Scientists are considering taking risks to cool down the Earth.

Rising moist air forms towering storm clouds. When it comes to greenhouse gases, people usually think of carbon dioxide and methane. However, they often overlook ordinary water vapor, which is actually a major greenhouse gas. Water vapor can linger in the stratosphere for years, enhancing the greenhouse effect by absorbing solar radiation and reacting with other gases. According to a study, the upward motion of water vapor in the stratosphere during the 1990s may have contributed to a 30% increase in global warming during that period. But what would happen if we could prevent water vapor from reaching the stratosphere at its source? Based on this idea, a new technology called "stratospheric dehydration" has emerged. In a study published on February 28th in Science Advances, researchers propose injecting cloud condensation nuclei into moist rising air streams before they enter the stratosphere, effectively "dehydrating" the stratosphere. "Keeping the stratosphere dry may only require the weekly injection of 2 kilograms of material," says Shuka Schwarz, the lead author of the study and a physicist at the National Oceanic and Atmospheric Administration (NOAA) Chemical Sciences Laboratory. This stratospheric dehydration measure can moderately reduce temperatures and offset 1.4% of global warming caused by the rise in carbon dioxide over the past few centuries. The key to implementing this technology lies in the fact that there are only a few places in the world where the atmospheric conditions are sufficient to generate strong updrafts that transport air into the stratosphere, occurring primarily at specific latitudes. One of the most important of these "entry points" is located above the western equatorial Pacific, which is equivalent in size to Australia. During the process of air ascent, most of the water vapor condenses into clouds and produces precipitation. However, observations conducted by NASA over the past decade beneath the stratosphere discovered that there is enough moist air mass capable of cloud formation, but it lacks the particles needed for water condensation into ice crystals and subsequent rain formation. "This is a question about opportunity - whether the air can reach the coldest regions of its journey and whether there are enough cloud condensation nuclei to do the job," Schwarz explains. NASA's research also found that these moist air masses are concentrated, with just 1% of the investigated masses carrying half of the total moisture that eventually reaches the stratosphere. As a result, the research team simulated the outcome of injecting bismuth triiodide as a condensation nucleus into the 1% most suitable water-collection area. The study shows that, in an optimistic scenario, injecting 2 kilograms of 10-nanometer diameter condensation nuclei per week would be sufficient to transform these moist air masses into clouds. This amount of material could be delivered using balloons or drones, eliminating the need for aircraft. However, many experts approach this idea with caution. Atmospheric chemist Daniel Cziczo from Purdue University in the United States comments that while the concept is interesting, it may carry risks. For example, if the condensation nuclei fail to form clouds in the correct location or disperse elsewhere, it could accelerate the formation of unintended cloud types, consequently causing a warming effect rather than cooling. "Nevertheless, for those geoengineers who have discussed cooling the Earth by injecting thousands of tons of reflective particles into the stratosphere, this certainly represents a potentially viable new idea," says Ulrike Lohmann, an atmospheric physicist from the Swiss Federal Institute of Technology Zurich. "It's a feasible approach." Related Paper Details: https://doi.org/10.1126/sciadv.adk0593 Please scan the QR code below for 3 seconds to recognize.Global warmingcloud condensation nucleistratospherestratospheric dehydration measuresreflective particlesclimate engineeringresearch.