Can changing the Earth's orbit reverse the effects of climate change?
During a congressional hearing last week, Republican Representative Louie Gohmert of Texas asked a US Forest Service official if her organisation or the Bureau of Land Management could change the orbit of the moon or Earth to reverse the effects of human-caused climate change. Lets do it. First, we must take stock of what we havethe givens in what will be our equation for moving Earth. Our planet orbits the sun at an average distance of 149.6 million kilometres, and it soaks up enough sunlight to have an average temperature of about 15 degrees Celsius. The latter figure is, however, an increase of slightly more than one degree C from Earths typical temperature across the past century. In short, this world is running a low-grade fever. According to current consensus estimates, that fever is likely to get much worse if left unchecked, raising Earths average temperature by another one degree C by the 2060s. Such an increase would render some presently people-packed parts of the planet effectively uninhabitable and threaten the sustainability of global civilisation as we know it. Radiative equilibrium, the balance between incoming energy from the suns rays and energy emitted from Earth, is key to our understanding of our planets changing temperature, says Britt Scharringhausen, a planetary astronomer at Beloit College. It is described in the following equation, as scribbled out by Scharringhausen:  A page from Britt Scharringhausens lab notebook, showing a handwritten equation for determining a planets radiative equilibrium, which sets its effective temperature. Credit: Britt Scharringhausen  Here, Tp is Earths temperature, T is the suns temperature, R is the suns radius, D is the distance to the sun, and a is Earths albedo, or reflectivity. Albedo measures how well our planet reflects solar energy, where 0 would be perfect absorption and 1 would be perfect reflection. There is a connection between climate change and albedo: snow and ice, for instance, have a high albedo, reflecting up to 90 percent of the sunlight that hits them back to outer space. Anthropogenic warming causes snow and ice caps to melt, which can make Earths albedo decrease. That, in turn, eventually leads to a higher average planetary temperature. Some variables in this equation are changing naturally. Our star is very slowly swelling and brightening, becoming slightly larger and more luminous as it ages. Ethan Siegel, a theoretical astrophysicist and science writer, says that while it will take the sun on the order of 100 million years to increase in luminosity by 1 percent, our greenhouse-gas-emitting global civilisation is projected to increase the solar energy retained by Earth by 1 percent over the next few hundred to 1,000 years. Read | Irreversible global warming tipping point possibly triggered: Arctic mission chief  To make Earth cooler, we need to decrease a variable on the right side of the equation: We cant easily lower the suns temperature or radiusand clearly meaningful reductions to our heat-trapping, albedo-shifting greenhouse gas emissions are out of the question. So lets take Representative Gohmerts advice and simply increase D, the distance to the sun. All we have to do is find a way to move all 5.972 septillion kilograms of Earths mass farther away from our star. By Scharringhausens calculations, a three-degree-C decrease in temperature to counteract current and near-future anthropogenic warming would require us to move our planet an additional three million kilometers from the sun. Using another back-of-the-envelope calculation, Scharringhausen finds that 5 x 1031 joules could push all 5,972,000,000,000,000,000,000,000 kilograms of Earths mass three million kilometers out from its present orbit. These numbers present challenges for Representative Gohmerts plan, because annual global electricity production is around 1019 joules, or 0.0000000000002 percent of what wed need to move the globe. Thats also assuming we can apply all that energy to Earth at 100 percent efficiency, which, thanks to the laws of thermodynamics, is physically impossible. Setting aside such particulars, we havent addressed what form this applied energy would take. There is the literal nuclear option: one method that scientists have proposed to move an asteroid is to detonate a nuclear bomb near it, Scharringhausen says. It will basically vaporise part of the asteroid, and that escaping rock vapor acts like rocket exhaust and will push the asteroid along, she explains. Scaled up, such a mechanism could, in principle, provide enough oomph to shift a planets orbit. Still, it would take a billion times more nuclear explosions than we have ever set off to move Earth the required distance, or the equivalent of dropping an atomic bomb every second for 500 years, according to Geza Gyuk, director of astronomy at the Adler Planetarium in Chicago. The strategy of constantly detonating nuclear bombs near Earths surface with the goal of vaporising parts of it to act as rocket exhaust also has several drawbacks. For our purposes, the most notable deleterious effect is that the blasts themselves would heat up the planet, counteracting the stated goal of reversing global warming. A gentler option would be to siphon off the energy of other celestial objects, such as passing asteroids or comets, by engineering close planetary flybys. This technique is regularly used in reverse, with great success, by spacecraft that boost their speed by passing close to a planet to steal a portion of its orbital energy. For moving our planet, the issue with the method is scale, Siegel says: the total mass of the asteroid belt is only 4 to 5 percent of that of the moon, or 0.05 to 0.06 percent of that of Earth. Using the mass of the entire asteroid belt in flybys would migrate Earth away from the sun by less than 748,000 kilometers, or a quarter of the distance wed need, he says. And a single off-course collision with our planet would spark destruction approaching that caused by the asteroid impact that eradicated the dinosaurs in a global mass extinction. Fortunately, we have a much more massive space rock sitting in our backyard: the moon itself. Not in any way that were capable of doing today, Siegel says, and the consequences would be disastrous. Besides having greatly reduced tides, a moonless Earth would have much darker nights, shorter days and extreme, unpredictable seasons because of a destabilised axis of rotation. Increasing the radius of the moons orbit by 10 percent would affect Earths own trajectory around the sun in the long term, says Matteo Ceriotti, a rocket scientist at the University of Glasgows James Watt School of Engineering. We could extract and accelerate material off the moon, Ceriotti says. Using a 100-gigawatt laser, or one with about the power capacity of every single wind turbine in the U.S., it would take 300 trillion years to lift sufficient amounts of material from the lunar surface. There is always the aforementioned nuclear option, too, which could be used to move the moon rather than the Earth. Another, less messy choice would be to manually extract lunar material with conventional rockets. If we were able to build a spaceport on the moon and build a rocket equivalent to SpaceXs Falcon Heavy to lift off moon material into deep space, we would need 7 x 1016 launches, Ceriotti says. Thats 70,000 trillion rocket launches. For comparison, during the entirety of the space age, humankind has only managed to achieve 70,780 launches, and more than half of them did not leave Earths atmosphere. Humans could add a twist to the use of asteroids in the flyby idea and instead put them on a collision course with the moon, Gyuk says. We would need kilometer-sized comets to crash into the moon every second for a couple of hundred years to make a substantial difference. Again, though, an off-course projectile could cause a planetary mass extinction event. Because of the magnitude of the change necessary to increase the Earths orbit, any intervention would probably need to last for many millions of years at minimum, which raises an unexpected sociological issue, Gyuk says: We dont have precedent for planning across such vast timescales. And in fact, no civilisation in human history has endured more than a mere few thousand years. Finally, even if humans managed to alter our planets orbit using any of these methods, they wouldnt be able to rest easy, Siegel says. If we even somehow could make this enormous change in Earths orbit, he says, it doesnt absolve us from the responsibility that well keep needing to make this change as long as we keep increasing the greenhouse gas concentration in our atmosphere.  To my ears, that sounds like a stirring endorsement of our fossil-fuel-addicted status quo! We should immediately prioritise pouring all our energy into changing Earths orbit, starting now and lasting forever. Sure, its a Sisyphean task in which humanity is Sisyphus and the boulder being eternally pushed uphill is Earth itself. But at least wed get to keep driving our sweet SUVs! I say we get to work.