Climate Changes

 The Colorado Front Range is a cloud factory. Moist air is lifted, sent East over the High Plains, and becomes cumulonimbus clouds.

Lots of Virga (precipitation than evaporates before hitting the ground) that will get a pilots attention in a hurry.

http://en.wikipedia.org/wiki/Virga

Moving to the East it grows.

And, too often, becomes this.

I'm a man made climate warming skeptic. One good sized volcano erupting will put more crap into the atmosphere that all of the industrial revolution (except, maybe, fluorocarbon).

http://www.thenakedscientists.com/forum/index.php?topic=15196.0

What I do know is the climate does change. In the 1960's, Denver area summer cumulus tops were in the 35,000' range. Today. they are often in the 65,000' range. My question is this. Is this a normal, historical cycle? If not, what is  causing the change?