Engineering the climate

‘Man is unwittingly conducting a vast geophysical experiment. Within a few generations he is burning the fossil fuels that slowly accumulated in the earth over the past 500 million years,’ stated a 1965 scientific report to US president Lyndon Johnson. ‘The climatic changes that may be produced by the increased carbon dioxide content could be deleterious from the point of view of human beings,’ it went on. 

The wording is not too dissimilar to that of the latest round of scientific reports published in 2013–2014 by the Intergovernmental Panel on Climate Change (IPCC). The difference, nearly 50 years on, is the solutions proposed by the participating scientists. ‘In that [1965] report, the solutions that are suggested for climate change are what we would now call geoengineering,’ explains social scientist Steve Rayner who co-directs the Oxford geoengineering programme at the University of Oxford, UK. ‘There’s nothing in there about mitigating greenhouse gas emissions or even about adaptation.’

The 1965 report was largely ignored. Today, mitigation routes such as reducing emissions are the preferred (although not yet widely adopted) approach to tackling climate change. Adapting to the adverse effects of climate change – using flood defences for example – is the second choice, but very much complementary, approach. Geoengineering, also called climate engineering, remains a pie-in-the-sky idea with minimal research having been carried out into its viability so far.

Slow progress

It might seem surprising, given the alarming rate at which the globe is warming, that potential technical quick fixes for slashing temperatures haven’t been explored. ‘Even doing research into this topic has been considered very controversial from the beginning,’ explains Rayner. 

‘There are those who feel that it presents what insurers would call a moral hazard. This is the idea that if you reduce the possibility of harm, people then increase their propensity towards dangerous behaviour. The moral hazard, in this case, is the idea that if you even held out the possibility that there is a way of geoengineering our way out of climate change impacts, that this will reduce people’s impetus to engage in greenhouse gas emissions reduction activity,’ he says.

There are also worries that climate engineering, and even conducting small outdoor experiments to test the technology, could threaten global security. ‘If one country or group of countries were to engage in a geoengineering activity, that could cause international tensions with countries that are vehemently opposed to the activity or feel that they are being adversely affected,’ says Rayner.

‘The unfortunate thing about the way the Earth’s climate system works is that it is quite good at transmitting what happens locally to the rest of the globe, so it becomes very difficult to geoengineer regionally,’ explains Piers Forster, a climate scientist at the University of Leeds, UK. This means that even small-scale experiments will affect the whole planet. And although the effect is global, the computer modelling done so far suggests there would be strong geographical variations. This inevitably means some countries would be left better off than others by any climate engineering activities. ‘That will bring lots of ethical considerations about whether we should be doing it or not,’ says?Forster. 

This controversy has meant that minimal research has taken place into any of these technologies. It is therefore not yet known if any of them would have the desired cooling effect or if they would have intolerable side effects. In 2009, the Royal Society published a report calling for further research into climate engineering. The report recommended the UK government spend £10 million per year for 10 years on research in this field. In the five years since the report was published, less than £1 million per year has been spent in the UK, says Rayner. ‘We are not seeing sufficient investment to allow us to better understand if this is a smart idea or a silly one.’ 

Boosting clouds’ reflectivity

The climate engineering technologies that have been preliminarily probed fall into two broad categories: solar radiation management and carbon dioxide removal. Those in the first category are aiming to reduce the intensity of the sun’s rays hitting the Earth by making the atmosphere, clouds or Earth’s surface more reflective. But these approaches do nothing to treat the underlying cause of the problem – rising carbon dioxide levels. That means other major problems caused by anthropogenic carbon dioxide, such as ocean acidification would continue unabated. The technologies in the second category would reduce carbon dioxide levels in the atmosphere.

Cloud brightening is one solar radiation management approach being examined in labs and using computer models. No outdoor experiments have yet taken place. The idea is to spray sea salt particles into stratocumulus clouds above the ocean using remotely controlled ships with huge funnels. Water droplets naturally form around particles, so putting more sea salt in the clouds means more water droplets should form, and because these are reflective this should boost the clouds’ natural ability to reflect the sun’s rays.  

Forster has been leading an effort to model both the efficacy and potential side effects of cloud brightening as part of a UK-funded project called IAGP (integrated assessment of geoengineering proposals). ‘What we discovered was that this technology will be a lot more difficult than we thought at the beginning,’ he says. ‘The first problem we encountered with it is that only certain types of marine clouds are susceptible.’ The?models also suggest that getting the particles into the clouds will be more difficult than first?thought.  

Cloud brightening would probably also cause a general decrease in rainfall. ‘But a bigger problem is that you set up some quite peculiar geographical variations, for example you get a big decrease in rainfall for the [African] Sahel,’ says Forster. This is a big concern and more research is therefore needed to understand the viability of cloud brightening, he adds.

Mimicking volcanoes

Injecting reflective aerosol particles into the stratosphere is another technology currently being explored in the lab and using computer models. Again, no outdoor experiments have taken place. This approach mimics the natural cooling seen after large volcanic eruptions: volcanoes inject sulfur dioxide into the stratosphere, which converts into reflective sulfate aerosols. ‘After the Pinatubo eruption [in the Philippines] in 1991, we saw a fairly strong drop in global temperature associated with the increased scattering of sunlight,’ explains volcanologist Matthew Watson from the University of Bristol, UK. This cooling lasted for around two years. ‘That’s something we’re interested in potentially emulating.’

