NEW YORK: As the world struggles to cut back on greenhouse gas emissions, concerns remain over a controversial climate solution that involves redirecting sunlight into space to cool the earth.

Scientists who have studied the field for decades say this approach, known as solar geoengineering, is not fully understood and does not address the root cause of climate change.

“If you’re very sick, and you have no other alternative, you can try chemotherapy. It might make you very sick, it might kill you, but if it’s the last option you have, you might try it,” environmental legal scholar Michael Gerrard told CNA.

“With solar geo-engineering, it is the very last resort,” added the Andrew Sabin Professor of Professional Practice at Columbia Law School.

WHAT IS SOLAR GEOENGINEERING?

Solar geoengineering, also known as solar radiation modification or solar radiation management, aims to reduce the amount of solar radiation hitting the earth’s surface in order to cool it.

One proposed method, called stratospheric aerosol injection, remains mired in controversy and debate despite increasing investment interest.

The goal is to create conditions in the sky that naturally occur when volcanoes erupt and spew particulates into the air that can cool the planet.

Delivery systems - such as customised aeroplanes, high-altitude balloons or blimps, or even artillery - are deployed to spray reflective sulphate aerosol particles into the stratosphere, like those from a volcanic eruption.

These tiny reflective particles then redirect sunlight away from earth and into space.

Another approach to solar geoengineering is marine cloud brightening, which seeks to make low-lying clouds more reflective by spraying microscopic seawater droplets into the air.

Trials have been underway at the Great Barrier Reef since 2017.

CONCERNS OVER ETHICS

However, ethical concerns have emerged over such solar geoengineering concepts.

Gerrard noted that the practice can have “massive side effects that we (can’t) even begin to understand”.

“All of life on the planet has evolved over aeons based on the amount of sunlight hitting the earth. Our vegetation, the oceans, have evolved to reflect the amount of sunlight,” he said.

“If we alter that, we have very little idea what it’ll do. The second, third, fourth effects are completely unknown, and so it is scary - it is even (more) terrifying to do this on a large scale.”

Researchers have also said solar geoengineering carries the risk of taking attention away from real action to fight climate change.

While it could be part of the solution to slow down global warming, they said it cannot replace the phasing out of fossil fuels and moving towards net-zero emissions as soon as possible.

NO OVERSIGHT

Gerrard also pointed out the lack of governance on solar geoengineering.

“It could be done unilaterally by a country, or even a very rich individual, without requiring any kind of special permits … there is no international agreement, and almost no national or subnational governance of solar geoengineering,” he added.

He said this could lead to international tensions if agreements are not adopted.

Earlier this year, governments at the United Nations Environment Assembly held in Kenya’s capital Nairobi were unable to reach a consensus on how the UN should regulate solar geoengineering techniques.

Switzerland had submitted a proposal for the world body to study the risks and opportunities, but it withdrew its draft resolution after strong opposition from other nations.

While several private companies in the United States said they are already using the technology, experts rebuked the claims could be full of hot air.

“This is an effort by a couple of non-scientists to engage in experiments that have not undergone peer review or any other scientific review. There are major questions about whether they would have any beneficial effect,” Gerrard said.

'The very last resort': Why solar geoengineering remains a controversial climate solution