Why top scientists oppose the idea backed by Bill Gates to curb global warming

In the not-too-distant future, Earth faces the tragic consequences of an experiment designed to stop climate change: dumping chemicals into the sky to form a barrier against the sun’s planet-warming rays.

The attempt fails and the world enters a post-apocalyptic reality.

That is the plot of “Fear Express”, a 2013 film directed by South Korean Bong Joon-Ho, the renowned filmmaker of “Parasite”.

But not everything the film raises is science fiction. That possible strategy against global warming that the film talks about exists in reality: it is the principle of solar geoengineering.

There is a research center at the prestigious Harvard University in the United States dedicated to studying this concept.

the billionaire Bill Gates is one of its great enthusiastsand has donated millions to his research.

Also real is the monumental task we have to limit the global temperature increase to 1.5°C and that climate catastrophes will be a routine thing in the world in the near future.

Last Monday, April 4, the arm of the United Nations Organization (UN) dedicated to climate change published a new report, which brings an ultimatum: it is now or never if we want to avoid severe droughts, extreme heat, devastating floods and mass extinction of species.

If the established goals are not achieved and the changes have modest results, the average temperature in the world will increase in a range between 2.1°C and 3.5°C.

Getty Images
The founder of Microsoft is funding solar geoengineering research.

Some experts fear that solar geoengineering will gain traction as a solution in this time of desperation, even though there is a possibility that cause irreversible side effects environmentally and politically dangerous: the technique could be used as an unpredictable weapon of war, they warn.

But others affirm that one cannot give up looking for solutions in the face of the urgency of climate change, a line of reasoning adopted by Bill Gates.

In January of this year, more than 60 scientists from several countries launched an initiative to directly prohibit the development of the techniquewhich has only been studied in computer simulations and requires field testing.

That proposal warns that, in addition to potentially disastrous results, solar geoengineering would not fully resolve the problem of global warming, a point admitted by supporters of the concept.

Y could divert attention of the most important obligation that has been ignored: that of significantly reducing emissions of carbon dioxide (CO2), which traps heat in the atmosphere.

BBC News Brazil spoke to five scientists from Brazil and the US, some critics and some supporters, to explain the implications of solar geoengineering.

How does it work?

The eruption of the Pinatubo volcano in the Philippines in 1991

ARLAN NAEG/Getty Images
The eruption of the Pinatubo volcano in the Philippines in 1991 lowered the temperature of the planet in the following years.

There are different techniques that are classified as solar geoengineering, including some that work on ocean waters rather than the atmosphere.

However, the principle of the most debated technique today is inspired by the great volcanic eruptions and is called aerosol injection into the stratosphere.

In 1991, Mount Pinatubo in the Philippines caused the second largest volcano eruption in the 20th century, leaving more than 800 dead and 10,000 homeless, in addition to a trail of destruction.

A natural phenomenon was also observed: the lava and ashes expelled by Pinatubo caused tons of sulfur dioxide in the stratosphere to act as a kind of mirror for the sun’s rays.

“When there is a lot of soot and solid particles in the upper atmosphere, solar radiation meets these aerosols when it enters the atmosphere and is reflected back into space,” explains Tércio Ambrizzi, professor at the Institute of Astronomy, Geophysics and Atmospheric Sciences of the University of São Paulo (USP).

“Solar radiation cannot pass and reach the Earth’s surface, preventing it from generating a high temperature,” he adds.

The scientists noted that the effects of the Pinatubo volcanic activity in 1991 led to a 0.5°C drop in global temperature in subsequent years, a rate considered significant.

“The idea of ​​solar geoengineering is to inject aerosols into the stratosphere to inhibit that influx of solar energy. And with that you would be inducing a chillsays Ambrizzi.

Graphic showing how solar geoengineering works


“We know that the reason for the disappearance of the dinosaurs was the fall of a meteorite. There is a theory that the impact caused a series of volcanic explosions around the planet, generating an aerosol layer that prevented the entry of solar energy and global temperature dropped“.

