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Solar radiation management is an extreme way to handle climate change and today nobody wants to do it; but if the world is forced to consider this geoengineering option seriously, how is it to be governed

Blocking sunlight is a controversial option to mitigate climate change. (Photo by Garry S.)

Blocking sunlight is a controversial option to mitigate climate change. (Photo by Garry S.)

The year is 2026. Country after country has failed to keep the promises made in the Paris Agreement, and climate change is gaining pace. Rising seas are eroding islands at a frightening rate. Some desperate governments get together and decide they must use geoengineering to block off at least a bit of the sunshine. They must use solar radiation management (SRM).

“Do not think of this as such a sci-fi scenario,” Arunabha Ghosh tells “Today almost the entire world is against geoengineering, especially large scale geoengineering such as SRM which will block off a part of the sunlight. But the way things are going, do not be surprised if, 10 years from now, this possibility is considered very seriously.”

Researchers are already considering it seriously. “I wouldn’t ever want human society to do this,” says Govindasamy Bala of the Indian Institute of Science, Bangalore. But he and his students are studying the prospects and the perils, just as volcanologists study volcanoes, though an eruption is the last thing they want. Internationally, there is even a Solar Radiation Management Governance Initiative (SRMGI).

SRM researchers from India and abroad came together recently in New Delhi at the call of the Council on Energy, Environment and Water (CEEW), the think tank headed by Ghosh. They discussed the science and governance of SRM.

Explaining why he took SRM seriously, Andy Parker, head of SRMGI, pointed out that since the start of the Industrial Age, humans had already put an extra 2.2 trillion tonnes of carbon dioxide in the atmosphere. Carbon dioxide is the main greenhouse gas whose excess in the atmosphere is causing climate change. At the current emission rate of around 40 gigatonnes of carbon dioxide per year, there are only 5.2 years left before the world crosses the aspirational ceiling of the Paris Agreement – to keep average global temperature rise within 1.5 degrees since the start of the Industrial Age.

Geoengineering options

So there is good reason to prepare for a pessimistic scenario. In theory, there are two types of geoengineering scientists can attempt.

They can inject sulphate aerosols in the stratosphere – the second highest part of the atmosphere – so that these aerosols reflect a portion of the sunlight back into space. That is SRM.

Or they can try to remove carbon dioxide from the atmosphere, store it underground by itself or after mixing with another chemical. This method is being tried, but so far it is prohibitively costly, to say nothing about the strong protests by climate activists against this or any other form of geoengineering.

Does SRM work?

The 1991 eruption of the Mount Pinatubo volcano in the Philippines has proved to scientists that SRM can bring down the temperature. The sulphate aerosols thrown into the stratosphere by that eruption brought global temperature down by half a degree Celsius the following year.

And artificial injection of sulphate aerosols into the upper atmosphere is not exactly rocket science. There are enough aerosols and to spare – largely those very small particles of the pollutant sulphur dioxide that is produced by incomplete burning, whether in cook-stoves, cars or thermal power stations. There are planes with nozzles to spread the aerosols, and pilots experienced in cloud seeding, which spreads another chemical the same way.


Does SRM really work?

So SRM can bring down the temperature and arrest that effect of climate change to a certain extent. But what about the other big effect, on rainfall and snowfall, what scientists lump together as precipitation?

SRM will be of little help there, Saroj Kanta Mishra of Indian Institute of Technology Delhi said at the meeting. Bala went further and said his modelling-based studies showed SRM would “weaken the global water cycle”.

The Intergovernmental Panel on Climate Change (IPCC) has said earlier that climate change has already affected the water cycle. Now there are fewer rainy days, but more intense rainfall on those days.

Acidic oceans

Bala pointed out that SRM would have zero effect on another consequence of climate change – ocean acidification. As carbon dioxide concentration rises in the atmosphere, more of it reacts chemically with seawater to form a weak acid. The build-up of this acid in seawater is killing corals, the home of much marine life and the nursery of most.

And in a hypothetical SRM-controlled atmosphere, what if the world decided to stop injecting sulphate aerosols into the stratosphere? The effect would be far worse than stopping a diet. Bala said his models forecast the warming rate would go up 20 times.

There are other risks too. As Parker pointed out, starting SRM may make some governments feel they did not bother to cut greenhouse gas emissions any more. This would be all the more tempting because SRM is a cheap technology, relatively speaking. The cost would be in tens of billions of dollars per year, but not in trillions.


Even after knowing all this, what if one or more countries felt compelled to try SRM? Where would they do it? There are three choices – uniformly all over the world, over the tropics, or over the poles, arctic, Antarctic or both.

Some scientists have said the poles would be better because the cold weather would keep the aerosols from dispersing as widely as they would otherwise. But Bala warned – and his student Aditya Nalam showed with lots of models – that injecting aerosols only over the arctic would push away the entire tropical rainfall belt, which would be disastrous for South Asia. “If it must be done, it is better to do it uniformly,” Nalam said.

The threat of SRM has already drawn a strong response. The UN Convention on Biological Diversity has placed a moratorium on all outdoor climate engineering research. When the IPCC recently selected what it would study for its next special report on what the world needs to do keep average global temperature rise within 1.5 degrees Celsius, it decided to ignore all forms of geoengineering, including SRM.

Governing SRM

But somebody needs to discuss how to govern SRM if it becomes reality, said Chen Ying of the Chinese Academy of Social Sciences. She thought that the UN Framework Convention on Climate Change provided the best forum for such a discussion.

Shinichiro Asayama of the National Institute for Environmental Studies, Japan, said that geoengineering and migration of affected people were the two extreme forms of adaptation to climate change. Since people were already discussing migration, he saw no reason why they shouldn’t discuss geoengineering. He had run a survey among college students in various Asian countries and had found his respondents were ready to discuss it.

Explaining why he thought the world may be compelled to discuss geoengineering, including SRM, Ghosh pointed out that in the last few years, India had been spending around USD 90 billion a year to adapt to climate change and to deal with its impacts such as drought, flood, storm, heat wave and sea level rise. So, in his opinion, all methods to deal with climate change may have to be discussed, including current taboos among climate activists, such as large dams and nuclear power, or even SRM.

“We need public participation in deciding whether to go ahead with geoengineering,” Ghosh said. If something as big as intentional tampering with the atmosphere to screen sunlight becomes inevitable, it is better that it be done with full public participation and transparent international governance rather than in secrecy.


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