Part of this post appeared on the original blog under the name “A Natural Complexity” in 2012.
A new El Niño is beginning, apparently.
El Niño refers to an unusual weakening of the trade winds, which causes warming of certain parts of the Pacific ocean. The name means “the Child,” referring to the Christ Child, because of the bad fishing the warm water causes off of Peru around Christmas during El Niño years. The pattern radically changes the weather across much of the globe. For example, El Niños partially suppress Atlantic hurricane activity but increase hurricane formation in the Pacific. A stronger trade winds and a cooling of the Pacific is called La Niña (“the Girl,” because it is the opposite of “the Boy”) and likewise alters worldwide weather. The Pacific moves between these two extremes every three to seven years for reasons no one really knows. The cycle is called ENSO, for El Niño Southern Oscillation.
Earlier this month, NOAA (National Oceanic and Atmospheric Administration) announced that while the ENSO is currently still neutral, the Pacific is warming in ways that suggest an El Niñowill develop sometime this year. When it will develop or how severe it will be if it does, they cannot say yet. NOAA reassesses the ENSO every month, and they should be much more sure of their prediction in June.
ENSO extremes cause extreme weather of various types, so if an El Niño does develop, we can expect this coming winter to bring unseasonably warm weather to parts of Alaska and Canada and a lot of snow and rain to the Southeastern United States. Some Americans will therefore announce that global warming is definitely happening because of all the weird weather, others will announce that global warming can’t be happening because look at all this snow, while still others will insist that it is just El Niño, which has recurred for thousands of years and has nothing to do with greenhouse gases. Little sub-arguments will rage over whether and how global warming and the ENSO interact (nobody actually knows). The great debate will rage; is this weather natural?
And that is the wrong question.
The truth is that global weather patterns are extremely complicated and any particular weather event has many different causes, all operating together. Identifying what caused any particular hot day is a bit like attributing a wave in a crowded swimming pool to one particular swimming kid. The occasional cannon ball leap aside, the question cannot be answered. Scientists don’t try.
What scientists do instead is to look at probabilities. They look at the swimming pool and they measure the waves and they analyze the measurements with powerful computers. They ask “is this group of waves about what we would expect, given that a dozen kids are hopping up and down in the water?” If the answer is no, they don’t need to know which wave is natural and which wave isn’t; they know the pattern as a whole has changed and there is something new happening in the water.
When climate scientists announced that the heat waves and droughts of 2012 were definitely the result of global warming, they did not mean that natural weather has ended, or that we will never have an unseasonably cold spell again (we’ve have some since then). What the scientists meant was that the pattern has changed. There is an extra kid in the pool, now. And every wave, big and small, will now be the combined result of all the original kids plus the new one.
This winter, we’re going to be swimming around next to a very bouncy kid, the Boy, El Niño. He’s been in the pool a long time. He’s one of the older kids, though he isn’t always splashing around so much. But even though the Boy might be drawing attention to himself, each wave will still be the result of many causes all interacting together, and the new global warming kid will still be in the pool, making the entire pool different than it would be if he were not there.
The new kid in the old pool is us.