This was written by Rebecca Anderson on May 10, 2010.

A month or so ago, I wrote about how big snowstorms and climate change – how these snowstorms don’t actually mean climate change isn’t happening and how the snowstorms themselves might actually have been caused by climate change.

From Feb. 11, 2010 – such a cool image!

It turns out that I wasn’t the only one wondering if these storms were caused by climate change.  A lot of other people were, too, and one group at NOAA who calls themselves CSI (that’s Climate Scene Investigators – cute, eh?) actually had the tools and the smarts to find out.

The first thing they discovered, by looking at temperatures along the East Coast this winter was that they were exceptionally COLD.  It was actually the 18th coldest winter for the U.S. since 1895.  (Although globally, this winter was the 5th warmest ever recorded.  Go figure.  This is why we talk about global warming.)  So that puts a big hole in the theory right from the start – if climate change was causing bigger snowstorms by warmer air holding more moisture, there would actually have to be warmer air.  And there wasn’t.

The CSI team also didn’t find any evidence of a trend of increasing snowfall over time, as the planet has warmed up.  Not looking good for the climate-change-causing-big-snowstorms theory.  Here’s what they think DID cause the record-setting snow:

1.    El Niño

Seems like El Niño can be blamed for just about anything.  Missed a deadline?  El Niño.  Late for work?  El Niño.  Caught for speeding?  El Niño.  I see lots of potential here for a universal scapegoat.

Here’s what he did this time:

El Niño tends to shift the track of storms across the U.S. towards the south (which also explains why it was so dry in B.C. for the Olympics).  Besides this, El Niño also provides 1 of 2 essential components for a blizzard:  Lots of moisture.  Special delivery from the extra-warm Pacific Ocean.
(Check out this really cool graphic of El Niño bringing moisture across the southern U.S.  It takes a while to load, but it’s worth it.)

But besides moisture, the other missing ingredient is temperatures cold enough to snow.  This is where the second player comes in:

2.    Arctic Oscillation

This is where it gets cool (okay, literally).  The Arctic Oscillation has to do with differences in air pressure around the Arctic.  When it’s in its positive phase, there’s low pressure over the Arctic and high pressure surrounding the Arctic, which means that cold air stays up by the North Pole.  In the negative phase, however, it’s the opposite: high pressure over the Arctic and lower pressure surrounding it.  This funnels cold air down from the Arctic into North America, Europe and Asia and explains why it was so cold this winter throughout all of these regions.

So the combination of cold air coming down from the Arctic, combined with lots of moisture coming across the southern U.S. from El Niño created literally the perfect storm: Snowpocalypse, Snowmaggedon or whatever you want to call it.

The interesting thing is that this was happening amidst an exceptionally warm winter globally – 2009 was the 2nd warmest year on record (tied with 5 others in the last 12 years), according to GISS, and 2010 looks like it might be shaping up to break all records and be the warmest year ever recorded.  (Read here)

So how do the two fit together?  Hard to say.  We’re projected to have more El Niños in the future, although it’s still tough to say whether that trend is here already or not.  But the trend for the Arctic Oscillation is actually towards more positive phases (not negative like this year) – this has been documented already since 1950 and is projected to continue to be more positive in the future.  So exactly what set up this winter’s negative one is unclear.

I’ll steal an analogy for how to look at this from the original NOAA article:  Compare climate and weather to a game of pinball.  Each time you flick the ball, you don’t know exactly where it’s going to end up.  This is like the variability in weather.  But in general, you know that the ball will often end up in certain pockets or pathways a certain percent of the time.  This is akin to climate.  And climate change is what happens when you put one side of the pinball machine up on a block and tilt it – you make it way more likely that the ball will follow a certain set of pathways than before – even if it doesn’t happen every single time.

Maybe not the best analogy ever, but I couldn’t resist the pinball reference.

To read the full articles about this from NOAA’s new climate.gov website, see below.  These articles are really well-written and intended for a general audience – highly recommended!

http://www.climatewatch.noaa.gov/2010/articles/can-record-snowstorms-global-warming-coexisthttp://www.climatewatch.noaa.gov/2010/articles/forensic-meteorology-solves-the-mystery-of-record-snows