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Fraser
2004-May-27, 08:23 PM
SUMMARY: Astronomers can measure the reflectivity of the Earth's atmosphere by watching "Earthshine" on the Moon. They found that a gradual dimming of this light from Earth reflected against the Moon matches the warming of the planet's lower atmosphere over the last two decades. The possibility that decreased cloud cover could cause climate change is still controversial, and many scientists are skeptical about this new research. Interestingly, the astronomers who produced this recent study have found that the trend is reversing, with Earthshine increasing again.

What do you think about this story? Post your comments below.

galaxygirl
2004-May-27, 09:54 PM
Nice article, Fraser! Global warming is an important issue that needs to be fixed soon, before Earth experiences greater effects (as many people who've been in the 'industrialize or explore thread know ;) ).

But I dont get how a decrease in cloud coverage and it's affect on climate can be controversial because when there's less clouds, Earth absorbs more heat, making it hotter. How would less clouds not affect the climate?

StarLab
2004-May-27, 11:06 PM
Interestingly, the astronomers who produced this recent study have found that the trend is reversing, with Earthshine increasing again.
I would expect that, given that people are becoming more aware about global warming.

GOURDHEAD
2004-May-28, 01:38 AM
How would less clouds not affect the climate?

Perhaps the controversy is over how much effect and in what direction. Clouds on the side of earth not lighted by the sun retain heat; on the sunlit side they reflect heat back into space as a net effect. Since warmer air retains more water than cooler air and since the drivers of weather patterns are not well understood nor diagnosed, it's not easy to predict whether cooling or heating will pertain. Some conditions will produce clouds shortly after the terminator passes a given longitude as night falls producing a heat retaining condition where particulate size and count, wind strength and direction and the attending pressure changes play major roles in a somewhat random way. During the daytime, clouds can be generated by putting excess water in the atmosphere again affected randomly by wind, particulate size and count, and pressure. Also, large storms, even at night, can evaporate large amounts of sea water into the atmosphere. The system is too chaotic to be reliably modeled; therefore extreme positions for or against global warming should be avoided. The measurement of earthshine reflected from the moon is a welcome measurable parameter but even here spectrum constituents are significant and may vary in a random way depending on the constituents in the earth's atmosphere that perform the filtering.

Global temperature changing deserves monitoring to the best of our ability and we should attempt to model courses of action to be taken to offset excursions from the mean of any significant magnitude---once we know what that means. Luckily the earth's natural feedback loops will handle most excursions but the reaction times could make it most uncomfortable for most humans. Also, it would be prudent to make sure that the cure is not worse than the malady.

Greg
2004-May-28, 03:50 AM
In my opinion the driving engine of global temperatures is the sun. Unfortunately, or fortunately depending on how you look at it, the sun's radiative output is far from constant. The variability of total output can be as high as 30 percent above or below the "norm" It is certainly true that carbon dioxide levels have risen and that they were high in previous warm periods such as during the time of the dinosaurs. But we do not know that the high carbon dioxide levels were a cause or an effect of global temperatures rising. I do think that higher carbon dioxide levels will have some effect that will raise temperatures, but that it pales in comparison to the effect of changes in solar radiation. The warming temperatures happen to coincide with an overall invrease in solar output in the same timeframe. In fact using a decade long scale solar output more closeley matches changes in temperatures than carbon dioxide levels. The best example is the cooling of the 1970s where carbon dioxide levels were clearly rising as global temperatures were falling (in concordance with falling solar output during that decade.) The test of course for this theory will be forthcoming. Solar output has been steadily falling and scientists such as John Daly knowledgeable about solar cycles are convinced it will continue to drop until a minimum around 2030. A noticeable drop in global temperatures should follow with a lag of perhaps 2 to 5 years from now. If solar output drops and temperatures do not then the carbon dioxide camp is right and we need to stop polluting asap.
I think t he Earthshine findings may be an effect of decreasing solar input into the atmosphere. There are some doubts, however about the methods and power of this study (too short a time frame and using data from different sources as if it were equally accurate.)

Eric Vaxxine
2004-May-28, 03:12 PM
I am not one to ignore the ill effects we ravage on our planet, but all it would take is one major volcanic eruption to pump more noxious gases into our delicate atmosphere than we would generate in 100 years of human industry.

Should we be more concerned with atmospheric purification? I have marvelled for many years over the planets ability to maintain an adequate oxygen supply for us. Never too much, always enough.

Or are we just lucky?