Saturday, July 2, 2011

Georgia combined temperatures

When I first started looking at the temperature data for the individual states around the USA I began each post with a hypothesis, and then looked at the data to see if the hypothesis was validated. I haven’t done that for a while, but given that the temperatures in Northern Florida have been falling for a while, as have the average temperatures in Alabama, Mississippi, Tennessee, Kentucky, Louisiana, and possibly Arkansas I’m going to rise to the bait and hypothesize that the average temperatures in the state of Georgia have also fallen over the past 115 years. I will take the data from the 23 USHCN stations and, using the TOBS temperatures, see if the hypothesis is correct.

Location of the USHCN stations in Georgia (CDIAC)

There are three GISS stations on the list, in Atlanta, Augusta and Macon. Of these Atlanta and Macon have a sensibly full temperature record from the 1880’s, while Augusta falls into the class of those with data only since 1948.

Temperatures for the GISS station in Augusta, GA (GISS

With the exception of the spike in temperatures from 1981 to 1984, the town seems to have been cooling fairly consistently. Looking at the other two stations therefore, starting with Atlanta.

Temperatures for the GISS station in Atlanta, GA (GISS)

And there is the similar drop in temperatures between about 1948 and 1980 and the same sort of drop off since. So check with Macon:

Temperatures for the GISS station in Macon, GA (GISS

There is still a drop, though not as great (around 1962) and subsequent temperatures again have been trending down. So it does appear, from the GISS data that the hypothesis is correct, but with that initial eyeball of the data, it is better to run the actual numbers. Looking then at the composite picture from the three stations

Average temperature with time for the three GISS stations in Georgia

Although the more recent temperatures are holding relatively steady, the averaging, while showing the dip around 1965, does not show any recent decline. Looking at the USHCN homogenized average station temperatures for the state:

Average temperature with time for the 23 USHCN stations in Georgia – data homogenized

The difference between the two curves can perhaps be seen by the adjustments that GISS has made to the USHCN homogenized data.

Difference between the GISS average temperature and the USHCN homogenized temperatures for the state of Georgia

Looking at the raw data, as modified to adjust for time of observation (TOBS) the plot is a little different.

Plot of average Georgia station temperature with the raw data only corrected for time of observation

Now while this shows an overall decline in temperature over the century, it also shows a relatively steady increase in temperature since about 1970, so I am not convinced that the hypothesis has, in fact, been validated. Oh, well that’s why they call this research.

Georgia is 300 miles long and 230 miles wide, running from 81 deg W to 85 deg W, and from 30 deg N to 35 deg N. The average latitude is 32.71 deg N, that of the GISS stations is 33.24 deg N, and for the USHCN stations 32.7 deg N. Georgia rises from sea level to 1,458 m, with the mean elevation being 182.9 m. The average elevation of the GISS stations is 190 m, and for the USHCN stations 152 m.

Looking at the effect that the geography has on the station temperatures:

Georgia station temperature as a function of latitude

Looking at the correlation with longitude:

Change in station temperature with longitude in Georgia

Georgia is one of the states where, as the ground rises to the west, so the average temperatures fall. The elevation explains:

Change in station temperature with elevation in Georgia

The population statistics that citi-data quote are generally based on 2009 estimates, according to the sites I used, which explains why a five-year average seems to work best. There are a number of stations without full TOBS data in that period, however.

Change in station temperature with surrounding population in Georgia

I am not sure why the temperature data didn’t follow the expected trend, perhaps when I have this initial series finished, I’ll come back and look into that in more detail.


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