Cross-posted from NextGen Journal
“That’s some global warming”, Fox News proudly announced. “Rare winter storm dumps several inches of snow across South.” It’s cold outside, and/or it’s snowing, so therefore global warming can’t be happening. Impeccable logic, or rampant misconception?
It happened last winter, and again so far this season: unusual snow and extreme cold thrashed the United States, Europe, and Russia. Climate change deniers, with a response as predictable as Newton’s Laws, trumpeted the conditions as undeniable proof that the world simply could not be warming. Even average people, understandably confused by conflicting media reports, started to wonder if global warming was really such a watertight theory.
But sit and think about it for a minute. If it’s cold right now in the place where you live, that doesn’t mean it’s cold everywhere else. It’s simply not possible to look at your little corner of the world and extrapolate those conditions to the entire planet. There’s a reason it’s called global warming, and not “everywhere-all-the-time warming”. Climate change increases the amount of thermal energy on our planet, but that doesn’t mean the extra energy will be distributed equally.
That said, an interesting weather condition has been prominent over the past month, telling a fascinating story that begins in the Arctic. At the recent American Geophysical Union conference in San Fransisco, the largest annual gathering of geoscientists in the world, NOAA scientist Jim Overland described the situation.
Usually in winter, the air masses above the Arctic have low pressure, and the entire area is surrounded by a circular vortex of wind currents, keeping the frigid polar air contained. Everything is what you’d expect: a cold Arctic and mild continents. These conditions are known as the positive phase of the North Atlantic Oscillation (NAO), an index of fluctuating wind and temperature patterns that impacts weather on both sides of the Atlantic.
The negative phase is different, and quite rare: high pressure over the Arctic forces the cold air to spill out over North America and Eurasia, allowing warm air to rush in to the polar region. Meteorologist Jeff Masters has a great analogy for a negative NAO: it’s “kind of like leaving the refrigerator door ajar–the refrigerator warms up, but all of the cold air spills out into the house.” The Arctic becomes unusually warm, and the temperate regions of the surrounding continents become unusually cold. Nobody visually depicts this pattern better than freelance journalist Peter Sinclair:
So what’s been causing this rare shift to the negative NAO the past two winters? In fact, global warming itself could easily be the culprit. Strong warming over the Arctic is melting the sea ice, not just in the summer, but year-round. Open water in the Arctic Ocean during the winter allows heat to flow from the ocean to the atmosphere, creating the high pressure needed for a negative NAO to materialize. Paradoxically, the cold, snowy weather many of us are experiencing could be the result of a warming planet.
An emerging debate among scientists questions which force will win out over winters in Europe and North America: the cooling influence of more negative NAO conditions, or the warming influence of climate change itself? A recent study in the Journal of Geophysical Research predicts a threefold increase in the likelihood of cold winters over “large areas including Europe” as global warming develops. On the other hand, scientists at GISS, the climate change team at NASA, counter that extreme lows in sea ice over the past decade have not always led to cold winters in Europe, as 7 out the past 10 winters there have been warmer than average.
Amid this new frontier in climate science, one thing is virtually certain: global warming has not stopped, despite what Fox News tells you. In fact, despite localized record cold, 2010 is expected to be either the warmest year on record or tied for first with 2005 (final analysis is not yet complete). What you see in your backyard isn’t always a representative sample.
ClimateSight 
Excellent overview. I did the first interview with Overland last summer on this topic at the Polar Science conference in Oslo. There were other researchers there who showed similar results notably Meiji Honda, a senior scientist with the Climate Diagnosis Group at Japan’s Agency for Marine-Earth Science and Technology.
http://stephenleahy.net/2010/09/13/arctic-melt-down-is-bringing-harder-winters-and-permanently-altering-weather-patterns/
Thanks for that link, Stephen. It’s awesome that you got to cover IPY – I heard it was a really good conference. -Kate
There once was a little child,
Who thought his backyard was the whole world.
If it was raining in his backyard,
Then surely, it must be raining at the South Pole.
If it was snowing in his backyard,
Then it was obviously snowing in a place called Brazil.
Then that little child ‘grew up’.
Yet he still lived in his backyard.
Only difference was that his backyard had gotten bigger.
It had become the whole United States.
So when it was snowing in the United States,
Well, what did the rest of the world matter?
“A recent study in the Journal of Geophysical Research predicts a threefold increase in the likelihood of cold winters over “large areas including Europe” as global warming develops…..
.. On the other hand, scientists at GISS, the climate change team at NASA, counter that extreme lows in sea ice over the past decade have not always led to cold winters in Europe, as 7 out the past 10 winters there have been warmer than average.”
So basically regardless of what happens in the future it will have been predicted and explained by global warming. Just point to one of the two studies and don’t mention the other. Then say “Yup, we knew it all along”.
Not every set of observational data would confirm a warming planet. There are many major indicators of global warming that are clearly predicted to go in a certain direction – for example, the temperature of the planet as a whole, or the sea ice cover in the Arctic. The climate system is so nuanced, though, that some regional and seasonal effects could go either way, such as winter temperatures in regions influenced by circumpolar currents.
Assuming that scientists would cover up past uncertainty in these situations, once they understand what’s going on, is at best naive, and at worst libelous. For every instance of minor scientific uncertainty, how can you accuse them of conspiracy in the future, when the future hasn’t even happened yet? -Kate
See Figure 1.
If you tried to embed something here, Brian, WordPress stripped it out…send me an email or a comment with the link and I’ll embed the image for you. -Kate
The red is the blue curve shifted to a higher mean temperature, i.e. through global warming (that’s all the term means: An increase in mean global temperature). The X axis is simply temperature.
Probability density is a funky term, but in essence, the area under the curve corresponds to probability. The area under the entire curve is 1.00, since the probability of *something* happening is 1.
If you want to know how likely something this extreme or more extreme is, draw a line at some threshold; the area under the part of the curve it cuts off is the corresponding probability.
Here, if you want to know the probability of a given temperature or higher, you draw the line marked Threshold at the given temperature. The area under the curve to the right of that line is the probability of temperatures that extreme or higher.
Under the “warming world” red curve, the probability of an extreme event goes up from the older world blue curve. The probability of “VERY” extreme events, formerly so low as to be not considered, also goes up (that’s the part of the red curve that is not also under the blue curve; one example would be the Moscow heat wave).
However, as the temperature goes up, there is *STILL* a portion of the curve over the low-temperature. They just become less likely – they don’t disappear altogether, except at the tail end of the curve (the area on the blue curve that isn’t also under the red curve).
This is very simplistic – for instance, it assumes the shape of the curve doesn’t change as mean temperature rises – but it should get the point across. Global warming – an increase in mean global temperature – does NOT mean no more winters.
This is also just on a more general point than the specific NAO influence – that’s more about ocean currents, which is a rather complex field (did you read the paper at all? If you did, could you follow their methods and discussion?). But it serves to counter the general denialist problem of thinking that the word “warming” precludes any cold at all.
It was an adaptation of this figure from the IPCC TAR:
It doesn’t exactly counter Alen’s claim, but it does target a common, underlying sentiment shared by people who make that sort of argument. People don’t seem to comprehend the idea of a probability distribution (or really any distribution, in the statistical sense). It seems to be a blind spot in our reasoning, similar to the exponential function.