Sunday, July 11, 2010

Water Temperatures

This summer has been hot. It feels much hotter than last summer, although last summer was one of the coldest in decades in some places. This summer, however, feels a lot hotter than last summer, and perhaps hotter than usual.

I observe temperatures through a variety of non-scientific means. One of my favourite, and least scientific, is the temperature of my swimming pool in North Carolina. Water changes temp a lot slower than air, so it's a good medium to "smooth out" daily and weekly fluctuations.

This summer, my pool got hotter than usual quicker than usual - it was up to the high 80's in early June, which was a notable spike. I expected it to stay hot because of the heat wave that has hardly been broken since then. But something strange happened: it dropped back to the high-70s/low 80s in late June, where it has been for the last several days, even though the daytime temps seem hotter than usual to me. I absolutely don't know what this means or how it happened.

Last year the pool never got above the low-80s all summer, whereas two years ago it went to the high 80s in mid-June and stayed there until September. It seems like its been hot, but the pool doesn't seem to know it.

Another thing I look at is sea surface temps in the Florida Keys. I expect it to be mid-high 80s in July and this week it's been 82-84 - seemingly a couple of degrees cooler than usual. I looked at historical data, however, and the temps are actually very close to historical averages for this week in July, according to the data I found. Unfortunately, NOAA's weather stations are notoriously unreliable in the Keys and a lot of data is missing, which is very frustrating. There does, however, seem to be a warming trend since 1988, which is the first year of data for the stations I looked at (SMKF1 and SANF1). The chart below would seem to indicate that warming trend is strongly indicated by the global average.

Lately I've learned about how temperatures are measured and studied. The "UAH" global temperature average is the community standard. "UAH" refers to the University of Alabama at Huntsville, where they work hard to keep track of these things, mainly relying on NOAA satellite data, which we have only had for about the last 30 years.

Here is a helpful interactive chart from UAH on recent temperature trends. It shows 2010 as warmer than usual even for recent years, which is strongly suggestive of a warming trend, although the graph has turned down in the last few days and we are now (as of this week) a little cooler than last year and about the same as the last few years' average. Interestingly, this is just for sea surface temperature. If you go up in the atmosphere, the picture changes dramatically. 2010 is colder than many recent years at higher altitudes (play with the altitude selector on the left side of the UAH interactive chart to see it). I have absolutely no idea what this means or why it is so - maybe someone else does?

But I am hoping my unscientific observations of temperature are correct and the Caribbean and Gulf of Mexico are a little cooler than usual because that will probably mean a comparatively benign hurricane season. Every year recently the Colorado State University predicts an "active" hurricane season but 2008 and 2009 were extremely quiet - well below average. As hurricane season is coming right up, we shall soon see...

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