Looking for aliens? Scan the skies for pollution

The search for extraterrestrial life, popularly known as SETI, has traditionally focused on searching for life in the universe by scanning the skies for electromagnetic radiation, like radio waves. A better way to search for extraterrestrial civilizations might be to look for industrial pollution, argues Sara Imari Walker, an assistant professor in ASU's School of Earth and Space Exploration and the Beyond Center for Fundamental Concepts in Science, in a Future Tense article for Slate magazine.

Industrial pollutants like the climate-altering chlorofluorocarbons (CFCs) that human industries produce could potentially be detected from hundreds of light years away. Pollution may be a more reliable sign of advanced civilizations than radio waves, which, judging by our own technological development, are only a temporary stepping stone to more advanced communications technology.

The Earth, which once broadcast a high volume of radio waves into space, is becoming increasingly "radio quiet" as we shift toward digital communications. If extraterrestrial civilizations are like us, they will only be using radio waves for 100 years or so, which seems like a long time, but on a cosmic scale is "hardly the blink of an eye."

Henry Lin of the Harvard-Smithsonian Center for Astrophysics, which has led the way in championing the hunt-for-pollution approach, has questioned whether discovering pollution in the farthest reaches of space would really be a sign of intelligent life.

Lin wonders if "civilizations more advanced than us ... will consider pollution as a sign of unintelligent life since it's not smart to contaminate your own air." Walker's perspective is that "our methods to search for extraterrestrial intelligence are an intimate reflection of ourselves."

In a historical moment where pollution and climate change are in the forefront of our global consciousness, it's not such a surprise that we are searching the skies for other civilizations in a similar situation.

"Hopefully," writes Walker, "we will one day enter a phase of human technological development where we will possess the insights to look for 'greener' little green men."

To learn more about pollution and the search for extraterrestrial intelligence, including hunting for alien garbage on the moon, read the full article at Future Tense.

Future Tense is a collaboration among ASU, the New America Foundation and Slate magazine that explores how emerging technologies affect policy and society.