July 6, 2007
Headed for the Heat
Here's a fascinating fact for impressing your friends this evening. At 8 p.m. the earth will be at its furthest distance from the sun for the year. The planet's revolution around the sun is slightly elliptical. Today we're about 94.5 million miles from the sun. Early next January we'll be only 91.5 million miles away (as demonstrated by this awesome graphic). The date of the aphelion has only a slight affect on seasonal temperatures, which are largely determined by the 23.5 degree tilt of the earth with respect to its orbital plane. The date of the aphelion changes slowly, it'll occur in the second week of July in 400 years, and in January in several thousand, and is one reason why the Ice Ages will appear again in 20,000 years or so.
No Ice Age this weekend! The last seven days have averaged 5.5 degrees cooler than normal. Today's temperatures will be about normal. There's a slight chance of an afternoon shower or thunderstorm today as a cold front passes through town. The front will bring drier, not cooler, air. Tomorrow's high will be in the upper-80s.
Saturday will be the nicest day of the weekend by far. The Bermuda High reasserts itself Sunday, bringing us a blast of hot and humid weather. High temperatures Sunday and Monday will be around 92-94. With the humidity that'll push us close to a Heat Advisory. Nowhere near the heat seen out west but still mighty unpleasant. The heat may break by Tuesday. Let's hope the floating pool is fixed before then!
Today's forecast high temperatures (red is 100 degrees or hotter) from the National Weather Service.
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Interesting post, but I am curious how the date of the aphelion has any impact on the overall earth climate. Can you update the post to point toward a source that will explain why Earth will go through another Ice Age in ~20,000 years?
Al Gore III is going to do commercials for Toyota. "Yes, you can get a Prius over 100 mph!"
You weren't kidding about that awesome graphic. Awesome.
so...is this for or against global warming?
Joe, that's kind of a real oversimplification of the whole ice age process. Granted, you did say "one of the reasons", but they certainly are not predictable like you imply. http://en.wikipedia.org/wiki/Milankovitch_cycles, for more info...
My intent wasn't to explain the ice ages, but to expand a bit on why the aphelion is of importance to long-term climate but not day-to-day weather.
A slightly less simplified, but still way simplified explanation is that ice ages come and go in response to three cyclical orbital variations: changing date of aphelion/perihelion, changing eccentricity of orbit around sun, and changing obliquity, or tilt of the earth. The three cycles change on different time scales ranging from 26,000 to over 100,000 years.
When the orbital cycles align such that there's more snow falling in the Northern Hemisphere winter and less melting of snow cover in the summer, glaciation can occur rather rapidly.
NASA has a decent explanation - http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/milankovitch.html