In “The Scientific Adventures of Baron Münchausen”, published in 1917, the baronial narrator sends an audience on Earth messages from Mars. There he has encountered vast cubes of wire mesh hung above the surface—the Martians’ air-purifying plants, scrubbing carbon dioxide from the atmosphere. It seems strange but, as the baron asks: “How long will it be, with your coal-burning machinery, till the Earth’s atmosphere will need cleaning plants?”
The answer, it seems, was a good bit more than one century, a good bit less than two. It looks highly likely that, despite progress in renewable energy, enough carbon dioxide will be emitted in the coming century to raise the Earth’s temperature more than 1.5°C above its pre-industrial level—and probably enough to push that increase beyond 2°C. The Paris agreement of 2015 says that is too much: countries of the world committed themselves to keeping warming to 1.5°C, if possible, and definitely to well below 2°C.
For this target to be met, climate models require that, well before the end of the century, humans become capable of taking back from the atmosphere billions of tonnes of the CO₂ they have put there. Technological interventions on such as scale are known as climate geoengineering. They are something policymakers have long shied away from, but now need to think about much more seriously.
Scaling up the Earth’s inbuilt mechanisms for removing carbon from the atmosphere (such as photosynthesis) can provide some of the “negative emissions” Paris requires. But the world cannot be entirely covered by forests. So it seems likely that, if humans do plump for negative-emissions geoengineering, at some point they will turn to technologies that can pull carbon dioxide directly from the air. In the past couple of years two companies—one Canadian, one Swiss—have built pilot plants. As yet they can produce only a few tonnes a day, rather than the few million tonnes that good climate management might eventually require.
Wishing carbon-sucking geoengineering into being to solve the paradox of Paris raises problems. As long as this capability remains necessary but vague, it becomes disturbingly easy to invoke as a way of deferring action. Policymakers need to acknowledge that they are relying on capabilities they do not yet know how to provide with side-effects they do not yet understand.
They also need to recognise the promise, and perils, of another form of geoengineering. This would seek to cool the planet by increasing the amount of sunlight it reflects back into space, which might be done by brightening particular sorts of cloud or injecting into the stratosphere a thin layer of particles similar to those seen after volcanic eruptions. In 2018 researchers from Harvard University intend to mount the first experiments in the stratosphere to investigate what the physical and chemical effects of a veil of particles might be.
These sunshine-geoengineering approaches are unique among responses to climate change in that they offer a prompt way to counter the effects of greenhouse gases already in the atmosphere. They could provide some immediate relief over the decades, or centuries, that emissions reductions (and negative emissions) would take to fix the underlying problem. They might also help to curtail peaks in temperature, which cause a disproportionate amount of the damage done by global warming.
Clouding the issue
The state of discussion about these sunshine-geoengineering technologies is almost the opposite of that about negative emissions. Because they have not been surreptitiously baked into policy, as negative emissions have, their possible benefits are underplayed; instead the focus is on the risks. If such an intervention were not designed properly, or did not behave as intended, it could make some people’s lives a lot worse rather than a bit better. This is particularly worrying because it could be done by a single country, or group of countries, in a way that benefited them in particular.
These risks have led some to call for a ban on ever deploying such technologies. But that would show a complacency towards the real risks posed by global warming. A better way forward would be to give the pros and cons of geoengineering a more explicit role in assessments, such as in the Intergovernmental Panel on Climate Change’s report on getting to a 1.5°C world, which will be published in 2018. They must also be included in policy discussions, such as the coming year’s “Facilitative Dialogue” on progress towards the Paris goals. At present, no one pays a price for leaving geoengineering out of discussions. That must change.
The Paris goals are unlikely to be met without some new approaches such as negative emissions. The best and fairest ways of meeting them might involve other novel approaches, too. But without a full and open discussion we may never know.