SCIENCE

Weather vs. Climate

August 4, 2009

Seattle and the Pacific Northwest are frying under a heat wave this summer. In New York, it’s so cool that the New York Times has called it “the summer that isn’t.” And Texas is suffering under the most severe drought since the 1950s.

What does this all mean for climate change?

Absolutely nothing.

Every time we write about climate change, someone writes in saying that they are shocked that Smithsonian would perpetuate such a myth. Don’t we know about the record cold/snow/rain/etc. in Minnesota/North Carolina/Utah/etc.? Obviously, there are some people who do not understand the difference between weather and climate. Let’s start with the dictionary definitions:

Weather: the state of the atmosphere with respect to wind, temperature, cloudiness, moisture, pressure, etc.

Climate: the composite or generally prevailing weather conditions of a region, as temperature, air pressure, humidity, precipitation, sunshine, cloudiness, and winds, throughout the year, averaged over a series of years.

In short, weather is a data point. Climate is a collection of data.

You can think of it like the economy. I can tell you that the Dow is up 112.61 as I write this, at 9,284.22. This is the weather (partly sunny, 84 F). But it doesn’t tell you anything useful about the economy as the whole (like the weather conditions don’t tell you anything useful about climate). A graph of the Dow over the last year, showing a terrifying decline followed by a steady rise, begins to tell the story of the last year. But to get a true picture of the economy, we’ll need to look at lots of other bits of data, like consumer confidence, unemployment rates and durable goods orders. It’s complicated, messy and hard to understand. That’s climate.

Now, if you make changes to the country’s economic situation, for example, by raising taxes, that is going to have some effect on the economy as a whole. Economists will crunch the numbers and come out with predictions. They won’t all be the same, but they will probably trend toward some particular end.

Adding carbon dioxide to the atmosphere is akin to raising taxes. We’ve changed the climate situation. And while these climate models—which are far simpler than economic models and more certain—may not agree on the specifics, the general trend is that temperatures are going to rise.

And they have been rising. And more than that, we can already see the effects of that rise. Just read the magazine: We’ve featured melting glaciers, melting permafrost and changes in plant and animal distributions in the Andes and, closer to home, the Northeast, to name a few.

So please don’t write to us to say that we’re neglecting the latest weather superlative. We’re not. We just have our eyes on the bigger picture—climate.