[00:00.00]Narrator：Listen to part of a lecture in an environmental engineering class.[00:09.49]Professor:Today, I’d like to discuss a branch of environmental engineering called geo-engineering.[00:16.07] The main goal of geo-engineering is to control global warming, to counteract the warming effect of emissions of greenhouse gases are causing. Greenhouse gases make it more difficult for Earth to radiate heat energy into space.[00:34.21] So to counteract this effect, geo-engineers are trying to come up with ideas to reflect more of the sun’s radiation back into space. Not all ideas seem realistic, but one stands out as a possibility.[00:50.99] And that’s clouds brightening. You see, we know that clouds are already great reflectors of sunlight so making them even more effective make sense, right? Well, that’s what cloud brightening means to accomplish.[01:06.49] It’s believed that spraying clouds with sea water mist may increase the density of clouds in the air, making them brighter. Why sea water mist? Jonathan?
[01:18.77]Jonathan:Because sea water maintains salt? [01:21.85]Professor:Exactly. The assumption made is that the mist would dry out, leaving salt particles behind. The water vapor in the cloud would then condense on these salt particles, forming denser clouds.[01:36.11] The whole theory is that the salt particles will be more efficient at attracting water vapors than existing particles in the atmosphere over the open ocean.[01:47.22] And this would make the clouds brighter, which in turn would increase their reflectivity.
[01:53.20]Female:But how would they do that? I mean, spraying clouds with sea water.[01:58.42]Professor:Engineers have thought about how they could spray this mist into the air and came up with an idea for ships called albedle yacht.[02:07.34] Now, remember albedle is the term for the reflective power of the surface to a body, such as a cloud. Basically, these albedle yachts would be set out to the ocean to create sea water mist.[02:21.77] They’d be remote controlled and wind powered. They wouldn’t use traditional sails, instead they’d use Flattner rotors.
[02:30.90]Flattner rotors are tall tubes that spin in the wind, causing the ship to move perpendicular to the wind. It’s a proven technology.[02:41.35] These spinning tubes can be powered by just wind but unlike conventional sails, these tubes won’t get damaged by strong wind. Also, a seawater spout system could be installed inside these tubes.[02:56.96] And that would spray saltwater droplets into the atmosphere as the tubes spin. Now, as promising as the albedo yacht might sound, this idea does have its obstacles.[03:10.34] Probably the biggest problem is how to design the system to create the spray. You see, these droplets that will be set up to the clouds need to be very small.[03:22.54] In order to attract a lot of water vapor, each droplet can’t be more than two microns across. In case you’re wondering, two microns is about the size of bacteria and that’s not all.[03:36.58] These droplets all have to be the same size so that they won’t clump together. If they do, then that might result in rain, making the cloud dissipate which is the opposite of what we want.[03:50.43] We want the clouds to get bigger, not smaller.
[03:54.29]One idea is to force water through tiny holes, like a watering can. The only problem with this is that it would require drilling 1.5 billion tiny holes in some material for this to work.[04:09.55] Engineers could use silicon, which has been used in micro-electronics for many years, since there’s a track record of creating tiny devices like computer chips with silicon, they figure it could be the appropriate material for tiny holes.[04:25.74] But experiments have shown that more problems need to be solved before going forward, such as how to prevent these holes from clogging.
[04:36.01]Male:But when all these problems are ironed out, is it going to work?[04:40.30]Professor:Well, cloud brightening might be the most promising technique so far. But there’s nothing that says it will definitely work. And even if it did work to some extent, who knows what’s going to happen?[04:54.06] Making these bigger clouds could backfire and cause less rainfall in some places and it could cause ocean currents to change.[05:02.95] We don’t even know if these particles could have a negative effect on the ozone layer so there are potential dangers on the global scale.
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