Rapids

The Paris climate agreement’s goal of stopping the world warming more than 1.5 °C produced a strong but mixed response from scientists. While most welcomed its intention, and the marker it put down, some, including me, were also alarmed, wondering how that goal might be achieved. Here’s the truth, made all the more plain by the possible withdrawal of the US from the Paris agreement: if we wish to stay below 1.5 °C we have to deliberately intervene in the global climate system on a massive scale. Nothing of that scope has ever been attempted. The worst implications of a warmer world – sea-level rise, crop failure and population displacement – would make it immoral not to act if we can. These potential impacts look much less far-fetched than they did even a decade ago. We are nearing the point at which we must act. Hence the growing call for a full and frank discussion of all geoengineering methods. These would aim to alter the planet’s radiation budget, for example, by pumping reflective or cloud-altering particles into the air. In particular, field trials of radiation management (RM) methods to cool the Earth now need immediate support.

Why the urgency? Because we are in a raft without paddles heading towards a waterfall and we’re running out of options. We could paddle for the bank with our hands. That’s like curbing carbon emissions and requires co-operation and leadership. But we’ve left it too late – we’re too near the waterfall to make it to safety this way. We could build makeshift paddles to row quicker. This is like greenhouse gas removal, the development of technologies that suck carbon dioxide out of the air – so-called negative emissions. But it looks doubtful we can make the paddles in time. Or we could brace ourselves for the inevitable, strap ourselves in and those that have them might put on hard hats in the hope they are sufficient. This is adaptation, like bolstering coastal defences or relocating threatened populations and letting the waters rise.Alternatively, we could swim for it. But that’s risky as the water looks cold and not everyone can swim. This is like using radiation management. You can do this quickly and relatively cheaply but the outcome is less certain. This option, given its potential for rapid deployment, has been woefully under-researched.

The waterfall analogy highlights the importance of information. If we knew how long we have before we fall over the waterfall, the severity of the fall, the amount of time it would take to make a paddle and the temperature and depth of the water you could make a more informed decision. More geoengineering research will give us more information. Fortunately, these options are not mutually exclusive. In reality, climate change is unlikely to have a single catastrophic point of failure, and might, to stretch the analogy, be a series of increasingly severe drops. Of course it makes sense to properly explore all options – continue to wean ourselves off carbon, develop negative emissions technologies and brace for the impacts of climate change. But we must also “test the water” in case we decide to swim for it. That means considering properly, through research and a more open and honest discussion, the unpalatable choice of climate engineering through radiation management.