We Can Manipulate the Atmosphere Like Never Before

After a deluge of record-breaking rainfall this week, citizens of the United Arab Emirates and Oman are still trying to return to regular life. The storms forced schools, offices, and businesses to close, transformed the tarmac of Dubai’s international airport into a rippling sea, and killed more than 20 people across both nations. The downpour seemed almost apocalyptic: On Tuesday, the UAE received the amount of rain that usually falls in an entire year.

Early reports of the weather event prompted some speculation that it was worsened by a controversial weather-modification technology. The practice, known as cloud seeding, involves spraying chemical compounds into the air in an effort to wring more rain out of the sky. The United Arab Emirates carries out hundreds of these operations every year in an effort to supplement its water resources in the arid landscape. Exactly how well cloud seeding actually works is an active debate among scientists, but the technique can’t produce rain clouds out of thin air—it can only enhance what’s already there.  

The consensus, for now, seems to be that cloud seeding is unlikely to have contributed significantly to this week’s historic inundation. (The UAE’s meteorology agency said no seeding missions were conducted before the storm.) But the event raises anew some fundamental questions about interfering with nature. Cloud seeding is a type of geoengineering, a set of technologies aimed deliberately at influencing or altering Earth’s climate systems. The warmer our planet becomes, the more attractive geoengineering seems as a way to slow or endure the effects of climate change—and the less accurately we can predict its effects. Scientists can’t be sure that playing God with the atmosphere won’t cause human suffering, even if it is intended to alleviate it.

In the case of cloud seeding, humans have been playing God for decades. The technique dates back to the 1940s and has been deployed regularly around the world since to provide relief to regions parched by drought, clear skies ahead of Olympic Games, and give ski resorts an extra inch of snow. Scientists have been studying cloud seeding all along, but they’ve only recently managed to document how the technique might actually work, distinguishing between natural precipitation and precipitation that resulted from human intervention. Experts believe that seeding can squeeze out a small amount of additional precipitation, but it is “notoriously difficult” to determine how well it worked in any particular instance, Janette Lindesay, a climate scientist at Australian National University, told me.

[Read: The chemist who thought he could harness hurricanes]

The basics of cloud seeding are straightforward, Lindesay said: If you want rain, you release chemicals that encourage clouds to produce larger water droplets, which are more likely to reach the ground. If you want to suppress rain, you use chemicals that foster the creation of smaller droplets. But the simplicity belies the complicated science and high stakes of manipulating the atmosphere in the 21st century. The 2020s are becoming defined by a warmer atmosphere capable of holding more moisture, conditions that can lead to more extreme and unprecedented weather events, including intense rainfall. Add in geoengineering, and things can get risky. “We are in territory now where we can’t necessarily rely on past experience and past outcomes to inform us,” Lindesay said, of “what is likely to happen when we intervene.”

As geoengineering goes, cloud seeding is a rather limited technique, with small effects confined to small geographical areas. (That’s part of the case against seeding as a significant contributing factor to this week’s flooding in the Middle East; as Amit Katwala pointed out in Wired this week, parts of the UAE where seeding typically does not occur experienced torrential rain too.) But it can still be fraught. Scientists continue to debate whether cloud seeding in one region can have consequences for another. And at a time when droughts are becoming more common, rain is a precious commodity with geopolitical import. In recent years, Iran has accused the UAE and Israel, which has its own seeding experiments, of stealing rain away.

Reports that cloud seeding caused this week’s flooding were likely erroneous, but the reaction they inspired “represents a healthy kind of skepticism about what happens when we interfere with natural systems,” Laura Kuhl, a public-policy professor at Northeastern University who studies climate adaptation, told me. That’s particularly true, she said, when you consider forms of geoengineering premised on producing large-scale effects. Scientists have proposed injecting sulfur dioxide into the stratosphere to reflect some sunlight back into space, preventing it from reaching Earth’s surface. The resulting aerosols could linger in the stratosphere for years, shifting at the whims of the wind. Similar concerns surround another geoengineering technique that involves spraying salt compounds into the air to brighten clouds, which would in turn bounce sunlight back into space. This month, scientists conducted a secretive test of this technology, the first of its kind in the United States. The field is “moving a lot faster than it used to,” Juan Moreno-Cruz, a climate-policy researcher at the University of Waterloo, told me.

[Read: The very optimistic new argument for dimming the sky]

After further research, some geoengineering techniques may well turn out to be useful ways to mitigate or adapt to climate change. But they can’t address its root cause: the burning of fossil fuels, and failure to reduce greenhouse emissions. Many climate experts see geoengineering as a last resort. As our changing atmosphere continues to dramatically drench some parts of the planet and leave others parched for too long, that last resort might start to seem like a more appealing option—even as the consequences of getting it wrong become ever more dire.