June 2004
'Earthshine' And Climate Change
Scientists at Caltech and the New Jersey Institute of Technology (NJIT) have noticed that the Earth dims and brightens and that this may have an effect on climate change.
The team correlated data collected by NASA’s International Satellite Cloud Climatology Project for the period between 1983 and 2001 with the amount of light Earth reflects on to the dark side of the moon gathered over the last eight years.
The Earth’s average albedo (the amount of light reflected back into space, relative to the amount landing on it) was found to be changing and that it had been declining steadily from 1985 to 2001. The last three years, however, had seen this decline largely reversed and the Earth's albedo is now similar to pre 1995 levels, consistent with much cloudier skies.
This same period saw a massive increase in solar heating of the planet and as a consequence, an accelerated increase in mean global temperatures.
The scientists say that the warming effect of the apparent change in the amount of sunlight reaching the Earth's surface in the two decades is greater than the effect of greenhouse gas warming since 1850.
"At the moment, the cause of these variations is not known, but they imply large shifts in Earth's radiative budget," says Steven Koonin of Caltech. "Continued observations and modelling efforts will be necessary to learn their implications for climate."
Enric Palle, of NJIT, added: "Our most likely contribution to the global warming debate is to emphasise the role of clouds in climate change must be accounted for, illustrating that we still lack the detailed understanding of our present and past climate system to confidently model future changes."
The phenomenon of earthshine is not a new one; Leonardo Da Vinci explained it nearly 500 years ago. He realized that both Earth and the Moon reflect sunlight when the sun sets anywhere on the earth-facing side of the moon.
Print this page