Global warming?

[Hank Kroll]

(Source: stardateonline, 7/4/08)
>
> Too hot outside for ya? Here's a cooling fact. Earth is at aphelion
> today, which marks its farthest point from the Sun for the year. We
> are more than one million miles farther from the Sun than the average
> distance of about 93 million miles.
>
> //end//

That raises an interesting question: How much warmer would Northern
Hemisphere summers be if, at this time of year, earth were at
perihelion rather than aphelion? Has anyone done an estimate? Bear
in mind that, about 10,500 years ago, earth did reach perihelion at
this time of year.

It's so cold we can't even grow potatoes here in Alaska!

[David Williams]

-> That raises an interesting question: How much warmer would Northern
-> Hemisphere summers be if, at this time of year, earth were at
-> perihelion rather than aphelion? Has anyone done an estimate? Bear
-> in mind that, about 10,500 years ago, earth did reach perihelion at
-> this time of year.

-> It's so cold we can't even grow potatoes here in Alaska!

I was in Iceland a couple of weeks ago, probably further north than you
are. The weather was sunny and about 20 degrees Celsius. Your cold
summer is certainly not typical of the whole northern hemisphere.

The eccentricity of the earth's orbit is about 0.0167. So, at
perihelion, it's 1.67% closer to the sun than average, and the reverse
at aphelion. So the difference is 3.3%, which means that the intensity
of sunlight is about 6.6% greater at perihelion than aphelion. So the
equilibrium temperature should be fourth-root-of(1.066) times higher at
perihelion than at aphelion. That comes to 1.016. So we're back to 1.6%
higher. The temperature is about 300K, so the difference would be about
5 degrees Celsius.

Winters, of course, would be similarly colder.

dow