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Monday, May 28, 2007

Apollo 15 data and Earth's energy budget

Shaopeng Huang, geophysicist with the University or Michigan is calling for an international effort to develop and deploy monitoring stations on the moon for the study of terrestrial climate change.

Science Daily — Poets may see "a face of plaintive sweetness" or "a cheek like beryl stone" when they look at the moon, but Shaopeng Huang sees something else altogether: the ideal location for a network of observatories dedicated to studying climate change on Earth.

Using data from an Apollo 15 experiment whose original intent was thwarted by unanticipated lunar surface conditions, the University of Michigan geophysicist recently showed that surface temperatures on the near side of the moon accurately record important information about Earth's climate system.

Based on his analysis, recently published online in Advances in Space Research, Huang is calling for an international effort to develop and deploy monitoring stations on the moon for the study of terrestrial climate change.

Global climate change is driven by an imbalance between incoming energy from the sun and outgoing energy from Earth. Without understanding the climate system's inputs and outputs---its so-called energy budget---it is impossible to tease out the relative contributions of natural and human-induced influences and to predict future climate, Huang said.

But detecting changes in the energy budget is difficult with existing ground-based and space-borne technologies, he noted. Fortunately, instruments left behind by the Apollo 15 astronauts---all U-M alumni, incidentally---inadvertently provided just the necessary measurements.


On the near side of the airless moon, where Apollo 15 landed, surface temperature is controlled by solar radiation during daytime and energy radiated from Earth at night. Huang showed that due to an amplifying effect, even weak radiation from Earth produces measurable temperature changes in the regolith. Further, his revisit of the data revealed distinctly different characteristics in daytime and nighttime lunar surface temperature variations.

This allowed him to uncover a lunar night-time warming trend from mid-1972 to late 1975, which was consistent with a global dimming of Earth that occurred over the same period and was due to a general decrease of sunlight over land surfaces. (Widespread ground-based radiation records from that period show that solar radiation reaching Earth's surface during that period decreased significantly, for reasons that are not completely understood.)

Huang's study demonstrated that signals from the energy budget of Earth's climate system are detectable on the moon and can be useful in monitoring and predicting climate change.

For that and other reasons, the moon is the perfect place for a system of observatories, Huang said. "As the sole natural satellite of Earth, the moon is an enduring platform without complications from atmosphere, hydrosphere or biosphere, and could provide records of Earth's radiation budget that would complement ground-based and man-made satellite records."

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