Did Global Warming Cause All This Weird Weather?

Over the last few months, severe weather events around the world have been headlines in the news. Huge winter snowstorm blankets the Midwest just this week, with over 2 feet of snow in much of the country. The east coast of the US has been hit with several snowstorms of significant depths this winter already. Europe, including normally mild England, has been hit with huge snowstorms that brought air travel to a halt for days. Meanwhile in the southern hemisphere Australia is being hit with its own severe weather: tremendous rainstorms and cyclones causing unprecedented flooding and hardship. What is going on with all this weird weather? Could it be due to global warming effects? Some say that these are climate change effects, and that global warming causes an increase in severe weather events.

Climate change models predict that the earth will warm as we put increasing amounts of carbon dioxide into our atmosphere. But the sophisticated models that predict future weather patterns taking into account the global warming effects also show increasing extremes of temperature and precipitation and severe weather activity. This would lead us to wonder if all the severe weather of the last few months is indeed due to climate change effects.

It seems paradoxical, but the fact is that any one storm event cannot be directly attributed to global warming causes, and yet an increase in average storm activity can indeed be attributed to it. How is this possible? Well, climate is all about statistics and probability. People often say things like "How can they predict what the weather will be like in 50 years when they can't even get the forecast right for next weekend? The truth is that long range climate models do not attempt to predict what the weather will be like in any given spot on any given day; they only forecast trends and averages. For example, they predict what the average temperatures will be over a season in a broad region, and what the average rainfall will be in a given year and region. They can forecast how many severe storms will occur in a year on average, but not the time or place of any particular storm.

What about all this snow - more than usual, how can that weird weather be consistent with global warming effects? While it may seem counter-intuitive, it is not inconsistent with the global warming trend that is underway, and might even be caused by climate change effects. Remember, winters are normally cold anyway, and in many regions the average temperatures can go up a few degrees and still be well below freezing. In fact, in some northern regions it is often said to be "too cold to snow today"-because colder air cannot hold as much moisture. So at those times and places warmer temperatures could directly lead to more snow. But consider this: even if it is actually colder in one part of the word in the winter, the average global temperature could still be higher-just do the math! So even if climate change effects are not causing the weird weather extremes, a colder winter does not refute that global warming effects are occurring. Even without averaging over the whole globe, a place with hotter summers and colder winters could still have a warmer average temperature over the year (if the summers are a bit longer or hotter by more than the winters are long or cold).

We don't have to do the math, because there are organizations that do that for us, and they tell us for example that 2010 was indeed warmer, in fact it tied (with 2005) for the warmest year on record! That is a more obvious global warming effect, regardless of whether or not you believe that climate change effects include an increase in severe weather.