You might think fouling your own environment with lots of toxic smog is a poor indicator of intelligence. But obviously, heavy smog on Earth is gift of the industrial revolution. Our modern machines blow out smoke as a byproduct of energy production. That smoke is distinct from natural molecules. Methane, coal, and oil may be produced by natural causes, but burning them to do work takes intelligence.

Methane is produced naturally in a number of ways. For years, astrobiologists have thought that spectra indicating methane on alien planets might provide a biosignature of microbial life. According to NASA’s Astrobiology Magazine, however, SETI researchers might be able to use methane as a sign of intelligent life, by differentiating between natural and fabricated methane signatures on distant planets:

Since life forms from the bacterial to the bovine to the human being pump it [methane] out as part of their normal daily activities, searching for methane lines makes sense. In the specific search for highly evolved life, however, something even better may be on the horizon — something that would tell us that not only is life flourishing, but fabricating. (Emphasis added.)

What does "fabricating" imply? Intelligent design, clearly. It takes machinery to produce certain atmospheric signatures, and machines are fabricated by minds for a purpose. Natural causes cannot burn methane to make smog. Nor do they generate the CFCs that damage our ozone layer. So here’s an indirect way to make a design inference, without having to scan the stellar radio dial for intentional broadcast messages.

If industrialized alien civilizations exist, Harvard Smithsonian scientists Henry Lin, Gonzalo Abad and Abraham Loeb contend that the best way to look for them may be in signs of environmental destruction that mirror our own….

So rather than wait for a signal that may or may not be coming in a form we may or may not be prepared to detect, Loeb, Abad and Lin suggest that we look for the effects alien civilizations are having on their home planets’ atmospheres.

There are a number of advantages to this approach. First, we are already searching exoplanet atmospheres for signs of life like methane. "It doesn’t take too much extra effort," Lin told astrobio.net, "to also look for signs of intelligent life."

The research by Henry Lin, Gonzalo Abad and Avi Loeb is available on arXiv, awaiting publication in the Astrophysical Journal. Unless these astrobiologists contend that our civilization is the result of unguided natural processes sans intelligence, they are implying that intelligent causes can be inferred from, of all things, pollution! It’s actually very instructive for ID theory. Who would have thought a blonde’s hairspray is a sign of intelligence?

In addition to needing no new instruments to find them, CF4 and CCl3F [two particular chloroflurocarbons] have another advantage: both are sensitive as well as specific for industrialized life. If found in an alien atmosphere, there’s pretty much only one way that they got there.

"These molecules are basically only produced by human[-like] activities," Abad told astrobio.net. "Whereas methane will be everywhere regardless of whether you are polluting or not. These markers target civilizations with advanced industry."

While primitive forms of life have their own biomarkers — like oxygen and methane — these molecules are too complicated for nature to, as Loeb put it, "do this on its own." However, at least for the moment, we can’t rush off and start looking for aliens by their hairspray.

If we could detect these particular CFCs someday, the point is, an inference to intelligent life would be inescapable. Intelligent-design theory never claims that phenomena worthy of a design inference are wise! They just need to go beyond the capabilities of chance and natural law.

The NASA article says that a simple signature of "hot methane," in fact, would be sufficient to infer intelligence. Instead of coming from bacteria or a cow’s rear end, hot methane would imply "gas burners" — intentional use of energy for intelligent purposes.

We can’t find these signatures yet, but they are detectible in principle. When the James Webb Space Telescope (JWST) launches in 2018, it may have that capability.

It won’t be easy to find an Earth-like planet around a white dwarf transiting at just the right angle, but once we do, Lin said, "We should check for crazy amounts of pollution."

With this model and a survey of white dwarfs in hand, when the JWST takes to the skies in 2018 we can begin an earnest quest for life as brilliantly self-destructive as we are. Until then, we continue to find more exoplanets whose atmospheric methane may hold the key to finding life sleeping on ocean floors or cooking over fires from millions of light years away.

Brilliantly self-destructive aliens can still be brilliant in their folly. ID doesn’t make an issue of that. It simply seeks to distinguish the activity of a mind from the activity of natural causes.

Elizabeth Howell at Live Science carries the implications further. In her piece "Alien Smog: How Pollution Could Help Locate E.T.," she quotes Lin stating that the aliens would be justified in making a design inference from observing Earth’s atmosphere:

"We consider industrial pollution as a sign of intelligent life, but perhaps civilizations more advanced than us, with their own SETI programs, will consider pollution as a sign of unintelligent [i.e., unwise] life since it’s not smart to contaminate your own air," study leader Henry Lin, a student at Harvard University, said in a statement.

So if minds "more advanced than us" can make a design inference from observations of nature, we can, too.

That Lin means "unwise" by "unintelligent" is clarified by his colleague Avi Loeb. Some pollutants are long-lived, and others are short-lived. If the short-lived pollutants have disappeared in an alien atmosphere, Loeb feels another design inference is warranted:

"In that case, we could speculate that the aliens wised up and cleaned up their act. Or in a darker scenario, it would serve as a warning sign of the dangers of not being good stewards of our own planet," study co-author Avi Loeb, a professor in the department of astronomy at Harvard, said in a statement.

This is rich! ID advocates stay away from moral judgments in their design inferences, but this Harvard astronomer has just inferred the wisdom and morality of aliens from the observation of gas ratios that are only detectible in principle. What was that about intelligent-design theory being a cover for creationism?