By Kate Marvel

When an oxygen tank exploded on the Apollo 13 spacecraft, its three astronauts had to move to a smaller module designed to support only two of them. After the move, the crew breathed a sigh of relief -- a dangerous thing to do. With each exhale, carbon dioxide levels rose a little more, and it soon became urgent to remove all that human-emitted carbon dioxide from the ship's atmosphere. Using tube socks and duct tape, the crew fashioned a makeshift filtration system, ultimately landing safely back on Earth. In a true emergency, you throw everything you have at the problem.

Today, excess carbon dioxide in the air is causing problems for all of Earth. To prevent the worst-case climate scenarios, it's obvious that we need to drastically cut our emissions of carbon dioxide. But achieving this goal will require massive effort and sustained social and political change. So while we're at it, it makes sense to come up with a Plan B -- tube socks, duct tape and all.

That Plan B is "geoengineering": deliberately manipulating our planet's atmosphere and climate. The idea sounds like hubris, and most scientists worry that even talking about hacking the climate is dangerous. At best it would be expensive and only partially effective; it could also have unpredictable consequences, potentially even catastrophic ones. There is also the question of moral hazard: If temperatures can be lowered and carbon dioxide removed through artificial means, will we just emit more of it?

But the fact is that human beings have remade the world already. We now use half of Earth's ice-free land for farming; the total mass of manufactured plastic is about twice the mass of all animals put together. We've changed the chemical composition of the atmosphere, increasing carbon dioxide concentrations by almost 50%. All of that was done inadvertently, the result of population growth and technological progress. Now we could change the planet on purpose.

The most obvious way to hack the climate is to "turn down" the heat of the sun by reducing the amount of solar radiation that reaches Earth. Certain large volcanic eruptions naturally cool the planet by spraying particles into the stratosphere, where they block sunlight. It would be both feasible and relatively cheap to do the same thing by releasing sulfates or minerals in aerosol from a fleet of jets.

Another approach would be to hack the carbon cycle. Like the Apollo 13 crew, we might be able to remove carbon dioxide from the air to make ourselves safer. Trees do this already, but when they are cut down, burned, or die naturally, the carbon they've stored is returned to the atmosphere. The challenge is that adding enough new trees to make a dent in global carbon emissions would require an enormous amount of land: To offset emissions from the U.S. alone, we'd need to plant more than 600 trees per person every year.

"Direct air capture" $(DAC)$ technology can accelerate the process by pulling carbon out of the air, but for now it is expensive and uses substantial amounts of energy. A large DAC plant might be able to remove one million tons of carbon dioxide from the atmosphere in a year. Human beings currently emit that much every 13 minutes.

A third climate hack involves turning to the ocean for help. Earth's oceans are becoming more acidic as carbon emissions increase, because carbon dioxide reacts with seawater to form carbonic acid. Dumping an "antacid" of rock dust into the oceans would reverse this process, causing the water restore its natural balance by absorbing more carbon dioxide from the air. Electricity could also drive chemical reactions to remove carbon dioxide from seawater, forcing it to take up more from the atmosphere. And we could encourage more living things to grow in the seas, especially plants and phytoplankton that extract carbon dioxide from the atmosphere through photosynthesis.

Finally, we could turn to the ground beneath our feet. As rocks are worn away over millions of years, they release elements like calcium, which interacts with the carbonic acid in rain to form limestone. Once carbon is removed from the atmosphere by this sluggish process, known as rock weathering, it stays put for a hundred million years.

"Enhanced" weathering speeds up this process by grinding rock into dust and scattering it over the Earth's surface, thereby increasing the area exposed to the elements. This method has the advantage of being simple and powerful. We may be able to remove a billion tons of carbon dioxide from the atmosphere every year simply by scattering rock dust on farmers' fields. Some arable lands might actually benefit from a sprinkling of the right sort of rock dust. It takes a lot of energy to grind rock into dust, but mining has already created a large amount of pulverized rock that could be repurposed for carbon removal.

All of these methods have the potential to help, if deployed correctly. The problem is that none has been attempted on a large scale, so no one knows for sure what the impacts might be. Spraying aerosols into the atmosphere could change global rainfall patterns or damage the ozone layer. Farming seaweed or phytoplankton at the levels required could displace other uses of the ocean, like fishing, shipping, and offshore wind power generation. Changing the chemistry of the ocean could disturb or destroy the ecosystems that sustain other animals and plants.

With so much at stake, cooling the planet should be a decision made by all of humanity. Unfortunately, there is no institution capable of marshaling global consensus. And it's too late to take these ideas off the table. Billions of dollars are already pouring into carbon removal; governments are funding research into climate modification.

Climate scientists may disagree on whether we should block the sun or hack the carbon cycle. But there is broad consensus that the best solution to climate change is Plan A: reducing greenhouse gas emissions as much as possible, as quickly as we can. As Apollo 13 showed, we are a species smart enough to send people to space and resourceful enough to rescue them when things go wrong. We may be capable of cleaning up the mess -- but only if we stop making it in the first place.

Kate Marvel is a climate scientist. This essay is adapted from her new book, "Human Nature: Nine Ways to Feel About Our Changing Planet," which will be published June 17 by Ecco.

(END) Dow Jones Newswires

June 12, 2025 11:08 ET (15:08 GMT)

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