How much faith can we have in backup plans for the climate?

At 10:38 on a June morning in 1991, a volcano in the Philippines exploded.

Mount Pinatubo sent an ash cloud 35 kilometers into the heavens, killing hundreds of people and impacting millions more. Before the dust had fully settled, something else happened: Earth’s surface measurably cooled for a couple of years.

Last September, researchers in the UK lofted a balloon filled with sulfur dioxide, a common ingredient in volcanic eruptions, nearly 25 kilometers into the air before it burst. The no-frills experiment was described as a possible scientific first in the field of “solar geoengineering” – the scattering of particles into the atmosphere to deflect the sun’s rays, and create a cooling effect similar to Mount Pinatubo’s aftermath.

It likely won’t be the last test of the potential for solar geoengineering to help mitigate the climate crisis, even as it’s being likened to a scientific act of desperation.

A group of experts published an open letter last month pressing for more rigorous and responsible study of solar geoengineering, “as rapidly as possible.” That followed a 2021 report issued by the National Academy of Sciences in the US, calling for an international registry of related research that asks “not just can we, but should we?”

There’s inevitable tension involved in tinkering with the weather in one part of the world in ways that may negatively impact another, potentially drawing a response. Or in a pursuit that could just end up making a bad climate situation worse. That means even as models suggest solar geoengineering could help prop up food production in a warming world, skepticism abounds.

Mexico recently announced plans to ban solar geoengineering experiments. A global initiative was formed last year solely to halt its development.

Momentum behind the concept grows, however, the more challenging it seems to limit warming to a point where it can prevent increasingly catastrophic impacts.

Experts have warned that exceeding 1.5°C in warming above pre-industrial levels would increase risks related to health, food security, and water supply. Warming reached an estimated 1.21°C as of January; it’s been projected to hit 1.5°C by 2035.

Yet, giving up on the 1.5°C goal and focusing instead on ways to soften the climate blow, like solar geoengineering, could be a grave mistake.

That hasn’t stopped people from conjuring up other varieties of backup plan.

One proposal would use thin-film space bubbles floating above the planet to deflect sunlight. Another is based on the idea that dumping iron into the ocean will help spawn carbon dioxide-devouring phytoplankton. Last month, astrophysicists suggested firing plumes of dust from the moon’s surface to create a “solar shield” for Earth.

It may be controversial, but solar geoengineering is also an inevitable part of discussions about what should come next after years of climate inaction.

One solar geoengineering research effort at Harvard University aims to launch a balloon from a platform in Sweden 20 kilometers into the sky, to release mineral dust and measure the resulting atmospheric chemistry and light scattering. It’s drawn significant pushback, and in 2021 the test was suspended pending a “more thorough societal engagement process.”

The UK government said it has commissioned studies on the effects of solar geoengineering, but has no plans to deploy it. The German government has funded related research, and China has reportedly assembled one of the biggest research programs in the world. Last year, the US government moved ahead with its own effort.

Uncertainty about who should own the intellectual property underpinning a potentially world-saving science is yet another source of friction. Actively involving the developing economies most vulnerable to climate change in discussions about how solar geoengineering is (or is not) developed is also a point of concern.

There are technical matters to be sorted out, too.

Questions have been raised about how to best get the necessary particles into the air, for example, and how high they need to go in order to be harmless and effective.

If particles really have to be released at an altitude roughly double that of typical flight paths for airliners and military jets, that could point to serious cost and safety hurdles.

Measuring the effectiveness of solar geoengineering may also be less than straightforward.

Perhaps the biggest hang-up to date: “termination shock.” If countries do manage to collectively ramp up solar geoengineering efforts, experts say, an abrupt interruption due to a war, for example, or even a shift in political will within a particular country, could trigger a calamitous spike in pent-up warming.

The science fiction author Neal Stephenson, known for portrayals of a post-apocalyptic future, made the title of his most recent book a reference to the concept.

All of this means that an extraordinary degree of international cooperation would be required to safely make solar geoengineering work. Among the many issues with the proposed technique, this seems to fall under the category of addressable problem.

Any discussions about its further development can and should be as global, inclusive, and transparent as possible.

That would count as a win, regardless of whether solar geoengineering ever becomes a reality or not.

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