Dozens of scientists jointly opposed the use of "artificial volcanic ash" to block out the sun to cool the earth.

On January 17, more than 60 international policy experts and scientists collectively spoke out about the potential dangers of geoengineering projects to lower the earth's surface temperature to slow global warming, and called on the government to stop such projects.

These include the solar radiation intervention (solar radiation modification,SRM) project, which has been hotly discussed in recent years. The project plans to inject billions of sulfate particles into the middle atmosphere to reflect sunlight, but experts argue in an open letter that the result could do more harm than good.

"Solar geoengineering cannot be regulated fairly, widely and effectively on a global scale." A review in the journal WIREs Climate change (WIREs Climate Change) also supports this view, the letter said.

"therefore, we call on governments, the United Nations and others to take immediate policy action to prevent the formal establishment of solar geoengineering, which is one of the climate policies."

Compared with the mid-19th century, the earth's temperature is now 1.1 degrees Celsius higher, which has increased the intensity, frequency and duration of deadly heat waves, droughts and severe storms. Countries around the world have pledged to limit the warming of the earth's surface to 1.5 degrees Celsius higher than in the mid-19th century, but UN-backed scientists say that threshold could be broken within a decade.

Unable to reduce greenhouse gas emissions that drive global warming, some policy makers have decided to embrace solar geoengineering to buy time for more sustainable solutions. Not long ago, the project was widely seen as a science fiction rather than a science project.

It has long been known that injecting large amounts of reflective particles into the upper atmosphere can cool the earth. Nature sometimes does the same: in 1991, ash from the eruption of the Mount Pinatubo volcano in the Philippines cooled the average temperature of the earth's surface for a year.

But the open letter offers several reasons for rejecting the project. Several studies have shown that artificial weakening of solar radiation is likely to disrupt monsoon rains in South and West Africa, thereby destroying Rain Water's irrigated crops, on which hundreds of millions of people depend.

An accident.

"the injection of sulfate particles into the stratosphere weakens the summer monsoon in Africa and Asia, leading to drought in the Amazon." The Intergovernmental Panel on Climate change (Intergovernmental Panel on Climate Change,IPCC) mentioned it in a recent scientific assessment.

However, other regions may benefit: a study last year concluded that SRM could significantly reduce the risk of drought in South Africa.

Scientists are also concerned that if the injection of solar radiation blocking particles is suddenly stopped, the so-called "termination shock" phenomenon may occur. "if SRM is terminated for any reason, the temperature on the earth's surface will rise rapidly, which is very likely to happen." IPCC commented.

In addition, the technology does not help to end the continuous accumulation of carbon dioxide in the atmosphere, which is the culprit that really changes the chemical composition of the ocean.

The letter also warns that the more you want to solve the climate problem quickly, "the less governments, businesses and society will do their best to achieve decarbonization or carbon neutralization as soon as possible."

Finally, there is no global management system to regulate or implement solar geoengineering. If a country, or even a billionaire with rockets, has already taken action, they will not face any regulation.

Therefore, the open letter calls for an "international non-use agreement", banning national investment and bad outdoor experiments, and refusing to grant patents to SRM technology.

The open letter also mentioned that such an agreement "will not prohibit similar atmospheric or climate research". Other forms of solar radiation intervention include spreading salt particles from the ocean over the ocean to brighten sea cumulus clouds, or setting up giant mirrors in space to reflect sunlight from Earth. Less controversial technologies include whitening roofs and road surfaces, or diluting the color of crop leaves through transgenic technology.