One of the favorite arguments of climate-change deniers is “but it was warmer in the late 90s.” In fact, the odds are good that I’ll get that argument from George Will on This Weak tomorrow. I basically know the answer: temperature is a noisy time series, so if you pick and choose your dates over a short time span you can usually make whatever case you want. That’s why you need to look at longer trends and do some statistical analysis. But I thought that it would be a good thing to look at the data myself.
So here’s average annual global temperature since 1880, shown as .01 degrees C deviation from the 1951-80 average.
What this tells me is that annual temperature is indeed noisy: there have been many large fluctuations, indeed much larger than the up-and-down in the last decade or so. But the direction of change is unmistakable if you take the longer view. The fitted line in the figure is a 3rd-degree polynomial, but any sort of smoothing would tell you that there is a massive upward trend.
Of course, trend-spotting is no substitute for causal modeling; and the models are getting truly scary in their implications.
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Krugman went a bit further on it today:
Another note on short-term pseudo-trends
As I noted in my previous post, a lot of climate-change denial rests on spurious short-term comparisons: you pick a warm recent year, say 1998, and say “well, the trend has been down since then.”
If you want a simple analogy to see why that’s wrong, consider daily temperatures over the course of a year. Here’s data on average daily temperatures in NYC. If you look at the months of April and May, you find that the warmest day was — April 26. So clearly it’s nonsense to say that New York’s weather is getting warmer as we move into summer ….
http://krugman.blogs.nytimes.com/2009/06/27/another-note-on-short-term-pseudo-trends/Sadly, when it come to the cult of denialism- this sort of reasoning falls on deaf ears.