The principle of beneficence may be just as difficult to follow. Under the Belmont guidelines, doctors must balance the particular risks of a clinical trial with the potential benefit to any individual who might participate. Since it would be impossible to make such a calculation for every person on Earth, planet-hackers could at best choose the experiments that minimize harm to the most vulnerable communities—like people living on the coasts of Southeast Asia. But we may not know enough about the risks of geoengineering to make any such credible calculation when the time comes. Consider the Pinatubo Option, by which scientists would mimic the cooling effect of volcanoes. Putting particles in the stratosphere could reduce the total amount of energy that strikes the Earth. Some climate modelers say this would disrupt rainfall by reducing moisture in the atmosphere obtained by evaporation. Others say that geoengineering droughts and famines would be less harmful than those caused by unchecked warming. Right now, no one can agree on the nature of the risks, let alone the degree to which they would apply to particular communities.
And what about justice? Among the disruptions that could result from testing the Pinatubo Option is a weakening of the Asian monsoon, a source of water for hundreds of millions of people in India. Those in developing countries will "eat the risk" of geoengineering trials, shouted one of the climate scientists at Asilomar during his presentation. If representatives from just a small set of countries were appointed as doctors to the planet, then the less powerful nations might end up as the world's guinea pigs. Of course, the citizens of those nations also would seem to have the most to lose from uninterrupted global warming. These two dangers would have to be measured one against the other—and compensation as part of the experimental program could be one way of making tests more fair.
If medical ethics aren't quite up to the task of guiding our forays into geoengineering, what other sort of principles should we keep in mind? One important danger to be aware of is the moral hazard that might come with successful trials. That's the idea that protective circumstances or actions can encourage people to take undue risks—government insurance of banks led to risky investments that caused the savings-and-loan crisis in the 1980s, for example. Moral hazard looms particularly large for geoengineering studies since medium-scale field tests could prematurely give us the sense that we have a low-cost technical fix for global warming, no emissions cuts needed. (Moral hazard isn't quite as potent in medical research. The availability of cholesterol-lowering drugs may well discourage people from maintaining healthy diets, but it's unlikely that mere clinical trials would have the same effect.)
Another ethical principle that might apply to geoengineering is minimization—the idea that, a priori, it's better to tinker at the smallest-possible scale necessary to answer vital scientific questions. This notion comes from the ethics of animal experimentation; now we might apply it to planetary systems and the environment more broadly. Up until now, the medical ethics frame for geoengineering has guided discussions of how geoengineering might affect people in various countries. Perhaps we should be talking about how it affects the planet itself.
By that token, we might gain something by thinking of the Earth as a patient on its own terms. The rules and regulations we come up with for tests of geoengineering should take into account the way those experiments might affect ecosystems and nonhuman animals, both under threat from warming. And so maybe the most famous piece of medical ethics ought to apply: the Hippocratic Oath. "First, do no harm" is the crux of the original, but an updated version exhorts doctors to avoid "the twin traps of overtreatment and therapeutic nihilism." The climate crisis may force us to act despite myriad ethical challenges, for our benefit and for the planet's.