Clean Air=Global warming???

ALL-CLEAR IN THE STRATOSPHERE: Earth's stratosphere is as clear as it's been in more than 50 years. University of Colorado climate scientist Richard Keen knows this because he's been watching lunar eclipses. "Since 1996, lunar eclipses have been bright, which means the stratosphere is relatively clear of volcanic aerosols. This is the longest period with a clear stratosphere since before 1960." Consider the following comparison of a lunar eclipse observed in 1992 after the Philippine volcano Pinatubo spewed millions of tons of gas and ash into the atmosphere vs. an "all-clear" eclipse in 2003:

Keen explains why lunar eclipses can be used to probe the stratosphere: "At the distance of the Moon, most of the light refracted into the umbra (Earth's shadow) passes through the stratosphere, which lies 10 to 30 miles above the ground. When the stratosphere is clear, the umbra (and therefore, the eclipsed Moon) is relatively bright. On the other hand, if the atmospheric lens that illuminates the Moon becomes dirty enough, light will be blocked and the eclipse will appear dark."

This is timely and important because the state of the stratosphere affects climate; a clear stratosphere "lets the sunshine in" to warm the Earth below. At a 2008 SORCE conference Keen reported that "The lunar eclipse record indicates a clear stratosphere over the past decade, and that this has contributed about 0.2 degrees to recent warming."

This story reproduced from spaceweather.com (emphasis added)