Words on Weather and Climate — December 16, 2010

Forecasting Climate 

by CRAIG JAMES 

Meteorologist Craig James, new Squire columnist

When it comes to forecasting the climate, many people say that since forecasters can’t get the weather forecast right for the next couple of days, how can they get the climate forecast right for the next 100 years? (They surely weren’t talking about my forecasts, were they?)

The response given by the climate alarmists is that they don’t have to forecast each day’s weather correctly. Over time, the weather averages out and just predicting the long-term trend of warmer or colder is not as difficult as predicting how much snow will fall from the next snowstorm. Therefore, we can have confidence in the climate forecasts out to the year 2100 and beyond. I don’t buy into that response and here’s why.

We pretty much know and understand all of the physics behind the atmospheric processes that control the short-term weather forecast. We can even construct computer models that do a fairly good job of representing how the atmosphere works over short time periods using the seven basic mathematical equations of motion for fluids. There are some approximations that have to be made when using these equations, but they work fairly well out to a couple of days. However, they do start to break down as they are run forward in time due to a lack of sufficient data and the inherent chaos of the atmosphere.

Once we get out beyond a couple of days, there are additional complicated forces that begin to have an impact on the forecasts, and it is these forces we don’t understand very well and can’t even begin to adequately model in our computers. These natural forces include such things as whether the Atlantic or Pacific oceans are in their cold or warm phase, whether there is an El Niño or La Niña in progress, how temperature changes affect cloud cover, cooling or warming from aerosols, solar influences, and many others.

An example of a natural force that over a long period of time affects the motion of fluids but has no effect in the short term is the Coriolis effect. The Coriolis effect is what causes our winds to rotate counter-clockwise around a low-pressure system in the northern hemisphere and just the opposite, or clockwise, in the southern hemisphere. Some people believe the Coriolis effect will cause water to rotate counter-clockwise down a drain in the northern hemisphere and clockwise in the southern hemisphere. That is just not true.

I mentioned this while I was on air at TV-8 a few years ago and from the indignant responses I received, you would have thought I had called someone’s mother a bad name. It must be one of those ingrained myths that refuse to die, like the one about raindrops being shaped like teardrops. The water spins down a drain far too quickly and rapidly for the Coriolis force to have an effect. Water can spin down a drain in either direction in either hemisphere.

I had a professor at Penn State who used to say, “The Coriolis force is so small, that it plays no role in determining the direction of rotation of a draining sink any more than it does the direction of a spinning CD.” You can read all about this myth and others on a fun web site he set up called “Bad Meteorology.”

But, back to my point: There are forces that play a large role in how the long-term climate changes, but have no effect on short-term weather events. Whether or not there is an El Niño occurring won’t have any influence on a forecast for tomorrow, but it will have a big influence on a seasonal forecast. And the most important point is that we do not understand and cannot model many of these forces that affect how the climate will change during the next 50 to 100 years. Therefore, given the difficulty in getting the forecast right for the next couple of days, the added complexities of what controls long-term climate make a forecast for the next 100 years… impossible.

Craig James has been retired since July 1, 2008, after 40 years of broadcasting television weather. He was chief meteorologist
at WZZM-TV for 12 years and chief meteorologist at WOOD-TV for 24 years. He is a graduate of Penn State University, where
he received a Centennial Fellowship Award. He was also honored as a Fellow of the American Meteorological Society.

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