Water vapour is a potent player in the Earth's greenhouse effect, serving as a critical amplifier that intensifies the warming of our planet. According to NASA, Earth's surface temperature would be about 59 degrees Fahrenheit (33 degrees Celsius) colder without the greenhouse gases. The greenhouse effect is a natural process that helps maintain Earth's temperature within a habitable range. But in recent years, the surface temperature has been rising because of human activities like burning of fossil fuels and deforestation, leading to global warming. Now, scientists have found a new way to cool an overheating earth - by reducing the amount of water vapour in the atmosphere.
According to a study published in Science Advances, researchers at the National Oceanic and Atmospheric Administration (NOAA) and NASA plan to inject ice high up in the air so that water vapour in the upper atmosphere would get a bit drier and that could counteract a small amount of the human-caused warmth.
The idea of drying the upper atmosphere is the newest addition to what some scientists are calling a last-ditch toolbox to deal with climate change by manipulating the world's atmosphere or oceans. Known as geoengineering, it's often rejected because of potential side effects, and is usually mentioned not as an alternative to reducing carbon pollution, but in addition to emission cuts.
"This isn't something that we can even implement right now. This is about exploring what might be possible in the future and identifying research directions," said Joshua Schwarz, a NOAA physicist who is lead author of the study.
Climate scientists plan to send high-tech planes to inject ice particles about 11 miles (17 kilometres) high, just below the stratosphere, where the air slowly rises. Then the ice and cold air rise to where it's coldest and gets the water vapour to turn to ice and fall, dehydrating the stratosphere.
However, Mr Schwarz said that there is no workable injection technique so far.
At its maximum, injecting 2 tons a week, it could conceivably take out enough water vapour to reduce heating a small amount, about five per cent of the overall warming created by carbon from the burning of fossil fuel. But the study added that it is not much and shouldn't be used as an alternative to cutting pollution.
The team is not quite sure about what side effects could occur, and that's the problem, other scientists said.
Purposely tinkering with Earth's atmosphere to fix climate change is likely to create cascading new problems, said University of Victoria climate scientist Andrew Weaver, who wasn't part of the study. He said the engineering side of this makes sense, but he compared the concept to a children's story where a king who loves cheese is overrun with mice, gets cats to deal with the mice, then dogs to chase away the cats, lions to get rid of the dogs and elephants to eliminate the lions and then goes back to mice to scare off the elephants.
Water vapour is also classified as a greenhouse gas, which is most abundant in the atmosphere, but according to NASA, it is not the main driver of Earth's current warming. Instead, it's a consequence of it.
The space agency has explained how water vapour amplifies the warming caused by other greenhouse gases like carbon dioxide (CO2) and methane.
Water vapour is generated when the amount of methane and CO2 go up in the atmosphere, which leads to increased evaporation. Since warmer air holds more moisture, its concentration of water vapour increases. Specifically, this happens because water vapour does not condense and precipitate out of the atmosphere as easily at higher temperatures, said NASA.
The water vapour then absorbs heat radiated from Earth and prevents it from escaping out to space. This further warms the atmosphere, resulting in even more water vapour in the atmosphere - something the agency dubbed as a "positive feedback loop".
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