Wednesday, November 11, 2009

Explaining climate vs weather

A person wrote a comment in a Treehugger entry that seems to have not recognized the difference between temperature and climate forecasting. (At least that was my perception.) This is something that people seem to have a problem understanding, so I decided to make the effort to describe what the difference is. Even when you say that climate is the long-term weather patterns, that doesn't really make sense for lots of people; that definition of "climate" remains a string of words without a significant meaning, especially since climate predictions usually revolve around temperature values, which (at least in my head) makes it seem more akin to concepts of weather.

Starting off, weather forecasting is determining the temperature, wind, cloud cover, and precipitation conditions on a day (or hour) in the future. Climate forecasting is determining the character and timing of the seasons.

Even if one knows what the climate is, that knowledge doesn't help one too much with weather forecasting. For example, if one lives in Southeast Michigan (as I do), then one would know that the climate of the region is that of four seasons, with relatively cold winters and warm summers; rainy springs and falls; snow melt usually coming around March; prevailing winds from the west-southwest; a mean air temperature of around 50F; and an average monthly precipitation of 2.8 inches. However, knowing all of this doesn't allow one to know what the temperature, precipitation, and wind speed will be tomorrow or even this weekend. All one can say with absolute confidence is that it is more likely to be like weather expected in the autumn than it is weather that would expected any other time of the year. In other words, the climate model of ascribing characteristics of a "Continental Temperate Zone" tells one as much about weather patterns occurring now as future climate models tell one of future weather.

In the same way that one cannot predict the weather this weekend even though one knows the climate of this region (although I can make informed predictions based on knowledge of my regional climate), one cannot predict the weather of the future from climate models. However, one can say that if average annual temperatures increase by 2C (~3.6F), certain trends in weather patterns (i.e., physical responses around the globe, including glacial melting leading to sea level rise, warming of oceans leading to more intense storms, melting permafrost leading to releases of formerly trapped methane, etc.) will be seen.

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