If not for clouds and nitrogen, Earth could be an uninhabitable hell right now

[DainBramaged]

With the explosion of exoplanet discoveries, researchers have begun to seriously revisit what it takes to make a planet habitable, defined as being able to support liquid water. At a basic level, the amount of light a planet receives sets its temperature. But real worlds aren't actually basic—they have atmospheres, reflect some of that light back into space, and experience various feedbacks that affect the temperature.

Attempts to incorporate all those complexities into models of other planets have produced some unexpected results. Some even suggest that Earth teeters on the edge of experiencing a runaway greenhouse, one that would see its oceans boil off. The fact that large areas of the planet are covered in ice may make that conclusion seem a bit absurd, but a second paper looks at the problem from a somewhat different angle—and comes to the same conclusion. If it weren't for clouds and our nitrogen-rich atmosphere, the Earth might be an uninhabitable hell right now.

The new work focuses on a very simple model of an atmosphere: a linear column of nothing but water vapor. This clearly doesn't capture the complex dynamics of weather and the different amounts of light to reach the poles, but it does include things like the amount of light scattered back out into space and the greenhouse impact of the water vapor. These sorts of calculations are simple enough that they were first done decades ago, but the authors note that this particular problem hadn't been revisited in 25 years. Our knowledge of how water vapor absorbs both visible and infrared light has improved over that time.

Water vapor, like other greenhouse gasses, allows visible light to reach the surface of a planet, but it absorbs most of the infrared light that gets emitted back toward space. Only a narrow window, centered around 10 micrometer wavelengths, makes it back out to space. Once the incoming energy gets larger than the amount that can escape, the end result is a runaway greenhouse: heat evaporates more surface water, which absorbs more infrared, trapping even more heat. At some point, the atmosphere gets so filled with water vapor that light no longer even reaches the surface, instead getting absorbed by the atmosphere itself.

http://arstechnica.com/science/2013/07/clouds-nitrogen-may-be-key-to-preventing-a-runaway-greenhouse-on-earth/

[longship]

1. We ignore this at our peril.

And make no fucking mistake about it. Except for the climate scientists, who are becoming ever more insistent that we may be in deep poo poo, nobody pays any attention to what may be the most important question humans have ever asked. What happens when we ignore multiple lines of evidence that universally point to a world much less conducive to life as we've known it?

But the oil and coal industries have the answer? James Inhofe?

[AverageJoe90]

3. I don't see what nitrogen in the atmosphere has to do with your scenario, TBH.

Regardless of all these nutty fringe theories that might be running around, Earth is NOT going to undergo a total runaway greenhouse at any point that we can possibly concieve of. In fact, the only thing that COULD turn Earth into a giant rocky fireball, outside of all the nitrogen magically disappearing, would be the Sun going supernova, and that isn't happening for another 5 billion years or so.

[bananas]

2. If not for six inches of topsoil and the fact that it rains, we'd be toast.

Old Chinese saying.

[phantom power]

4. I'm confident we can overcome this and make Earth an uninhabitable hell anyway

[Judi Lynn]

5. It would be a snap if we were all Republicans! They've come so far, already. n/t