Limiting the rise in global temperature to less than 2°C over the preindustrial baseline is the defining challenge of our times. Anything beyond that threshold would set in motion runaway feedback loops. For instance, some of the Arctic would melt. With no ice to reflect the sun, the sea would heat up. This, in turn, would melt more ice. And so on.

The scientific assessment of this scenario is “catastrophic”.

We’re in this crisis because we burn fossil fuels, have cut down the majority of our forests, and raise billions of farm animals each year. Each of these activities releases greenhouse gases, such as CO2, that prevent heat from radiating back into space.

What we have to do, then, is to try to limit any additional greenhouse gas emissions. But that’s hardly going to be enough, given that we’ve already emitted so much. So we also need to remove greenhouse gases from the atmosphere. That’s what the IPCC report means when it recommends “negative emissions”.

The renewed interest in carbon capture and geoengineering is, in other words, a reaction to our failure to reduce emissions. But is geoengineering really necessary? Is carbon capture safe? Are these technologies an experimental drug for a dying patient, or should we vote for politicians who promise to implement them?

The truth, as usual, is complicated. Not all carbon capture and geoengineering techniques are equal. Some show real promise, while others carry enormous risks to life on Earth.

What is geoengineering?



Geoengineering (sometimes called climate engineering) is a large-scale, intentional and tech-driven manipulation of the environment. The idea has been around for a while – John F. Kennedy referred to it as “weather control” in the sixties. Many people think of geoengineering as the “Plan B” for our planet – "the morning after pill for societies that do not practice safe consumption."

Governments around the world are now giving serious thought to geoengineering. The US, the UK, and China – among others – are heavily investing in research programmes.

How does geoengineering work?



Geoengineering aims to reduce temperature. Most geoengineering methods do so by blocking out the sun in one way or another.

Some of these methods are low-tech. Back in the 60s, American researchers suggested floating white objects on the ocean to reflect sunlight.

Most geoengineering methods, however, would require untested (and largely unavailable) technologies, e.g. launching space shields that block out solar radiation, or refreezing parts of the ocean by injecting salt particles into polar clouds, which would make them brighter and more reflective.

The most widely discussed geoengineering method consists in injecting reflective aerosols into the atmosphere. Here’s how that would work: a fleet of high-altitude planes would fly around the world and spray sulphate into the stratosphere. The number of flights would gradually increase, eventually amounting to 60,000 flights per year. This technique aims to mimic volcanic eruptions, which are known to reduce global temperature.

How safe is geoengineering?



It’s easy to get excited about geoengineering. But most geoengineering technologies carry substantial risks.

Consider the injection of reflective aerosols. Since most sulphate particles would only stay aloft for a couple of years, we’d have to keep injecting them indefinitely. And unless we stop emitting greenhouse gases, we’d have to inject ever greater quantities. If the geoengineering program got cancelled, global warming would return with a vengeance.

It’s unclear whether humanity is capable of sustaining a coordinated, international effort for hundreds of years. We haven’t had the political stability to do so in the past.

Reflective aerosols would also have many unintended side effects. They might bring down global temperature, but they’d also endanger the ozone layer. And they’d risk disrupting regional weather patterns, such as the Indian monsoon. This would be disastrous for the millions of farmers who depend on it.

Finally, aerosol injections would only target one aspect of the climate crisis, i.e. temperature. Other problems, such as ocean acidification, would remain.

In short, geoengineering techniques aren’t magic bullets. And they also increase the risk of conflict. Changing the climate is to yield significant power on a global scale. Who would control geoengineering, and who would fund it? How would decisions about geoengineering be made? Would poor countries be consulted?

Pinning our hopes on geoengineering could also distract us from the hard but necessary work of reducing emissions. We’ve been talking about geoengineering since the sixties, but we still don’t have a technology that would be safe to deploy on a large scale. Let’s face it: it’s getting a bit late for future technologies.

What is carbon capture?



CO2 emissions are the driving cause of climate change, so removing the gas from the atmosphere is an effective countermeasure. There are two ways this can (theoretically) be done.

The most intuitive method is to capture carbon from the air, and then store it (in underground saline aquifers). Most research focuses on doing this at fossil fuel energy plants, since the majority of CO2 is emitted there. Some direct-air-­capture startups are also developing products that would have wider uses. This technology is still in its infancy, however.

The second method is to fertilize the oceans with iron. This would stimulate the growth of algae that already absorb a lot of carbon. The oceans would consequently absorb more carbon from the atmosphere. At least that’s the theory.

How safe is carbon capture?



Capturing carbon from the air is generally considered to be safe, but the technology doesn’t exist yet. The main risk of direct-air-capture technology is that it won’t be developed in time.

Fertilizing the oceans with iron is more risky than direct-air-capture. The increase in algae could disturb the marine ecosystem, and phytoplankton bloom could produce toxins. Some scientists even doubt whether local CO2 absorption can increase the ocean’s overall carbon uptake at all.

As with geoengineering, it’s important not to think of carbon capture tech as a magic bullet for all our climate problems. At best, they will be a part of the puzzle.

How to mitigate climate change



One way to go forward would be to develop geoengineering, but only to deploy it as a last resort. It would, however, be difficult to tell when exactly that would be. Who would declare the emergency? Another difficulty is that the line between research and implementation tends to fade over time. A better way to go, therefore, is to research only the most promising technologies, such as direct-air-­capture.

In addition to that, we should use the technologies that are already available. Trees are a natural carbon capture technology: they capture and store carbon from the air. And trees are not only safe, but have many additional benefits. Diverse, native forests – the kind Ecosia plants – increase soil fertility and restores the water cycle, for instance.

Finally, we have to face the fact that there’s no way around reducing greenhouse gas emissions. This might be uncomfortable – saving the world often is. But it won’t be painful. Not if we remind ourselves what really matters. Whatever that might be for you, it’s probably not fossil fuels.