Could fixing the climate impact stargazing?

Gernot Wagner of New York University explains how volcanoes could provide inspiration for a climate-change solution, and considers with the help of the University of Cambridge's Matthew Bothwell whether this could lead to unintended consequences...

Gernot - Maybe - we should probably take this outside.

Chris - No, don't do that. We need to record this programme.

Gernot - But just to be clear, that might be one of the smallest possible impacts or risks of solar geoengineering. I mean, it might change how the sky looks ever so imperceptibly.

Chris - Did you want to tell us actually what you would do then? Say you wanted to cool the planet, to do it quick and do it safely, what would you put and where?

Gernot - Here's what volcanoes do: in 1991 Mount Pinatubo erupts in the Philippines and in 1992 global average temperatures are about a half a degree centigrade cooler than they would have been without that volcanic eruption. If you throw tiny reflective particles into the stratosphere, into the lower stratosphere, somewhere around the equator, those reflective particles within weeks spread around the Earth and for a few months, for a year, maybe a year and a half, reflect sunlight back into space.

Chris - But what are those particles? Because obviously volcanoes are chucking out sulphur. For example, you could then get acid rain, couldn't you? Then obviously you're robbing Peter to pay Paul, because you'll have a cooler planet, but then you'll have dissolved everything on the ground. How are we going to do this safely then?

Gernot - It is sulphate aerosols - often that's the most prominent example. Now you don't get acid rain for the simple reason that up in the stratosphere there are no clouds. So as many problems as they are with solar geoengineering, acidifying the oceans of the world even further than we already do... Just to be clear, we do a lot of that by adding CO2 to the atmosphere, and that's a real problem. And, no, solar geoengineering does not address that root cause. But yes, there are lots and lots of unknowns, lots and lots of uncertainties. And frankly, the name of the game here is that we should be doing the research, right? Nobody sensible is calling for actually deploying any of this. And now we shouldn't, what we should be doing is figuring out whether it could work where the benefits as far as they are - and there are great benefits here, e.g. lowering global average temperatures - whether they do outweigh the costs, the risks, the uncertainties.

Chris - Have astronomers not got quite crafty ways of subtracting wonkiness in the atmosphere? So when light comes through the atmosphere, it causes stars to twinkle - the stars look like they're twinkling because light is bending anyway as it comes through the atmosphere. Have you not got clever adaptive ways of getting around this?

Matthew - Yeah, we absolutely do. Astronomers use the slightly stupid word 'seeing' to refer to this kind of twinkly bendy thing that light does when it comes through our atmosphere. And yes, we do have clever ways of dealing with it. Basically what we'd have to do is just make a model of the atmosphere - we live under a hundred miles of turbulent, wet gas - and if we can understand what the turbulence is doing, then we can subtract that out and see clearly. A lot of the issue we have with things going into space is not so much about the bendy twistyness of light as it goes through the atmosphere, but just particular wavelengths being blocked or even overwhelmed. The Starlink project, so Elon Musk's plan to put a bunch of satellites in space and broadcast internet around the world - that could be catastrophic for radio astronomy. Because with those things it's like putting a bunch of mobile phones or internet routers in orbit. Any radio telescopes on Earth might just be absolutely bombarded by these signals from outer space. If it's for a good cause, it might be hard to say no. The night sky is very wonderful and obviously astronomy is important, but if it's a choice between that and fighting climate change, I think I know what side I'd be on.