Bill, it's funny you mentioned John Coleman, and this is the perfect place to put this quickie story.
I lived in the tiny little mountain community of Boulevard, CA for 15 years. Elevation at my particular little pad there is 3,840 ft.
On June 30, 1994, I was happily tending a garden complete with pretty much everything a vegetable gardner grows ~ lettuce (the good kind), radishes, tomatoes, peppers, Swiss chard, all that.
On the morning of July 1, 1994, the temperature dropped to 29 degrees.
I called John Coleman, who was and still is the weather guy at K-YOO-SI TV (and the founder of the Weather Channel). We had the usual nice chat. John is a great guy, has a clue, has lived a long life and has life, as far as I'm concerned, in perfect perspective.
He made my call the "question of the day" on the newscast. What was the coldest temperature in San Diego today? a) 43 b) 38 c) 29
This was July 1. In San Diego.
Of course there was a short discussion about my dead peppers and tomatoes after that.
Now fast forward to 2009, I live in Sparks, NV, at 4435 ft. elevation, and my friends back in Boulevard have had more snow this year than we have had up here, plus they had a nasty ice storm over Christmas that broke up the pine and oak trees pretty bad. Meanwhile up here, well let's just say a 4X4 hasn't been needed (yet).
Bee made a mention of visible phenomenon. What you see isn't necessarily what you get with this planet, but occasionally you can. Here in Truckee Meadows I would worry less about CO2 and more about that brown goo that covers the valley during inversions. A couple weeks ago the barometric pressure stayed above 30.70 for more than a week and you literally could not see across the valley, the smog is so bad. Plus your skin itches and you wind up smelling like cocoa butter.
When hiking to Sawtooth out of Mineral King, you see the same thing...late in the day the smog creeps up out of Bakersfield and the view west disappears. I haven't noticed smog so bad in Yosemite but it is there.
BTW, smog seems to make the Firefall a little better. Some good with the bad, I guess. Firefall is coming up as what little snow we have is melting quickly!
Here's a photo I have not previously put online. This is from the Yosemite Falls trail circa March 2005: