Spring is cancelled

To say that an unusually cool summer debunks climate change is like saying that a cold patch in late April (or September in the Southern Hemisphere)  means that Spring is cancelled.

Or as Bill Maher puts it:

One major reason [people don't believe in climate change] ...  is that we had a very long snowy winter, which is the same as saying the sun is not real, because last night it got dark.

Mike Haseler fell for this error on his Scottish Sceptic blog.

Open the fridge door

How does a warming Arctic cause winter cold in Europe and Northern America? Or, in other words, if the globe is warming, why the cold freeze?

It's because the Arctic refrigerator door has been opened and the cold air spilled out at the bottom, according to John Cook of Skeptical Science.

The refrigerator door is the jet stream that marks the differences in atmospheric pressure in higher latitudes (20N) compared with mid-latitudes (37-45N). This difference in pressure is measured by the Arctic oscillation (AO)  index or Northern Annular Mode/Northern Hemisphere Annular Mode (NAM).

NASA climatologist Dr. James E. Hansen explains the mechanism by which the AO affects weather at points far from the Arctic:

The degree to which Arctic air penetrates into middle latitudes is related to the AO index, which is defined by surface atmospheric pressure patterns. When the AO index is positive, surface pressure is low in the polar region. This helps the middle latitude jet stream to blow strongly and consistently from west to east, thus keeping cold Arctic air locked in the polar region. When the AO index is negative, there tends to be high pressure in the polar region, weaker zonal winds, and greater movement of frigid polar air into middle latitudes.

So warmer temperatures in the Arctic mess with the air pressure and this tends to make the refrigerator door swing open. Sometimes it just chinks open a little bit, other times it's like a teenager came to raid the fridge. That's when Europe really freezes!

Boxing kangaroo

Here's the professor training his boxing kangaroo called Weather.

The way I like to think about it is to think of weather as a boxer throwing punches at us. Over history, weather has always thrown these punches at us – in Brisbane we had floods in 1974, and in the late 1800s we had floods that went through Brisbane as well. So there’s always been these punches coming at us, but what we’re doing now with global warming is like training the boxer to throw harder and faster punches at us.

John Cook, Skeptical Science

You could say we're not just training Weather, we are also giving him a different feedmix – one with more carbon dioxide, methane, nitrous oxide, and ozone.

Boxing a glacier

Here is Stephen Colbert talking about Jesse Jackson.

You can ask him anything, but he's going to say what he wants at the pace that he wants. It's like boxing a glacier. Enjoy that metaphor, because your grandchildren will have no idea what a glacier is.

White House Correspondents' Dinner, April 29, 2006

Climate change is a lot like Jesse Jackson. You can say what you want, but it keeps happening at the pace it wants.

Mother Nature is just chemistry, biology and physics. That's all she is. You cannot sweet-talk her. You cannot spin her. You cannot tell her that the oil companies say climate change is a hoax. No, Mother Nature is going to do whatever chemistry, biology and physics dictate. Mother Nature always bats last, and she always bats 1.000.

Robert K Watson

Oh, and the glaciers keep retreating. The National Snow and Ice Data Centre says that "Since the early twentieth century, with few exceptions, glaciers around the world have been retreating at unprecedented rates."

Loaded dice

How do we know whether today's weather event is caused by climate change? While we can't yet link specific events to climate change, scientists can look at patterns of extreme weather and ask whether the likelihood of these events was heightened by human-driven climate change.

Think of a pair of dice that you throw every day. Rolling a pair of sixes happens now and then. But rolling five in a row looks suspicious.  Human-induced climate change has loaded the dice toward certain extreme events.

In their paper, Public Perception of Climate Change and the New Climate Dice, James Hansen, Makiko Sato, Reto Ruedy find that 

Hot extremes, which covered much less than 1% of Earth's surface in the period of climatology, now typically cover about 10% of the land area. It follows that we can state, with a high degree of confidence, that extreme anomalies such as those in Texas and Oklahoma in 2011 and Moscow in 2010 were a consequence of global warming, because their likelihood in the absence of global warming was exceedingly small.

Proceedings of the National Academy of Sciences, April 2012

The loaded dice analogy was used by Dim Coumou, a climate scientist at the Potsdam Institute for Climate Impact Research in Germany in this Washington Post article on 29 March 2012.

Climate Bites has a good post on dice. They note that climate change has put an extra six on the dice (e.g. the five  got an extra dot). When you roll the dice now you are twice as likely to throw a six, and you never know whether this particular six is the ordinary, by chance, six, or whether it is the new climate change six.

Joe Romm used the loaded dice analogy in this article about  the unprecedented March (2012) heat wave that was “unmatched in recorded history” for the U.S. (and Canada).  New heat records swamped cold records by the stunning ratio of 35.3 to 1.