Global climate change
A Simple Experiment
4/19/2010, 7:55:35 AM
Mike Smith, who is the CEO of WeatherData Services, Inc, which by the way is an AccuWeather company located in Wichita, KS, recently performed an interesting experiment in his own back yard, and he asked me if we could post this on the global warming blog. Here is Mike's post.............
Recently, several articles have appeared in the popular press pertaining to "black carbon" or "soot." In the context of melting glaciers, at least one of these articles stated that the soot warmed the atmosphere and contributed to global warming. This is a misstatement as to the actual effect of soot on frozen surfaces such as glaciers and polar ice caps.
In order to understand the effect of soot, the concept of "albedo" has to be explained. The definition of albedo is "The ratio of the outgoing solar radiation reflected by an object to the incoming solar radiation incident upon it." Fresh, pure white snow has an albedo of nearly 100% -- in other words, just about all of the solar energy striking the snow is reflected back into space. Since the heat is reflected rather than absorbed, the solar energy has relatively little melting effect.
However, if the 'color' of the snow is darked by soot, the albedo drops dramatically. Since the soot absorbs some of the radiation that otherwise would have been reflected, heat transfers from the soot into the snow resulting in an accelerated rate of melting. It is important to state that this heat transfer can cause melting to increase even if the ambient temperature remains constant.
I conducted a backyard demonstration on Christmas Eve 2007.
Here is a photo of fresh snow cover in my backyard over which I had tossed some eight month-old fireplace ash under a totally blue sky
Keeping in mind this demonstration is occurring just two days after the winter solstace (meaning the albedo effect is less than it would have been under clear skies in February or March), in just one hour, the greater melting in the ash-covered areas is already apparent:
After four hours, the ash-free area has a depth of 5.5 inches
At the same time, the ash-covered areas have a depth of about 2.5 inches. Multiple measurements were taken (note ruler hold about an inch in front of ruler) which yielded an average depth of 2.5 inches.
The areas without soot melt about 0.5 inches of snow during this 4-hour period while the soot-covered areas melt 3.5 inches.
For visual comparison purposes, note the ruler hole in the non-ash-covered snow above the shadow.
Even tiny amounts of soot pollution can induce high amounts of melting. There is little or no ash at upper right.. Small amounts of ash in the lower and left areas of the photo cause significant melting at the two-hour mark in the demonstration.
Any discussion pertaining to melting glaciers or icecaps must consider the accelerated melting caused by soot pollution in addition to any contribution from changing ambient temperatures.
Mike's experiment will also be featured on Roger Pielke Senior's blog.
Photos: Copyright 2007, Michael R. Smith
Mike Smith is CEO of WeatherData Services, Inc., An AccuWeather Company. Smith is a Fellow of the American Meteorological Society and a Certified Consulting Meteorologist.
NOTE: I will be out of the office Wednesday and Thursday as I drive back to Indiana to finally bring my wife and new daughter home after almost 4 weeks. My daughter is eating well and has reached the 6 lb mark. Just so you know, I do not expect there to be an updated blog on Thursday. Paul and Marlene will update the comment section while I am gone. I should be back on Friday. Brett.
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