The January-June year-to-date tied with 2004 as the fifth warmest on record. The January-June 2009 map of temperature anomalies shows the presence of warmer-than-average conditions across much of the world's land areas, with the exception of cooler-than-average temperatures across Canada.
So apparantly it is only Canada that has been colder than average so far this year, although the dot closest to us in Waterloo is actually red indicating slightly above average temperatures.
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I have a question about the "base" period. Why is this period used? Is that the oldest complete data set for the world or something? It just seems rather arbitrary, and not representative of the typical climate. You'd think that the base would be a rolling 30-year window that changed from year to year to reflect the passage of time. Anyway, if you can give any insight about this, that'd be most appreciated.
...and I guess, why does it have to be 30 years anyway? Is that just to have it fall under the rules for being able to use the normal curve for stats purposes? Why not have more years included?
re: using the 61-90 base period
The problem with using a rolling average is that is it hard to compare data from say June 1998 to June 2008 if the underlying "base" period for comparison has changed. Saying that June 1998 was 0.2 degrees above the average and June 2008 was 1.2 below the average when the average has changed doesn't really tell you a lot.
The NOAA climate study uses the time period from 1961-1990 as the base while we use the 1971-2000 for the UW weather station comparisons. Generally those are two base periods that are used by most researchers. We use ours because that's when we have data from the Waterloo-Wellington airport.
The reason that 30 years is used as a base period as that was determined to be the length of record needed to mask out shorter term year to year variations.
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