Jim Hansen suggests an explanation here. "If It's That Warm, How Come It's So Darned Cold?," an essay on regional cold anomalies within near-record global temperature, by J. Hansen, R. Ruedy, M. Sato, and K. Lo, is at the Columbia U site. Hansen says (p. 13),
Weather fluctuations exceed the magnitude of average global warming over the past half century. However, the perceptive person should be able to notice that climate is warming on decadal time scales. The global temperature trend over the past few decades has been strong enough that there is a noticeable 'loading' of the climate dice that define the probability of unusually warm or cool seasons.The weather fluctuations Hansen speaks of are put into perspective by what The Economist 1/16-22/10 p. 20 calls Arctic Roll:
The Earth is in a negative phase of the Arctic oscillation, a particular mode of atmospheric circulation, which explains the unusually cold winter that is chilling America and northern Europe. But what intrigues climatologists is the uncertainty over whether this phase will ultimately cause Arctic sea ice to thicken or melt.Read more here; the full text, "Oscilloscope," is at the journal's greenview blog, posted 1/11. An update, here, is Dry Cold 2/1. That post tries to make sense of the news that stratospheric water vapor is diminishing, which may put a brake on global warming. See Susan Solomon et al., "Contributions of Stratospheric Water Vapor to Decadal Changes in the Rate of Global Warming," Science online Jan 28. WSJ's reaction 1/29, "Slowdown in Warming Tied to Water Vapor," is here. And here's NYT's. But RealClimate has doubts:
If the lower stratosperic water vapor (LSWV) is relaxing back to some norm after the 1997/1998 El Nino, then what we are seeing would be internal variability in the system which might have some implications for feedbacks to increasing GHGs [greenhouse gases], and my estimate [sez Gavin Schmidt @ NASA/Goddard] of that would be that this would be an amplifying feedback (warmer SSTs [sea surface temps] leading to more LSWV). If we are seeing changes to the tropopause temperatures as an indirect impact from increased Asian aerosol emissions or solar-driven ozone changes, then this might be better thought of as impacting the efficacy of those forcings rather than implying some sensitivity change.An amplifying feedback of warmer seas leads to less high-altitude vapor, an internal variability of El Nino pulses. The details are here. In short: if you think that global warming slows down, dream on. Climate is a frame of long-term waves. In an interview with Der Spiegel, Dirk Notz @ Max-Planck Institut fuer Meteorologie explains,
Unfortunately there is a public impression that climate change would mean that from now on we are going to see new temperature records every year. That's not the case. What we can say, with very high probability, is that the climate, on average, is warming up, whereby for us "climate" means thirty-year weather averages.See it here. I like to think of climate change as the injection of net energy into the Earth System. Global warming is one side of the climate coin. The other I'd call Planetary Powering-Up -- due to the new systems energy, seasonal swings increase; the wave amplitude or vertical distance between peaks and troughs grows. That's why it's so cold. Just like it already was last winter in Europe.
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.
Eighty-two months left.