Cooling the earth down

“Stratospheric aerosol injection, the boldest and also the most risky of climate engineering interventions, involves spraying into the stratosphere fine, light-coloured particles designed to reflect back part of the solar radiation before it reaches and warms the earth." Image shows the tethered balloon method to inject sulfate aerosols into the stratosphere. Photo: Wikimedia Commons, Source: CC BY-SA 3.0  

The >Paris Conference last year primarily discussed plans to >reduce carbon emissions, which is understandable as this is the most immediate item for action. But other measures for dealing with global warming, in particular climate engineering, may soon acquire more importance.

Today, climate engineering efforts are viewed either as secondary measures to be undertaken alongside reducing emissions or as technologies which have not matured enough to warrant discussion by world leaders. But the situation can change dramatically in the future. Even if all the national commitments made in Paris are fulfilled, the effects of >global warming will inevitably worsen in the near term. As nations struggle to reduce emissions even further, alternative solutions using engineering innovations will increasingly gain currency.

R. Rajaraman

A variety of such proposals for battling global warming are already on the table — a few are being tried out and others are being seriously researched. Unfortunately, some of them also carry the risk, if things go wrong, of causing unintended environmental disasters. Climate engineering experts have been addressing these problems for years but such awareness has not trickled down to the larger intelligentsia to form a body of educated opinion that can help governments decide on which techniques to adopt and how best to govern and regulate them.

Control carbon or sunlight or both?

Most climate engineering efforts can be divided into two categories which address, respectively, the management of carbon and the management of sunlight. The first category is directed towards removing greenhouse gases from the atmosphere. A prominent example is carbon capture and storage (CCS), where some of the carbon dioxide (CO 2) being emitted by coal-fired power stations is recaptured by physically sucking it in and transporting it elsewhere to be sequestered underground. The first 115 MW CCS retrofitted coal power plant commenced operation at Boundary Dam in Canada in 2014. The CO 2 captured there is transported and pumped into nearby oilfields for enhanced oil recovery. This has reduced its CO 2 emission by one million tonne each year. Studies are on in the U.K. and other nations on the feasibility of similar installations there.

Another method for removing CO 2 from the atmosphere is to increase forest cover as plants will absorb some of the unwanted CO 2. Increased forestation is part of India’s strategy for reducing CO 2.

It is not clear whether CCS, reforestation and other carbon removal methods can make sufficient impact at the global level to significantly slow down global warming. But they seem relatively benign at the scale at which they are being considered now and will at least lower CO 2 pollution locally.

More ambitious, but also more worrisome, is the second category of climate engineering: solar radiation management (SRM). Here the plan is to reduce global warming by cutting down the heat absorbed by our planet from the sun. Among the techniques being considered are marine cloud brightening, cirrus cloud manipulation and stratospheric aerosol injection (SAI). SAI, the boldest and also the most risky of climate engineering interventions, involves spraying into the stratosphere fine, light-coloured particles designed to reflect back part of the solar radiation before it reaches and warms the earth. SAI proponents claim that this could bring down the global temperature by as much as 1°C — a substantial amount in the climate change context.

This is neither science fiction nor fantasy. Much preliminary research has already been done on this technique and reviewed in major journals. The optimal gases for injection, such as sulphur dioxide (SO 2), can be produced in abundance. Furthermore, just a few airplanes specially redesigned for the purpose may suffice for injecting the required aerosol into the stratosphere. There are also precedents from nature. The 1991 volcanic eruption of Mount Pinatubo in the Philippines injected 20 megatonnes of SO 2 into the stratosphere, cooling the globe significantly for a couple of years.

But SAI also has the potential for disastrous side effects, crossing national boundaries. The Pinatubo volcanic eruption is also said to have reduced precipitation, soil moisture, and river flow in many regions. Injection of sulphur compounds into the stratosphere is likely to increase acid deposition on the ground and also contribute to ozone layer depletion. Apart from such “known unknowns”, there could also be, to use the catchphrase, the “unknown unknowns”.

The global climate system is too complex for current computational techniques to predict all possible consequences of tampering with it. Once the aerosol has been injected into the atmosphere, it cannot be removed. Yet, if for any reason the injection, once begun, is discontinued prematurely, there can be rapid re-warming. That, ironically, could do more damage than the gradual global warming that we are seeking to combat.

SAI research is still at a theoretical and laboratory level. Development of these techniques to large-scale deployment is years away. In that case, why should the larger community worry about it now? The reason is SRM interventions could happen sooner than one thinks. The technology does not seem to be astronomically expensive by standards of national budgets. Using a few airplanes to inject the necessary amount of aerosol to bring the temperature down by one degree could cost only a few billion dollars — well within the reach of even developing countries.

Flashpoints of the future

As climate change worsens, some coastlands could go underwater and other regions could suffer extreme heat and severe droughts causing massive human suffering. Under such pressure, and in the absence of international regulatory regimes, the affected nation, even a small developing one, may well resort to using whatever SAI technology is available by then in the international market. In their desperation, possible harmful effects on other countries may not weigh heavily on their decision-making. Meanwhile, just the fear of possible adverse side effects could lead other nations to take preventive action against the “perpetrator”. Nations have gone to war for less.

One simple way to deal with this problem is to just ban further research in these fields. In fact, some climate scientists have already suggested this. They also fear that even the possibility of SRM interventions may undermine efforts to reduce carbon emissions. But a blanket ban on SRM would be unwise and difficult to implement. Technology, benign or malevolent, has a way of continuing to advance. Besides, banning all SRM research will amount to throwing the baby out with the bathwater. The goal of SRM is to mitigate damage done by carbon emissions. If there is some chance of it succeeding safely, it would be unwise to abandon it at this stage. Abandonment would also leave SRM technologies dangling midway, insufficiently tested or refined. That may nevertheless not deter some desperate >climate change-afflicted nation from deploying it, leading to disaster.

It is only through continuation of responsible research in climate engineering, done under proper regulatory oversight, that the limitations and risks of such interventions can be fully understood and provide the basis for informed decision-making. That will call for international governance mechanisms for overseeing the research and development and possible deployment of climate engineering techniques. This will take years to negotiate and set up. Criteria for permissible work will have to be developed, along with expertise for verification of compliance.

While active climate engineering researchers have already been conscientiously worrying about these issues, it is not too early for the rest of us to start thinking about it.

(R. Rajaraman is Emeritus Professor of Physics at JNU.)

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Printable version | Jan 25, 2022 8:08:48 AM |

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