Solar geoengineering — a series of steps designed to reduce the amount of solar energy that reaches the surface of the Earth — is starting to be talked about at the highest levels of climate science, Almost everyone agrees it is a lousy idea, one that is fraught with incalculable danger. Yet human greed, ignorance, and stupidity make it unlikely people will choose the best course, which is to drastically reduce our reliance on oil, coal, and methane to create heat or generate electricity.That leaves solar geoengineering as the least worst alternative among a series of bad choices.

Jim Hurrell is a one of the world’s leading climate scientists. He is a professor of Environmental Science and Engineering at Colorado State University. He is also a member of the World Climate Research Program, an organization that coordinates climate research initiatives at an international level. The science activities it supports address cutting edge topics which cannot be tackled by a single nation, agency or discipline alone.

WCRP meets globally in the Open Science Conference about every ten years. At the last conference in 2011, hardly anyone was talking about geoengineering. But this year, things were different,  Hurrell tells The Economist (Paywall. The source article has been republished by Yahoo! Finance.)

Solar Geoengineering Gains Traction

At this year’s Open Science Conference in Rwanda, Hurrell gave a keynote address on the subject of solar geoengineering. There were “hundreds of papers and talks and posters” on the topic he says, which is indicative of a broader shift in thinking. Although solar geoengineering has been the subject of serious scientific interest for years, it has been largely shunned by environmental NGOs and politicians. That is starting to change, Hurrell says.

Since the start of this year, solar geoengineering, sometimes known as solar radiation modification (SRM), has been the whole or partial focus of reports published by the European Commission and Parliament, the American government, the Climate Overshoot Commission, and four separate  parts of the UN. A common thread in all of them was that, given the world’s failure to cut greenhouse gas emissions fast enough, the pros and cons of SRM should be properly examined.

The Climate Emergency Explained

When light from the sun reaches Earth, about 70% of it is absorbed. The rest is reflected back into space by clouds, ice and the like. That absorbed energy is eventually re-emitted as infrared radiation. But not all of it makes it back into space. Greenhouse gases such as carbon dioxide absorb infrared radiation, trapping some of the re-radiated heat.

At first unwittingly, then knowingly, humans have been thickening that atmospheric blanket. The amount of carbon dioxide in the atmosphere has risen from around 280 parts per million before the Industrial Revolution to 417 parts per million last year. That has trapped more heat, raising average temperatures by around 1.2°C over the same period.

Most plans to tackle climate change aim to fix the problem by replacing fossil fuels with wind, solar, and nuclear power — sources that do not produce greenhouse gases. Solar geoengineering addresses the other side of the equation. Rather than allowing more energy to escape from the Earth’s surface, it aims to stop some of it from arriving in the first place by increasing the Earth’s tendency to reflect sunlight — known to scientists as albedo.

Nature has already done the proof of concept work, the Economist says.  The Earth’s albedo can be temporarily altered by volcanic eruptions, which spew particles and gases into the air. Sulfur dioxide is particularly influential because of how it combines with water to form sulfuric aerosols which make a light-scattering haze in the sky. In 1991 Mount
Pinatubo, a volcano in the Philippines, sent 15 million tons of it into the atmosphere — enough to cool the planet by about 0.5°C for well over a year.

The best researched version of solar geoengineering relies on the same mechanism. The idea is to inject sulfur dioxide or other chemicals such as calcium carbonate or powders made of aluminium or diamonds not into the troposphere but into the stratosphere, which begins about 20 km above the surface of the Earth.

Those particles would be distributed more widely than those from volcanoes and would remain in the atmosphere longer, which means fewer of them would be required for a given level of planetary cooling. By some estimates, reflecting enough extra sunlight to suppress average temperatures by 1°C would require the injection of roughly 2 million tons of sulfur into the stratosphere annually.

That is far less than is produced by volcanic eruptions and the burning of fossil fuels and might cost a few tens of billions of dollars annually. By contrast, the cost of decarbonzing the world economy runs into the trillions of dollars each year. While that makes solar geoengineering sound like a bargain, worries abound.

Is Solar Geoengineering An Unacceptable Risk?

The European Commission said earlier this year that, given the current state of development, solar geoengineering “represents an unacceptable level of risk for humans and the environment.” The Climate Overshoot Commission recommended that countries should put a moratorium on the deployment of geoengineering, including any large scale outdoor experiments or any activity with a “risk of significant trans-boundary harm that could do damage across national borders.

Three years ago, Sweden banned a proposed experiment in the Arctic designed to study how sulfur dioxide injection into the upper atmosphere might work. Mexico has banned such experiments.

