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Hank talks about a few - maybe crazy, maybe reasonable - geoengineering schemes that some scientists have come up with in order to "fix" climate change, including designer clouds, ocean fertilization, and stratospheric shading with sulfur dioxide.

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Hank Green:  Humans are causing climate change and so some scientists say that it's our job to fix it.  Except not like cutting out all the fossil fuels.  That's just crazy talk.

[SciShow intro plays]

They're talking about geo-engineering, altering the atmosphere, the oceans, ice sheets and other parts of the world's climate systems to counteract the effects of global warming.  And these ideas, some of them, sound a little bit crazy.  Like sending a bunch of parasols into space to block the suns rays or covering ice sheets with blankets to insulate them from solar radiation.

But the question to me is if we're gonna have to do some of these things to like save the planet, what are the most realistic options for turning around climate change?  Well here are three maybe crazy, but maybe reasonable schemes to geo-engineer our way out of this mess.

(00:49) 1)  Designer clouds.  Many geo-engineers think that tinkering with clouds is our best option for helping with climate change, but different types of clouds have different effects on the climate.  For instance, high, wispy, cirrus clouds, which are made up of small, uniformly-sized ice crystals, let sunlight in while keeping infrared radiation from escaping our atmosphere.

So some geo-engineers want to use airliners to spray these trouble-making cirrus clouds with nice, inorganic crystalline compounds like bismuth tri-iodide for ice to stick to, making ice crystals grow larger, in turn causing them to sink and dissipate.  But while the high, icy cirrus clouds act as insulation, the bigger, whiter, fluffier clouds closer to the surface actually help reflect sunlight.

So another scheme calls for cloud whitening to bounce more of the solar energy back into space.  Whiter clouds are made of densely packed water droplets, so some geo-engineers want to send ships out into the ocean and have them spray sea water into the air.  Every droplet of sea water would contain tiny salt crystals, which the water vapor can then condense around, potentially creating new clouds while fluffing up and whitening existing ones.

The problem here, is that the size of the water droplets have to be just right: neither too small or too large, and cloud whitening could actually lead to less rainfall on a global scale.  It's kind of a problem of "Is the cure potentially worse than the disease?" but unfortunately we don't have a bunch of Earths to do clinical trials with.

(02:14) 2)  Fertilizing the oceans.  Geo-engineers also see an opportunity in marine phytoplankton, photosynthesizing algae in the ocean that consumes CO2 while providing a base for the marine food chain.  When they die, the plankton sink to the bottom of the ocean and their hard little shells smush together and eventually turn into rock, locking away all of that carbon inside of them.

So some geo-engineers are like, "What we need is more phytoplankton!"  And what phytoplankton really want is iron.  Artificially fertilizing the oceans with iron could theoretically create big blooms of algae that'll suck all the CO2 out of the air and then lock it away on the sea floor.

But this of course is also controversial.  When algae blooms decompose, they deplete the oxygen in the ocean, creating huge dead zones where fish and lots of other important stuff can't survive.  We know about this because farm runoff is already creating accidental algae blooms all over the world and they don't seem to be helping the climate any.

(03:05)  3)  Make yourself a shady stratosphere.  You know how sometimes a huge volcano spews a bunch of gas and dust into the stratosphere, reflecting sunlight and generally causing planet-wide mass extinctions?  Well some geo-engineers think that this can actually be a really good way of cooling the planet, but instead of like drilling into the ground and dropping a nuke down there or something, the plan calls for airplanes spraying out about 5 million tons of sulfur dioxide, the same compound spewed by volcanoes, into the stratosphere every year, I guess until we start to see results.

But what will the results really be?  Well we have climate models to guess for us.  Less sun could decrease annual rainfall over the whole globe because rain-clouds need the warmth from the sun.  Also, this strategy could cool the equator more than the poles and would change regional climates quite a bit even while keeping global temperatures down.

So, geo-engineers, you want crazy?  They got crazy.  But do they also have the key to survival on our planet?  Possibly.

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