around. This merry-go-round keeps the cold circling the Pole; the Arctic cold doesn't spread southwards. The low pressure over the pole is also held in check, or reversely mirrored, by a high pressure zone over the mid-Atlantic. So when the oscillation lowers Arctic pressure, it raises pressure in the middle latitudes, and it's warm where we are. But, not now, since the positive phase is over. Here's info from Washington U and from BBC's earth watch blog.
The Arctic Roll went up in the first forty years of the past century, then went down until the nineteen eighties, and now is up again, presumably for another ten years or so. This is how it's always been. So, basically, in the temperate latitudes of the northern hemisphere, we've entered a periodic, regular, and multi-decadal cold phase, after having spent the past forty years in a periodic, regular, and multi-decadal warm phase, all thanks to the Arctic Oscillation.
Hansen suggests that these cycles can obscure the overall warming trend, but in a way the trends also enhance the cycles. This is not a philosopher contradicting a climatologist (a losing proposition), but rather a reminder of the basics vis-a-vis highly specialized readings. And the basics are that global warming entails snowmageddon.
Essentially climate change is the injection of net energy into the Earth System. Global warming is one side of the climate coin. Call the other the Power-Up -- due to the new systems energy, seasonal swings increase. Look at the graph from Washington U. The Power-up translates into blistering summers and freezing winters. Q.E.D.
Fascinating, from the perspective of civil evolution, is that the temporary cooling tempts policy makers and the public to dismiss the menace of climate change and opt for a laissez-faire attitude. The negative phase of the Arctic Roll means global warming won't go up much in the next few years. But the first feedback loops (methane bubbling, ice melt) have come online. And the first cascading effects (dried-out lands, sour seas) have started up. And year after year, atmospheric CO2 concentrations are increasing, and anthropogenic systems pressures keep mounting. This negative phase of the Arctic Roll hides their effects. That's double trouble. One, because plainly evident effects would be cognitively helpful; they would help people wise up. Two, because when the Arctic Roll turns positive, the Earth System will have more power available for the upswing and react harshly. It's the setup for a blistering orb. Creepy about the Arctic Roll is that old harbingers and new modeling may well be all the warning we'll get before the runaway. This twist of events makes climate change into an IQ test for the species.
PS: For Solomon's much-discussed paper and its Dry Cold explanation, possibly a red herring, I defer to the realclimate review.
Eighty-two months left.