Science Scoops: And…Reflections of Earth's Climate
by Stephen James O'Meara
Wondering how earth's climate may be changing over the years? Well, how about keeping an eye on the moon? Yup. That's what researchers did in the late 1920s, and that's what Philip R. Goode (New Jersey Institute of Technology) and his colleagues did more recently. Actually, Goode and his team are not directly watching the moon. Instead, they're watching sunlight that has been reflected off the earth and onto the moon's “bright” side when it just happens to be in shadow, a phenomenon called “earthshine.” You see earthshine best when the moon is in a crescent phase; it's the “old moon in the new moon's arms.” In essence, the scientists are using the moon as a mirror, one that will reflect changes in earth's atmosphere.
Here's how it works. The amount of sunlight our planet bounces back into space reflects how much cloud, atmospheric dust, and snow is covering the earth. Any radiation not being reflected is being absorbed. This means that if the earth isn't being as reflective as normal, earth's climate must be getting warmer.
As reported in Sky & Telescope magazine, Goode says that on average the earth reflects 30 percent of the sunlight hitting it. But recently our planet seems to be a bit brighter than it was in 1994–95. What does this mean?
Is the earth getting colder?
Well, stay tuned, because the earthshine measurements will have to continue for many more years before the researchers can draw any conclusions.
- How does the temperature of Earth's atmosphere affect earthshine? Write a few sentences to explain your answer.
[anno: When Earth's atmosphere is warmer, more sunlight is being absorbed by Earth, so less sunlight is being reflected from Earth onto the Moon. When Earth's atmosphere is colder, it means that less of the Sun's warmth is penetrating through Earth's atmosphere, and more light is being reflected from Earth onto the Moon.]
- How would earthshine be different if Earth's atmosphere refracted the Sun's light rather than reflecting it? Why?
[anno: Answers may vary but could include that the Moon might not shine as brightly if the light hitting its surface were refracted from Earth's atmosphere rather than reflected. If refracted light were hitting the Moon, it might have to travel farther than if it were directly reflected from Earth's surface, and the light might be a little weaker.]
- Imagine that the temperature of Earth's atmosphere changed so much so that very little sunlight was reflected back toward the Moon. How would life be different if the Moon stayed dark? How would people and activities be affected?
[anno: Answers will vary.]