To try to reproduce the phenomenon, the idea is to build special planes to reach the stratosphere (in a range of about 20-30 km altitude) and drop chemical compounds, such as sulfates and their variations.

This goal is considered quite doable from a technological point of view.

Another factor in favor of solar geoengineering is its cost: $10 billion a year is the highest estimate, low compared to future losses from global warming, already estimated in the trillions.

But Stephen M. Gardiner of Washington State University, who studies ethical issues in environmental problems and their impact on future generations, says there is consensus “among responsible scientists” that the concept remains highly speculative.

“Even if we decided to push research hard in this field, it would be a race against time to develop something that would only be put into practice decades from now and would inevitably involve a big risk“.

Thermometer in the city of Toulouse during a heat wave in France.

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Thermometer in the city of Toulouse during a heat wave in France.

For Gardiner, the growing attention to solar geoengineering is a product of the desperation that grips those who are aware of the climate catastrophe on the horizon.

“It’s getting out of control. It is difficult to deal with the persistent failures of conventional approaches, such as the Kyoto and Paris (climate) agreements.”

“So people are starting to latch on to anything. even to events highly speculative, inherently risky and potentially geopolitically destabilizing like this”.

The University of Washington professor says solar geoengineering would involve a deep concentration of political power and would require new global institutions more powerful and more ethical than the ones we have today.

“Without that, who would wield the power of geoengineering? It seems inevitable that in this way it would be a superpower, which would create conflicts with other great powers,” says Gardiner.

Ambrizzi, from USP, says that “there is no control over where the aerosols injected into the atmosphere go. Because in the upper atmosphere there are wind flows, there is an intense circulation in the stratosphere”.

“Without that check, regions that are balanced can be destabilizedas“.

“Let’s suppose that Brazil decides to do this experiment, but Argentina does not. The average temperatures begin to drop here, but they increase in Argentine territory or decrease much more than the current ones”.

“The Argentine government has not given its consent for that. Imagine, for example, that the country loses all its wine production and decides to sue Brazil”.

It also points out the high degree of uncertainty existing in current weather and climate forecast models, reinforcing the unpredictability of solar geoengineering at its current stage.

In defence

David Keith, a professor of applied physics and public policy at the Harvard Kennedy School, is one of the main names cited when discussing the subject.

“My reading is that there is strong evidence that solar geoengineering could significantly reduce some climate risks in the second half of this century,” says Keith.

“Climate models consistently show that a combination of uniform and consistent solar geoengineering and emission reductions would reduce mean and maximum temperatures more than emission reductions alone.”

Traffic in Sao Paulo

AFP via Getty Images
Critics say solar geoengineering could distract from the main goal: reducing carbon emissions in the atmosphere.

“Given the evidence that an additional 1°C rise would hurt the planet’s warmest regions the most, and given that the poorest and most vulnerable are concentrated in these hot regions, it seems likely that solar geoengineering would be particularly effective in reducing risks in these places“, Add.

Holly Jean Buck – author of “After Geoengineering: Climate Tragedy, Repair and Restoration” – defends this technique due to the risks posed by climate change.

He agrees that it is necessary to understand what the impacts of solar geoengineering would be on the planet and that many studies are needed before putting it into practice.

“However, the request [contra el desarrollo de la técnica] requires measures that would affect the ability to fund, conduct and evaluate research transparently”.

Both acknowledge that there is a risk that solar geoengineering distracts from the main focus, reducing carbon emissions, and that the technique only works as an adjunct to that goal.


Emilia Wanda Rutkowski – professor at the Faculty of Civil Engineering, Architecture and Urbanism of the State University of Campinas (Unicamp) – was one of the signatories of the document that calls for a moratorium on the development of solar geoengineering.

Trying to find a solution without changing the essence of the problem [del calentamiento global] it’s not a real solution,” says Rutkowski.

She affirms that the problem is “dilating”.

“Why don’t you start with what you know is the principal cause?” he wonders.

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