Could we refreeze the poles to fight climate change?

We’re going to examine some of the more leftfield attempts to tackle climate change. Shaun Fitzgerald from the University of Cambridge's Centre for Climate Repair is doing just that...

Shaun - Every scenario considered by the IPCC in their most recent report considers a large suite of measures on emissions reduction complemented by greenhouse gas removal. And while some of those actually do see us below 1.5 degrees Centigrade by the end of the century, the sad fact is that every scenario that they now consider sees us exceeding one 1.5 Degrees Centigrade in the interim period. And we're greatly concerned about the changes which are going to be unleashed on the planet. In other words, the loss of ice on Greenland, the loss of ice on Antarctica. And therefore what we're trying to do is equip ourselves with knowledge so that a society can make an informed decision as to whether these engineering solutions could be put in place in order to buy us more time to get greenhouse gas levels down whilst keeping the ice on Antarctica and the ice on Greenland, for example.

Chris - In a nutshell, are you basically advocating for refreezing Greenland?

Shaun - Well, I'm certainly advocating for doing everything that we can to keep the ice on Greenland and the ice on Antarctica.

Chris - Greenland has lost billions of tonnes of water provoking some of the sea level rise that you've just been referring to. So this is not a small trivial thing to just keep the ice there. How do you anticipate trying to do this?

Shaun - In general terms, there are two big factors that determine the temperature of the Earth and therefore the rate of, for example, melting of ice on Greenland. The first is the amount of radiation coming in from the sun. And what we can do is look at measures to reduce the amount of the sun's radiation that actually gets down to the Earth's surface. And those approaches are termed 'solar radiation modification.' They can include things, for example, by emulating the effects of volcanoes. Volcanoes such as Mount Pinatubo, when it erupted, spewed about 20 million tonnes of sulphur dioxide into the stratosphere that then reacted with water vapour to form little droplets of sulphuric acid. And those little droplets of sulphuric acid were at the right length scale diameter that they were able to reflect a very small portion of the sun's radiation. And the second big idea is whether you can actually get more of the Earth to radiate heat out at night and actually help therefore, in terms of the overall radiation balance, over either a year or certainly over a day.

Chris - Let's start with the first of those ideas. You've presumably done more than just back of the envelope calculations on what this is going to take. So hit me with the hard facts. How much cloud forcing or seeding have we got to do in order to preserve the Arctic?

Shaun - Something like 10 million tonnes per year of sulphur dioxide being injected into the stratosphere could indeed cool the Earth by circa one degree Kelvin. And that's a really useful benchmark. Now what does that really look like? In other words, how would you get 10 million tonnes of sulphur dioxide up into the stratosphere from an engineering deliverability point of view, that's thousands of flights of aircraft a day in order to get to that sort of kind of delivery schedule.

Chris - The other idea you proposed was to try to get the Earth to get rid of more heat. Tell us a bit more about that because I haven't heard anyone say anything about that.

Shaun - Well, one of the things that we are looking at is something called sea ice thickening. The first effect of this is that how can you get more sea ice to grow in the Arctic winter? And the reason why you might want to do that and get the ice to be thicker is that the ice will actually then last longer over the Arctic summer and therefore reflect more of the sun's radiation as it impacts on that ice in the Arctic summer. But let's just think about what's going on in the Arctic winter. What you are really doing is if you are getting more ice to form in the Arctic winter given there's more freezing, then the latent heat of solidification has got to go somewhere. And ultimately what you're doing then is actually getting that latent heat of solidification freezing to be radiated out to space in the arctic winter. And the way that you do that potentially is by pumping sea water, not very far, but pumping it up from under the ice to on top of the ice and getting the freezing process to then occur on top of the ice. The top surface of the ice in the winter is, let's say, -20 degrees centigrade. If you've pumped the water on top of the surface, then by definition it's liquid water and the temperature is no longer -20 degrees centigrade. The temperature is let's say -1.5 degrees centigrade. But that difference in temperature actually results in an increase in the rate at which heat is being radiated out to space in the Arctic winter.

Chris - And how much energy have we got to expend pumping water in order to get a net cooling effect?

Shaun - There are two flavours of this particular problem that we are looking at. The first is where you are pumping sea water on top of the sea ice in order to make that new sea ice on top of existing sea ice. The second idea that we are looking at is where, in fact, all you are doing is pumping enough water on top of the sea ice to consolidate any snow that then falls naturally on the sea ice. And if you can turn that snow into solid ice, snow is a ridiculously good insulator and therefore you've increased the conductivity of the overall matrix. And what that means is that just pumping enough water to convert the snow into solid ice, you've increased the rate at which new sea ice can form naturally. And you know, that will require far less pumping, far less energy for a given amount of new sea ice that can accumulate naturally. That one excites me greatly. But we are looking at both of these approaches, Chris.

Chris - How does this go down when you present these ideas both at home, but also when you go to conferences or international meetings and so on, and you talk to the community about these ideas? How does this go down with fellow engineers, climate scientists, et cetera?

Shaun - I get a mixed response to be quite straight with you. Those who have an open mind as to say 'look, we're not in a good place, but we need to be learning more so that society can make more informed decisions', are really eager to help. Whereas there are those who think these sorts of ideas are a distraction. And whilst I accept that that is a viewpoint, I don't agree that that is the cause of the lack of progress that we have made on emissions reduction to date. When we go and talk to people about why we've been making such poultry progress on emissions reduction, it's very, very rare that I hear, in fact I've never heard the argument being that it's because climate engineering is going to get us out of this hole. We need to make much more progress on emissions reduction. And emissions reduction is necessary but not sufficient in my view.