Geoengineering as climate change plan B

Clearly, the best way to address climate change caused by greenhouse gas emissions is to stop emitting greenhouse gases. Which is great, except we don’t seem to be very good at that – particularly in terms of getting international cooperation.

So what do we do if it turns out we can’t cut emissions quickly enough to avoid catastrophe? Or to put it another way, science and technology kind of got us into this mess, so can it get us out of it?

Satellite image of fires and deforestation on the Amazon frontier, Rondonia, Brazil (click to see more)
Satellite image of fires and deforestation on the Amazon frontier, Rondonia, Brazil, on 12 August 2007. Intact forest is deep green, while cleared areas are tan or light green. Clearing forest like this releases a great amount of carbon dioxide and removes a valuable carbon sink, so why not try and reverse the process? (By Jesse Allen and Robert Simmon of NASA Earth Observatory, via Wikimedia Commons)
What we’re talking about is geoengineering. It may sound far-fetched, or perhaps like a super villain plot, but it’s being given considerable thought by seriously serious bodies like Intergovernmental Panel on Climate Change (IPCC) Expert Meetings and, more locally, a Pilot Workshop on Asian perspectives.

But what exactly is geoengineering? Well, the options analysed in an influential 2009 paper by the UK Royal Society can be split into two categories: carbon dioxide removal and solar radiation management.

In the list below, we rate these options by their predicted effectiveness and craziness – the inverse of the Royal Society’s assessment of affordability, timeliness and safety.

Carbon dioxide removal

The least crazy options involve removing the primary cause of climate change, which is carbon dioxide (CO2) in the atmosphere. Many of them are good ideas anyway, but they also tend to be the least effective.

land use management, afforestation, reforestation and avoidance of deforestation

Trees are clearly good at using up atmospheric carbon dioxide, so replanting forests or ceasing to chop them down makes a lot of sense. And then there’s afforestation, which is planting trees where there weren’t forests before. These actions are pretty popular, and it’s usually what people are talking about with carbon offsets. But the problem is that it’s pretty slow to take effect compared to the rate at which we’re emitting. Craziness: low. Effectiveness: also low.

bio-energy with carbon sequestration

If we’re going to grow more plants to consume CO2, then why not burn the resulting biomass in place of fossil fuels? And better still, when we burn it, why not bury the carbon it releases (sequestration) instead of emitting it into the atmosphere? Sounds good, but its potential is limited because it would have to compete for land with food growing, which we’re already struggling with. Craziness: medium. Effectiveness: medium to low.


This is basically the same concept as bio-energy, except instead of burning the biomass we just bury it all – which actually makes it more expensive than bio-energy. And then there’s the question of where you bury it and what happens after it’s in the ground. Craziness: medium to high. Effectiveness: low.

enhanced weathering

Just for something different, certain rocks chemically react with and dissolve CO2. This takes place naturally over thousands of years, but maybe we can speed it up – i.e., enhance weathering – by spreading silicate or carbonate rocks over the ground or the ocean. The only problems are that it’s rather expensive, and is likely to have adverse effects on the environment where it’s released. Craziness: medium. Effectiveness: high.

carbon dioxide capture from ambient air

We’ve already developed artificial mechanisms for removing CO2 from industrial exhaust, or from air supplies in submarines, so why not use the same techniques for pulling it out of the atmosphere? Well, it’ll take a while to develop something that works on that scale, and it’s likely to require quite a bit of energy. But if we can use renewable energy, then it might just be feasible. Craziness: medium. Effectiveness: high.

ocean fertilisation

This is something we’ve considered before on Lost in Science: using iron to encourage plankton growth. It’s pretty simple to do, but trials have shown that it’s not as effective as you’d think. Plus, it changes the marine ecosystem, and if we’ve learned anything about changing the environment, it’s that it’s rarely a good thing. Craziness: high. Effectiveness: low.

ocean upwelling or downwelling modification

CO2 naturally cycles from the atmosphere into the ocean depths. Can we speed up that process? Most likely, no. Craziness: extreme. Effectiveness: negligible.

Satellite image of the plume from the eruption of the Puyehue-Cordón Caulle volcano, Chile (click to embiggen)
Satellite image of the eruption of the Puyehue-Cordón Caulle volcano, Chile, showing just how much material it releases into the atmosphere. Volcanic plumes like this have a noticeable cooling effect on Earth's climate, so could we do something similar to reverse global warming? (By NASA Goddard/MODIS Rapid Response Team, via Wikimedia Commons)

Solar radiation management

Rather than trying to remove the cause of climate change, we could focus on the effects and find another way to reduce global temperatures, and the obvious way to do it is to block out the sun. Most of the techniques for doing that have considerable side effects, and don’t really affect the weather in the same way as reversing the greenhouse effect. They also don’t fix other problems caused by CO2, like ocean acidification.

solar albedo (brightening human settlements)

This involves painting roofs, roads and pavements white to reflect sunlight back into space, stopping it being absorbed and heating the Earth. But really, this can only be done on a very small portion of the Earth’s surface, so the effects are minimal and the costs are immense. Craziness: medium. Effectiveness: very low.

solar albedo (desert reflectors)

There is an interesting proposal to cover all the Earth’s deserts (about 2% of the surface area) with a reflective polyethelene-aluminium surface. Needless to say, this would also be very expensive and very damaging to desert ecosystems. Craziness: medium to high. Effectiveness: medium to low.

cloud albedo enhancement

White, fluffy clouds also reflect sunlight, and we can seed them to increase their whiteness and their fluffiness. Unfortunately, this is likely to effect the weather locally, i.e. where the clouds are, and cause unpredictable changes. And, depending on what you’re seeding the clouds with, you could also cause a new type of pollution. Craziness: medium to high. Effectiveness: medium to low.

stratospheric aerosols

This is actually a very well understood cooling mechanism, because it’s routinely done by volcanoes emitting sulphur particles. But although it’s effective, it has a number of undesirable side effects, like reduced precipitation (increasing drought particularly in Asia and Africa) and further damage to the ozone layer. Craziness: medium. Effectiveness: high.

space-based reflectors

So how about we get really serious and send a giant umbrella out into space to block the sun? It’s perhaps not quite as damaging to the environment as stratospheric aerosols, but it’s vastly more difficult and expensive. Craziness: high to very high. Effectiveness: curiously, also high.

Screenshot of Mr Burns blocking out the sun in The Simpsons
Montgomery Burns tried a similar technique in The Simpsons episode "Who shot Mr Burns?" As the title suggests, it wasn't a very popular move.

All the techniques on this list come with serious moral issues, on top of their substantial practical and environmental risks. Questions such as, who controls the use of geoengineering technologies? Will rich countries care about negative effects on poor countries?

Does it come across as a free ticket to keep emitting? Would it ever be safe to turn it off?

The risks are very high, so it’s tempting to say we shouldn’t even consider it. But again, if everything else fails we may need a plan B, so maybe we should research it just in case? Or even just so we know what the risks are?

Or is doing any research itself too dangerous, because it sets us down a path to using the technology?

These are political and moral questions that science alone cannot answer. This planet belongs to all of us, so we all need to weigh up the issues. What do you think?

Tell us your opinion in the comments below…


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