How clouds could be engineered to cool the Earth

Scientists are actively exploring – on a theoretical basis – what it might take to cool the Earth if governments, businesses and individual actions collectively fail to do so in the next 15+ years. But, in nearly every case, the potential downside of such scientific actions aren't yet known, and there is no regulatory mechanism yet in place to govern or monitor the efforts, several leading scientists argue in Science this week.

Two approaches:

1. The leading geoengineering theory, according to scientists, is essentially a large science experiment on a global scale that mirrors what clouds do naturally. It would diminish the sun's warming effects by continuously injecting sulfur particles into the stratosphere, thus filtering out some of the radiation entering our atmosphere.

• Pros: Most scientists agree it would change the temperature on Earth.
• Cons: It could have a dramatic (and unintended) effect on the Earth's major water cycles, like the monsoon, that provide fresh water necessary for billions of people to live.
• Other unknowns: how effective it might be, or how much it might cost. (Initial estimate are on the order of $20 billion a year for a century or more, they wrote.)

2. A second approach is to artificially create thin cirrus clouds at low-altitude that trap less heat and would cool the Earth.

• Risks: These artificial clouds would attract moisture, and could upset the Earth's water cycles as well. And if this grand science experiment was done poorly, it could actually heat the planet instead of cool it.

What's needed: Janos Pasztor, the former climate policy lead at the United Nations (who now leads a geoengineering institute affiliated with Carnegie) argues that all of this means government leaders need to move quickly to understand the profound implications of both the research and its potential impacts. There is also an immediate risk that just one country, a small group of countries or even a very wealthy individual could unilaterally deploy a planet-wide solar radiation management scheme before anyone truly understands the potential risks.

Go deeper: Read our Expert Voices conversation on the topic.