Climatic seeds planted in September blossom into a fascinating pattern by December
When the next round of monthly updates on global temperature trends comes out, my guess is that the record or near-record warmth of 2010 recorded through the end of November will be tempered a bit by cooling in December.
That’s what the maps above suggest to my eye. Produced by Remote Sensing Systems, they show how global temperatures near the surface, as determined by satellite, varied from the 1979-1998 average. September’s anomalies are on the left; December’s on the right. Anomalously warm areas are depicted in appropriately warm colors, and visa versa.
But I’m struck even more by the pattern of warm and cold, which may well be more significant.
Take a look at the reddish warm areas during September over northeastern Canada and Greenland, western Russia extending down below the Caspian Sea, and far northeastern Asia. Now, look what happened in December. The warmth in these areas greatly intensified and became more clearly defined by the end of the year. These are now true hot spots.
But that clear delineation seems to have occurred because the warm areas became enveloped by anomalous cold. Areas that were cool in September, including central Europe and Siberia, got significantly colder still, and the cool spot over central Europe expanded. Meanwhile, a new one spread over the eastern U.S.
So in a sense, warm and cold spots in September were like seeds that blossomed during autumn into a striking and highly contrasting pattern by the end of December.
But that metaphor is not entirely accurate. That’s because the pattern of anomalous warmth evident can be traced farther back than September. (Remember the devastating Russian heat wave last summer?) Play with the interactive monthly anomaly maps from RSS to check it out for yourself.
A similar fascinating pattern is revealed by anomaly maps from NOAA’s Earth Systems Research Laboratory:
The ESRL analysis of surface temperature anomalies is based on data from a variety of sources, including satellites and surface temperature monitors, along with computer modeling. (To create your own graphics using ESRL data — and not just for temperature but for a variety of other factors, such as winds, humidity, soil temperature and host of others — go here.)
What’s going on?
The cooling evident in the eastern Pacific in September and December is clearly due to La Niña conditions. But there is quite a bit more going on climatically.
The Arctic Oscillation (also called the “Northern Annular Mode,” or “NAM”) was in a deeply negative phase through most of December and half of November — as it was for parts of last winter too. When this is the case, the odds are that much of the United States east of the Rocky Mountains will be cooler than normal, whereas Greenland and northeastern Canada will be warmer. That seems consistent with what these maps reveal.
But how do La Niña, the Arctic Oscillation and other climatic phenomena interact to influence weather patterns? I’m not sure that scientists have a full and satisfying answer to that questions.
Anyone care to weight in on this? Please leave a comment!
Moreover, why has the Arctic Oscillation been stuck in such a negative phase for two winters now?
According to one theory, declines in Arctic sea ice change atmospheric circulation patterns in ways that tend to pour unusually cold and snowy weather toward the south but also leave large parts of the Arctic warmer than usual. (Climate Central has a clear and concise explanation here.)
Another theory, the one advocated by Judah Cohen in the New York Times just prior to the Christmas blizzard in the Northeast (great timing!), also invokes declines in Arctic sea ice. But in a somewhat different way.
According to Cohen, these declines allow more water vapor to build up in the atmosphere in the north, leading to snowier autumns in Siberia. This more extensive snow cover reflects more of the Sun’s rays back into space, thereby altering atmospheric circulation in just the right way to create the pattern of warming and cooling that has been observed.
Which is right? Perhaps some combination of the two? Perhaps neither? How might these phenomena interact with La Niña and other climatic phenomena? And where does the long-term global warming trend fit in?
Once again, the climate system is fascinating in its complexity — with much still to be learned by climate scientists.
When the actual climate reports for December are published, it will be interesting to see whether I’m eyeballing these anomaly maps correctly. Will the reports show an overall easing of unusually warm conditions at the end of 2010? If so, expect to hear the usual claims that global warming has stopped, that we’re on the verge of a new Ice Age, and God only knows what else.
If anyone you know makes that argument, refer them to the graphic below from Remote Sensing Systems. It shows the long-term trend of near-surface temperatures, as determined by satellite measurements:
In the latter part of 2010 (at the extreme right of the time series) you can make out a decrease in the intensity of the global temperature anomaly. But look at that 0.0 marker. Anything above it signifies temperatures that were anomalously warm compared to the long-term average. And at the end of December, the global average temperature was still considerably above that 0.0 mark.
The graph also shows lots of ups and downs — an erratic sawtooth pattern. Despite this, the long-term trend couldn’t be clearer: an overall warming since satellite monitoring of surface temperatures began in the late 1970s.
Every other major analysis of global temperatures reveals the same thing: a clear warming trend over the course of the past few decades. And it will take much more than one month of cooling to reverse that.
Lastly, it will be interesting to see how the temperature anomalies in December affect the final ranking for 2010. Will the year go down in the record books as the warmest since record keeping began in the late 1800s? Or will cooling in December prevent that distinction?
We’ll probably know by the second week of January when the first global temperature reports come in.