A number of groups around the world are exploring this possibility, and Watson is leading the UK-funded effort called Spice (Stratospheric Particle Injection for Climate Engineering). One aim of the Spice project is to identify a suitable aerosol particle for injection. ‘We’re interested in the question: can you do better than sulfate?’ says Watson. A suite of naturally occurring mineral aerosols, including silicon carbide, titanium dioxide and diamond, have been examined in the lab but so far the perfect particle remains elusive. Project members have also designed – but not built – a long pipe attached to a tethered balloon, filled with helium or hydrogen, through which aerosol particles could be pumped into the stratosphere. 

Using computer models, the Spice project is exploring the viability and potential side effects of these injections. Echoing Forster, Watson says that much more research is needed before any decisions on the suitability of sulfate aerosol injections can be made.  

Other solar radiation management techniques that have been considered are placing huge mirrors or billions of reflective balloons into the atmosphere, but neither of these are being widely investigated at present, owing to cost concerns. 

Symptomatic relief?

All of the solar radiation management approaches share a potentially disastrous concern, known as the termination effect. If humanity committed to using one of these technologies (without cutting emissions) and then suddenly stopped, global temperatures would – over a couple of years – return to where they would have been if the climate engineering had never happened. An extremely rapid rise in global temperature would therefore occur over a short period of time. ‘I think pretty much everyone agrees that would be horrific, absolutely catastrophic,’ says Watson, because there would be no time to adapt. 

This is one of the main reasons why Watson says he is agnostic about whether solar radiation management is a good idea or not. However, David Keith, a climate scientist at Harvard University, US, is a strong proponent of using sulfate aerosol injections alongside efforts to cut emissions. ‘What is clear is that if you want to manage the long term climate risk you must bring emissions to zero,’ says Keith. ‘But solar geoengineering allows you to reduce the risks in the short term, while we deal with emission cutting.’ 

His proposal is that the volume of sulfate aerosol injected is ramped up very gradually to stave off the worst of global warming, but limit the risk of unforeseen side effects of the technology. They could then be ramped back down again once emissions have been cut. ‘I think this approach will most likely provide benefits for most of the world and have risk at its most manageable and testable,’ he says.  

Keith believes the technology is now sufficiently mature to run small-scale outdoor experiments. ‘We are developing a stratospheric experiment that hasn’t run yet,’ he says. Small, in situ experiments under well regulated circumstances can begin to remove some of the uncertainties remaining from lab experiments and modelling, he adds. Keith plans to use a pre-loaded, propelled balloon that would stay in the stratosphere for a number of days distributing its load. There is no timeline for when these experiments may take place, however, owing to ongoing public and political concerns surrounding the whole field of climate engineering. ‘The idea of conducting experiments to alter atmospheric processes is justifiably controversial, and our experiment is just a proposal,’ he says. ‘It will continue to evolve until it is funded, and we will only move ahead if the funding is substantially public, with a formal approval process and independent risk assessment.’

Sucking up CO₂

Carbon dioxide removal technologies could potentially be used alongside emission cutting to limit global warming, with the added bonus of reducing carbon dioxide levels. Oceanic iron fertilisation is one such carbon dioxide-busting technology. Phytoplankton need iron to photosynthesise, and in around one third of the ocean, their growth and reproduction is limited by a lack of this micronutrient. Adding iron (probably in the form of iron sulfate) to these areas of the ocean, should boost photosynthetic activity, pulling extra carbon dioxide out of the Earth’s atmosphere. 

Modellers have taken a preliminary look at the viability of iron fertilisation and a few small-scale field experiments have also taken place. However, no field experiments have been undertaken since 2009, owing to governance concerns. Political and public apprehension has also squashed the availability of funding. ‘A lot of the funding organisations worldwide just feel this is too hot a potato,’ explains Richard Lampitt from the National Oceanography Centre in Southampton, UK. Lampitt coordinated the centre’s iron fertilisation research until funding ran out a couple of years ago. ‘That I think is very unfortunate. If we are going to make sensible decisions, they need to be evidence based,’ he says. 

‘Someone needs to do a fairly large experiment adding iron, or some materials that contain iron, to a fairly large area and looking at it for a prolonged period of time. Until that is done, with appropriate modelling to pull together the physics of oceans as well as the chemistry and biology, we’re not going to be in the position to really say whether this is likely to be a useful way forward.’

Other carbon dioxide removal technologies under consideration include afforestation – planting trees in areas where there were previously no forests – and converting biomass to biochar (charcoal) that can then be locked up in the soil. 

Whether climate engineering has a role to play in cutting global temperatures, or even just preventing them rising further, remains uncertain. But the clear message from the scientists working in this field is that with efforts to cut emissions still stalling worldwide, the need for research into the viability and risks of climate engineering, as a potential plan B, is necessary. ‘If we can’t do the right thing – conventional mitigation – correctly, then what chance do we have of doing the wrong thing – geoengineering – well without proper research?’ says Watson. 

Nina Notman is a science writer based in Salisbury, UK