I Inadvertently Give America a Bad Reputation on Global Warming.

One of my flatmates remarked that she believed that the unusually cool weather in London last week was because of global warming. I said that although I that might be true, we don't really understand how global warming will affect local weather conditions well enough to make assertions like that. She countered by claiming that the weather in London this winter was so abnormal as to constitute strong evidence for global warming. I said that I suspected it was well within the bounds of normal random weather behavior (and that's what prompted me to look at the data that led to my last post).

I learned today that when she told her roommate that I had said this, her roommate responded by saying, "that's just the response that you should expect from an American." It turns out that she interpreted and passed on my objection as saying that I didn't believe in global warming. And although I repeatedly told her that I believed it was a problem, and that there was good evidence pointing us towards the danger of global warming, unusual weather for a week -- or for a year, or for ten years -- in London did not constitute good evidence. I showed her my graph of historical temperatures where you can see clearly that although the weather has been unusual for the last ten years, it has been as "unusual" many times before, including many times before the industrial revolution when it was certainly not the effect of human carbon output.

It was odd how unable she seemed to decouple the two ideas. She kept challenging me with questions like, "don't you think that global warming would cause temperatures to rise?" "Don't you think we are changing the environment with pollutants?" And most significantly, "don't you think global warming will cause unpredictable weather behavior?" The answers are yes, yes, and yes, but that doesn't mean that everything that could be explained by global warming is evidence for it, especially in light of the last question -- the effects will be unpredictable, especially in something like weather, with a very high noise-to-signal ratio.

I'm not very sure I made her understand this even in the end. I'm afraid she's going to continue going around telling people about the American in her flat who doesn't believe in global warming.

By the way, although my test for a structural break in average temperature gave crazy results (suggesting that modeling weather as a normal distribution with a mean that changes reasonably smoothly is a flawed model), there is a statistically significant warming trend in the data that I have. It cannot be observed in only a handful of the data, but in a regression over all the recorded temperature for England, it appears that things have been getting gradually warmer in a way that is inconsistent with simple random chance. Again, this is not direct evidence for global warming per se, but it is more relevant than a single cool, rainy week in May.