June 14, 2009
Will Earth Atmosphere Lose Nitrogen To Cool Planet?

CalTech profs are proposing that over the next couple of billion years as the Sun heats up and expands the life forms on Earth will gradually pull more nitrogen out of the atmosphere, lower atmospheric pressure, and allow more heat to escape, thereby delaying a big heating of the planet.

As the sun has matured over the past 4.5 billion years, it has become both brighter and hotter, increasing the amount of solar radiation received by Earth, along with surface temperatures. Earth has coped by reducing the amount of carbon dioxide in the atmosphere, thus reducing the warming effect. (Despite current concerns about rising carbon dioxide levels triggering detrimental climate change, the pressure of carbon dioxide in the atmosphere has dropped some 2,000-fold over the past 3.5 billion years; modern, man-made increases in atmospheric carbon dioxide offset a fraction of this overall decrease.)

The problem, says Joseph L. Kirschvink, the Nico and Marilyn Van Wingen Professor of Geobiology at Caltech and a coauthor of the PNAS paper, is that "we're nearing the point where there's not enough carbon dioxide left to regulate temperatures following the same procedures."

Kirschvink and his collaborators Yuk L. Yung, a Caltech professor of planetary science, and graduate students King-Fai Li and Kaveh Pahlevan, say that the solution is to reduce substantially the total pressure of the atmosphere itself, by removing massive amounts of molecular nitrogen, the largely nonreactive gas that makes up about 78 percent of the atmosphere. This would regulate the surface temperatures and allow carbon dioxide to remain in the atmosphere, to support life, and could tack an additional 1.3 billion years onto Earth's expected lifespan.

In the "blanket" analogy for greenhouse gases, carbon dioxide would be represented by the cotton fibers making up the blanket. "The cotton weave may have holes, which allow heat to leak out," explains Li, the lead author of the paper.

"The size of the holes is controlled by pressure," Yung says. "Squeeze the blanket," by increasing the atmospheric pressure, "and the holes become smaller, so less heat can escape. With less pressure, the holes become larger, and more heat can escape," he says, helping the planet to shed the extra heat generated by a more luminous sun.

Strikingly, no external influence would be necessary to take nitrogen out of the air, the scientists say. Instead, the biosphere itself would accomplish this, because nitrogen is incorporated into the cells of organisms as they grow, and is buried with them when they die.

In fact, "This reduction of nitrogen is something that may already be happening," says Pahlevan, and that has occurred over the course of Earth's history. This suggests that Earth's atmospheric pressure may be lower now than it was earlier in the planet's history.

Well, suppose the nitrogen doesn't naturally get removed from the atmosphere. Or suppose we (at least those of us who live long enough to get rejuvenated and live for extremely long periods of time) decide to prevent the atmospheric nitrogen depletion. What to do? The answer is obvious: increase the radius of Earth's orbit around the Sun. But how to do that? Any suggestions? It has to be done gravitationally I suspect. How to keep another body slightly tugging the Earth into a slowly increasing orbital radius?

Share |      Randall Parker, 2009 June 14 08:56 PM  Climate Trends

Billy Oblivion said at June 15, 2009 12:24 AM:

How about we just get off this mudball and learn to live w/out a planet?

Daniel said at June 15, 2009 5:18 AM:

Increase the orbit? Why go with half measures? It seems to me that restricting the fusion reaction occurring in the sun would both cool it down and allow it to burn for a few billion years more.

Ideally, we would cut the rate of fusion to a level where we could DECREASE the orbit to somewhere between Mercury and Venus and still be comfortably cool for twenty or thirty billion more years.

Nick G said at June 15, 2009 9:12 AM:

The first two ideas were good, esp reducing the rate of fusion burn. Find a way to scoop out hydrogen, and stash it elsewhere until needed.

In response to your question: if you have a billion years to increase the orbit, you only need a very tiny gravitational force. Its been a while since I've done orbital calculations, but I should think capturing a pretty small asteroid and pulling it ahead of the planet should do it.

Nick G said at June 15, 2009 9:39 AM:

Oh, how do you do that?

Well, first you capture and move the asteroid into an identical orbit, just ahead of Earth. Gravity will tend to pull the two together, so you apply a forward force to the asteroid.

How to move and apply a force to the asteroid? Well, in a few million years we'll find a lot of ways to do it, but right now NASA is using ion motors that would work ok.

How to use an ion motor ahead of the Earth, without hitting the Earth with the exhaust, and cancelling out the pull? Just have two motors, each emitting ions at an angles so they miss the Earth: the opposing sideways vectors cancel out, leaving the additive partial vectors in the desired direction.

Randall Parker said at June 15, 2009 6:25 PM:

Nick G,

An asteroid directly ahead in the same orbit of us shooting ions back at us in order to accelerate itself would tend to bombard us with ions that would slow us down.

The asteroid needs to be in an orbit where its ion propulsion wouldn't hit us I think. But if it is at a higher radius orbit it will orbit at a slower rate. We need something that is a little out and in front of us. How to do that?

Billy Oblivion,

Why make life hard on ourselves?

Engineer-Poet said at June 16, 2009 6:59 PM:

I don't see nitrogen burial working, naturally or otherwise.  The biosphere has been remarkably successful at burying carbon at times, but if there were nitrate flats in history we would never have heard the name Haber-Bosch.

Neither are you going to decrease the rate of fusion of the Sun.  The Sun's core contracts until pressure from fusion heating offsets gravitational forces.  The accumulation of denser helium requires hotter temperatures to offset the increased gravity.  About the only thing you could do is bombard the core with high-energy neutrinos to convert helium back to hydrogen; if you've got the ability to do that, you don't need a star in the first place.

Moving the planet is possible.  You don't need to do it continuously, you can do it via many gravity-sling maneuvers with one or several objects of relatively small mass.  The tradeoff is that both energy and angular momentum are conserved, so you have to move one or more bodies inward and balance the system somehow.  I would suggest moving Earth out, Mars in (both to supply the angular momentum and to make it habitable), and using Venus and/or Mercury as the energy supply.  The end state would be Mars at one of Earth's trojan points.

Last, why move a planet when lesser measures will do?  A large orbiting band of powersats in and around the ecliptic will provide both shade and oodles of energy.  You just tweak the orbital planes so that they reach maximum coverage on the Earth-Sun axis.

Nigel said at June 23, 2009 5:34 AM:

What is probably of greater concern to us is that the the gas layer that surrounds the earth (the atmosphere) must surely be evaporating into space. This would effectively cause the earth atmosphere to get thinner and thinner over thousands of years. Has anybody done any scientific studies to prove that the mean atmospheric pressure has been constant over an extended period of time? My hypothesis is that, given all the secondary (man-made causes) causes of global warming, we are up against a much stronger natural force that is stripping the earth bit by bit of it's precious atmosphere. The thinner the atmosphere becomes the more hostile the environment we have to live in! Are there any scientists who have pursued this line of thought with verifiable statistics yet? I would love to know.

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