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April 8\u2019s North American solar eclipse is just around the corner, and it has astronomy fans and weather aficionados alike preparing for an incredible show. But it\u2019s not just fun and games. Eclipses are rare opportunities for scientists to study phenomena that only come around once in a while.<\/p>\n
Last week, a team of meteorological experts from the Netherlands released a paper describing how eclipses can disrupt the formation of certain types of clouds. Their findings have implications for futuristic geoengineering schemes that propose to artificially block sunlight to combat climate change.<\/p>\n
<\/p>\n Published in Nature Communications Earth & Environment<\/em>, the paper examines satellite imagery of cloud cover during three solar eclipses between 2005 and 2016.<\/p>\n They found that in the wake of an eclipse, shallow cumulus clouds tend to disappear \u2013 and it doesn\u2019t even need to be a total eclipse for this to occur \u2013 it happens when just 15% of the Sun is obscured.<\/p>\n The effect isn\u2019t immediate. There\u2019s a delay of about 20 minutes. That\u2019s because the eclipse isn\u2019t destroying the clouds directly. Instead, it\u2019s cooling the land beneath, interrupting packets of warm air that race upwards in updrafts to condense into clouds. By suppressing the updrafts, the eclipse puts a pause on cumulus cloud formation.<\/p>\n Proposals to reduce climate change by artificially blocking the Sun work on a similar principle to an eclipse. A swarm of sun-shade spacecraft, or an injection of light-absorbing aerosols into the atmosphere, could reduce the amount of solar energy reaching the surface of the Earth, cooling the temperature back to historical norms. For a project like this to work, about 3.5% to 5% of sunlight would have to be blocked.<\/p>\n The cloud modeling data from this paper indicates reasons to be cautious, however. First and foremost, it suggests that blocking sunlight isn\u2019t as effective as you might think, because while it does cool the ground initially, it also reduces cloud cover, which once again increases the amount of solar energy reaching the Earth.<\/p>\n The decrease in cloud cover would also have an effect on precipitation \u2013 fewer clouds means less rain \u2013 which might result in regional increases in drought and desertification.<\/p>\n It\u2019s unclear whether the reduction in cumulus clouds would persist with a more permanent, artificially constructed eclipse \u2013 true solar eclipses only last a few minutes locally, after all. But the authors say the data ought to influence the design of any serious geoengineering proposals going forward. A solar shade stationed between the Sun and Earth, at Lagrange point 1, for example, might not block the Sun uniformly. If it caused either partial or intermittent local eclipses, it would be more likely to feature these cloud-destroying effects.<\/p>\n Atmospheric aerosol injection might seem like a more uniform method of blocking sunlight, but large-scale weather patterns actually make these methods potentially even more variable, blocking up to 45% of sunlight locally on occasion (well beyond the 15% needed to see a reduction in cloud formation).<\/p>\n These geoengineering projects, in other words, might solve climate change only to introduce new, unexpected challenges, and the costs might not be borne equitably across the globe.<\/p>\n So what\u2019s the lesson? Well, if you\u2019re going out to see the eclipse on April 8, and you feel a little chill in the air, you\u2019re not imagining it. The Earth around you is cooling \u2013 and it might also get a little sunnier after it\u2019s over, as cumulus cloud formation gets interrupted. These effects are tangible reminders that the relationship between Earth\u2019s climate and the Sun is complex \u2013 and tinkering with it comes with a high chance of unintended consequences.<\/p>\n Read the Paper:<\/strong><\/p>\n Victor Trees et al. \u201cClouds dissipate quickly during solar eclipses as the land surface cools.\u201d Communications Earth and Environment<\/em>. February 12, 2024.<\/p>\nLike this:<\/h3>\n