Less Expensive Options

Some worry that solar geoengineering might affect world weather patterns, Early attempts to study the  issue assumed enormous levels of sulfur injection. But the modelling suggested such drastic changes in the energy balance in the upper atmosphere could play havoc with tropical monsoons — the seasonal rains which the agriculture and economy of many countries depend upon.

Later research, using more realistic numbers, was more reassuring. In 2020, academics at Harvard University concluded that dimming the sun by less than necessary to completely offset the existing level of warming would not significantly alter rainfall in most places in the world. In the areas where it did, it seemed to result in more water rather than less.

The effect that spraying aerosols might have on stratospheric chemistry is also unclear. It could, for instance, amplify chemical reactions that break down ozone molecules, slowing the recovery of the ozone layer and allowing more cancer causing ultraviolet radiation to reach the ground.

Rising carbon dioxide levels do more than just heat the planet. A good deal of the gas is absorbed by the oceans, where it forms carbonic acid. As a result, the Earth’s oceans are more acidic than they have been for at least 2 million years. Since solar geoengineering does not reduce carbon dioxide emissions, it would do nothing to solve that problem.

The fact that some level of solar geoengineering could be relatively inexpensive also raises concerns. An analysis by Wake Smith, a geoengineering researcher at Yale University, tried to model the cost of solar geoengineering in 2100 and concluded it might cost around $30 billion a year in 2020 dollars to hold temperatures at the levels they would have reached in 2035.

As Smith points out, that is roughly what Americans spend on pet food each year. Such a sum is easily within reach of a single big economy or a coalition of smaller ones. That raises the specter of a country that wants the cooling consequences of solar geoengineering  deciding to deploy the technology against the wishes of other nations. If anything can be weaponized, humans will figure out how to do so.

Solar Geoengineering And Moral Hazard

Perhaps the most pervasive fear around solar geoengineering is its moral hazard. By offering a cheaper alternative, it could undermine attempts to fix climate change by doing the hard work of cutting greenhouse gas emissions. Nations are rushing to embrace carbon capture — a technology which does not yet exist at any useful scale but which underpins almost all long term emission reduction plans.

The Economist suggests that countries will seize on anything that allows them to avoid painful emissions cuts. People more open to the idea retort that geoengineering could be used to buy more time for those emissions reductions to happen, and keep temperatures lower in the meantime, an idea they refer to as “peak shaving”.

2023 will almost certainly be the hottest year on record. Berkeley Earth sees a more than 90% chance of 2023’s average temperature exceeding 1.5°C above pre-industrial levels — making it the first year hotter than the lower of the two Paris Agreement temperature targets. Jim Hurrell says that what is needed is a serious research program into the feasibility of solar geoengineering run by an institution like the IPCC or the World Meteorological Organisation. He thinks such an endeavor would probably form the basis of a strong argument against SRM, rather than support for deploying it.

Policymakers, too, seem increasingly interested in exploring the pros and cons of solar geoengineering. Janos Pasztor runs the Carnegie Climate Governance Initiative, which encourages discussions about various climate technologies including SRM. Initially, he says, solar geoengineering was seen as unpalatable. Now, politicians and officials discuss whether it might have a role in climate policy after all. None of those his organization has spoken with are opposed to further research into the idea.

Perhaps the biggest shift has come in poor countries, which have the most to lose from both rising temperatures and any unintended consequences of solar geoengineering. Anote Tong is a former president of Kiribati, a low-lying Pacific island state menaced by rising sea levels. Last year he told The New Yorker that, should the world continue on its current path, it would soon reach the point where “it has to be either geoengineering or total destruction.” Those are not the words of a man who believes that countries like his have many other options, the Economist points out.

A Disagreement Between Science Leaders

Recently, James Hansen and Michael Mann have expressed differing views on how quickly the Earth is warming. Hansen, who first testified to Congress about carbon dioxide in 1988, thinks the rate of change is increasing. Mann, a co-author of the “hockey stick” graph, disagrees.

Such disputes give aid and comfort to those who would destroy the Earth for profit, which is the greatest moral hazard of all. We may in fact “science our way” out of the global heating crisis, but doing so will only demonstrate beyond a reasonable doubt that humans are incapable of preserving their home planet if left to their own devices.

We are like a virus that consumes every available resource even if it means destroying its host. We may yet figure out how to keep the Earth habitable for humanity but if we do, it will stand as an indictment of our species rather than a triumphant moment in human history.

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• Source: https://cleantechnica.com/2023/11/24/geoengineering-least-worst-climate-solution/