Bold ideas to cool the planet | BBC Ideas

0:00 Can we reflect away the sun's rays to slow down climate change?

0:04 Let's find out.

0:05 The planet is warming up faster than

0:07 at any point in the Earth's recorded history.

0:10 Today, about a third of the world's electricity comes from renewable sources,

0:14 but fossil fuels are still driving dangerous levels of greenhouse gas emissions.

0:19 These act as a blanket, trapping the sun's heat,

0:22 with carbon dioxide doing most of the damage.

0:25 There's now more CO2 in our atmosphere than there has

0:27 been at any time in the last 3 million years.

0:30 So scientists are now urgently looking for ways to slow down climate change,

0:35 primarily to buy us some time to cut back on those emissions.

0:41 Solar radiation modification, basically reflecting the sun's heat energy back

0:45 into space is one of these ideas.

0:47 Or actually, there's a few options being

0:50 considered and some are definitely better than others.

0:54 So firstly, why not just put giant mirrors

0:57 in space and bounce the sun's rays away?

0:59 We know for certain that mirrors reflect light.

1:02 So that side of things is possible.

1:04 But here's the catch.

1:05 Or rather, the catch is it would cost trillions of dollars.

1:09 It would take decades to build.

1:12 And according to scientists,

1:13 you'd need a mirror three times the size of Egypt to make a difference.

1:17 Okay, so can we do something here on the ground to reflect more sunlight?

1:22 Well, there are various ideas for increasing

1:24 the Earth's surface reflectivity or albido effect,

1:28 like developing more reflective crops, painting rooftops white,

1:32 or covering areas with reflective materials.

1:35 There's some evidence that this could help cool local temperatures,

1:39 for example, a street or a neighborhood.

1:42 But these areas are just too small to make

1:46 any significant difference to the climate at a global level.

1:49 Making things more reflective sounds like a good idea,

1:52 but whatever it is would need to be huge.

1:55 What's huge and just hanging out in the sky already?

1:59 Clouds.

2:00 This is where things get really interesting.

2:03 One idea scientists are exploring is called marine cloud brightening.

2:07 The idea is basically for ships to spray fine

2:10 sea salt particles into the lowest part of the atmosphere.

2:14 Each particle acting like a mini mirror reflecting sunlight away from the Earth.

2:19 Early research suggests that this could work.

2:21 However, there are still many uncertainties.

2:23 The particles would need constant replenishing and the scale would be enormous

2:28 and there is a risk that clouds might darken rather than brighten,

2:33 reducing the cooling effect.

2:34 Also, even if you cooled down one area, it could trigger weather somewhere else.

2:39 Any other ideas?

2:40 Yes.

2:41 Taking inspiration from volcanoes,

2:43 this one's called stratospheric aerosol injection.

2:46 The idea is to release tiny particles called aerosols high up in the atmosphere.

2:53 These particles would mimic the effect of explosive volcanic eruptions,

2:58 reflecting sunlight back into space and cooling the planet below.

3:01 And we have a good idea that this can work because nature's already done it.

3:06 In 1991, the eruption of Mount Pinatubo in the Philippines

3:10 injected huge amounts of sulfur dioxide into the stratosphere.

3:14 These particles spread around the world in weeks and cooled

3:17 global temperatures by 0.3° C for a few years.

3:21 Scientists say there is good evidence that stratospheric aerosol

3:24 injection would work if done in the right way.

3:27 But here's the problem.

3:28 Aerosols in the stratosphere don't last.

3:31 To create long-term cooling, they would need to be continuously replenished.

3:36 And how would we even get material that high?

3:39 In theory, existing technologies like high

3:42 altitude aircraft or balloons could be adapted.

3:45 But to cool the planet, even just by one degree Celsius,

3:49 scientists estimate it could take roughly 1,800 flights every single day,

3:53 each carrying 15 tons of aerosol payloads.

3:57 So, where does all of this leave us?

4:00 Ideas like marine cloud brightening

4:03 or stratospheric aerosol injection may well work,

4:06 potentially reducing global temperatures and extreme weather events.

4:09 And this could hold back climate change for a time.

4:13 But these ideas come with real risks.

4:16 Studies have shown that if used in the wrong way or in the wrong hands,

4:21 they could change largecale weather patterns,

4:24 warming the polar regions rather than cooling them,

4:27 and altering rainfall around the world.

4:29 While global average temperatures may be reduced,

4:32 the weather or climate in certain regions of the world could get worse.

4:36 For instance, causing winter droughts over the Mediterranean

4:39 or the dieback of the Amazon rainforest.

4:42 None of these ideas are a substitute for cutting emissions,

4:47 the only shorefire way to slow down climate change.

4:50 The fact that scientists are even considering these huge, expensive,

4:55 complex options shows the jeopardy we're

4:57 in in terms of slowing down climate change.

5:01 Perhaps the most powerful reflection we can make is on ourselves.

5:05 Thanks for watching.

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