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Tuesday, September 25, 2007

Data gathering

Obligatory disclaimer...

You know, life would be a whole lot easier if I'd just accept whatever I was hearing in the media, or what other people are telling me, in regards to AGW and climate change. But nooo... I've gotta go and research this stuff myself. Now I'm finding myself questioning assumptions I've had about all sorts of things!

Take temperature data. I regularly check the local weather for the day when making plans to go out - it makes it easier to tell the kids to wear a jacket if I can say the weather office says it's going to be chilly, than if I tell them it's chilly, y'know? *L* In fact, we've got WeatherEye downloaded on our computers. It's available through The Weather Network. A tiny icon on the task bar shows the current temperature. A mouse-over gives a bit more information. Clicking on it opens a window with short and long range forecasts and tabs to click that'll take you to web pages for weather maps, road conditions, etc. A useful little thing.

The other place I go to get my weather information is the Government of Canada weather office. I love this site! Aside from finding your local weather conditions, you can look through the databases and go back over a particular weather stations data for decades. I could easily spend hours there. The biggest surprise I had there, though, was discovering the weather station we get our temperature readings from has been in existence for a very short time.

I've noticed a couple of things, though. These two weather services don't always agree. Yesterday, for example, as the kids and I were heading out at noon, WeatherEye told us it was only 4C. The weather office, however, showed me that the temperature at that time was 11C. Why the difference?

Well, the weather office uses readings from a weather station located near an airport, outside the city. I have no idea where the Weather Network gets their reading from, but it's obviously not from the same station. Wherever their data is recorded, the weather there isn't always the same. That stands to reason. After all, we're just a few blocks from downtown and there have been days my husband has been hailed on while walking to his office, while outside our balcony we've still got sunshine.

So then I get to wondering out all sorts of other things. Take "normal" temperatures. When watching the weather report, you'll often hear that a temperature is X amount above or below "normal." I had always assumed that "normal" had meant "what the temperature usually is." It turns out that "normal" doesn't mean the same thing in weather recordings than it does in usual language use. "Normal" turns out to be just an average. Temperature data from the past 30 years is averaged out. Why 30 years? No real reason, except perhaps that most weather stations have been recording for at least that long. It's an arbitrary time line. They could just as easily have used 10 years, or 50 years.

So the temperature data for a specific station is averaged out (mean average, more specifically), and that average is labeled "normal." Temperature readings above or below that are called "anomalies." I'd always thought an anomaly was something that was unusual, strange, not the way things should be. Not in temperature data, though. With temperature data, an anomaly is simply a reading that isn't "normal," and "normal" is just an average. So "normal" temperature isn't actually normal, nor are temperature variations actually "anomalies" according to the usual ways those words are used. Unfortunately, when we hear the weather reports, no one bothers to explain that, so when we're told a temperature is above or below "normal," we tend to think that there's something unusual happening, when in reality, there's nothing strange happening at all.

Then there's the temperature data itself. Another assumption I'd made is that temperature data used for such things like calculating the global average temperature was what the actual temperature readings were. Wrong. They don't work with raw data. The raw data is adjusted for various things, like the Urban Heat Effect. Ok, that makes sense - but who determines which data needs to be adjusted, and by how much? If you've been following Climate Audit at all, you'll see exactly what a problem that actually is. If you check out Surface Stations even briefly, you can see that even the raw data is questionable!

Then there's the weather stations themselves. As I posted about earlier, not all countries have the same requirements for these, as Germany takes their temperature readings in the shade, while North American weather stations are (supposed to be) located in the open. Again, I find myself facing my assumptions. With my handy WeatherEye giving me updated temperature readings continuously, I assume these stations are all monitored continuously. Some are, but this is very recent. Here's a brief overview of the various definitions.

First, a typical weather station. There used to be a great many of these in the past, but there's quite a few less, now. Many have been abandoned for various reasons, from lack of funds to lack of volunteers to go out and check the data. That's right - these stations depended on unpaid volunteers to go out to wherever the station was located and record the data on a daily basis.

What about automated stations? Yes, they exist, too, "... either to save human labour or to enable measurements from remote areas." They have a problem, though. "Unlike manual weather stations, automatic weather stations cannot report the class and amount of clouds. Also, precipitation measurements are a bit problematic, especially for snow, as the gauge must empty itself between observations. For present weather, all phenomena which do not touch the sensor, such as fog patches, remain unobserved."

Then there's the equipment used. Many stations use the Stevenson screen. These stations, however, give a single reading - whatever the temperature is at the time the volunteer reads it. Newer MMTS equipped stations give two readings - a maximum and a minimum. Those numbers are then averaged to get the reading for the day. As long as they're not located next to air conditioning units, buildings, or on parking lots, the data should be fine.

In my faith in scientific accuracy, I never imagined that the basic data was so loose and flexible, with so many gaps and potential errors! I suppose, had I stopped to think about it, I should've known better. I certainly know how much temperatures and conditions can fluctuate in even a small area. Why I assumed "officially" gathered data would somehow not be effected by this, or accounted for, I have no idea.

I guess it was just easier that way.

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