Decades of heatwaves and droughts  have led to unusually poor harvests,  

while the warming oceans yield fewer fish each  year. In the tropical zones, millions suffer from  

famine and resource wars have made millions  more flee to the north. As things quickly  

get worse, in an act of desperation, the world's  governments decide to enact an emergency plan...

It is far from certain that a grim scenario like  this will play out. But the failure of world  

leaders to effectively address climate  change, makes it far from impossible.

So in the near future it might become necessary  to try something radical to slow down rapid  

climate change: Geoengineering.  Interventions so massive in scale  

that they might undo centuries of human  behavior. Or make everything much worse.

What is geoengineering, is it really  an option and what if it goes wrong?

Geoengineering methods vary from fantastic ones  like constructing giant light sails in space  

to seeding clouds with salt or  wilder ones like fertilizing  

the oceans with iron to speed up the  growth of trillions of algae cells.

In this video we’ll focus on an intervention  we could see during our lifetimes:  

Stratospheric aerosol injection. A clunky term  

that means spraying stuff very high up  in the atmosphere to keep the sun away.

Keeping the Sun away

CO2 doesn’t heat up the planet on its own, almost  all of the energy on earth comes from the sun in  

the form of electromagnetic radiation. About 71%  of this energy is absorbed by the earth's surface  

and atmosphere. This absorbed energy is  emitted again, as infrared radiation. And  

CO2 is able to trap this infrared radiation  and keep it in the atmosphere for a while.  

You can compare this effect with  snuggling under a blanket in the morning.  

Even in a really cold room, your  body emits infrared radiation  

and the air between your body and the blanket  traps it and creates a warm and comfy feeling.

So one way to cool down the planet would  be to prevent energy from getting trapped  

under our planet blanket. Which is  already happening naturally. About 29%  

of the solar radiation hitting earth  is reflected back to space by bright  

surfaces like ice, deserts, snow or clouds.  More reflection, less energy, less warming.

We can look at nature for inspiration:

Specifically the 1991 Mount Pinatubo  eruption, the second largest volcanic  

eruption of the 20th century. Aside from  massive devastation and almost 900 dead,  

scientists noted its strong impact on the  global climate. The explosion ejected millions  

of tons of particles and gas as high as the  stratosphere which hung around there for a while.

The stuff that is interesting for geoengineering  is sulphur dioxide. A nasty smelling and invisible  

gas. High in the atmosphere, it produced a haze  of sulfuric acid droplets, that mixed with water  

and created giant veils. These veils reduced the  sunlight reaching earth’s surface by roughly 1%.  

Global average temperatures dropped by 0.5°C.  

It took three years until this  cooling effect had stopped.

Humans could imitate this process by injecting  sulfur particles directly into the stratosphere.  

According to some scientists, this  might be surprisingly easy to do  

and we don’t even need a lot of new  technology for it. According to one study,  

it also might be pretty cheap compared  with the cost of rapid climate change.

A small fleet of specialized airplanes could  ascend once a year and distribute aerosols along  

the equator from where they would be spread around  the world. Projections assume that injecting  

between five and eight megatons of material per  year would reflect enough sunlight to slow down  

or even stop global warming. . Giving us precious  time to transition away from fossil fuels.

Unfortunately, there might be  a few unhappy side effects.

There are a number of potential  issues with aerosol injections:  

rainfall patterns could change which  could negatively affect agriculture  

and cause famine. Billions of people  could be affected in the worst case.

Also, after the 1991 Mount Pinatubo eruption, the  acid/water veils not only cooled down the surface,  

they also heated up the  stratosphere. As it turns out,  

acid is bad for the ozone layer and the  ozone hole over Antarctica was the largest  

it ever has been . Injecting sulfur particles  over decades could have a similar effect.

Scientists have already suggested  using a combination of different  

minerals that might have much less  harmful effects on the ozone layer  

but more research and experiments need  to be done to make sure this could work.

But even if we don’t damage the  ozone layer, there are other risks.

Politicians and industry  might use the cooling effect  

as an excuse to delay the switch  to a carbon neutral economy.

Even if geoengineering slows down global  warming, humanity is still adding extra CO2  

to the atmosphere. More CO2 in the air means  that the oceans absorb more CO2, which makes  

them more acidic. This is already beginning to  be deadly to huge ecosystems like coral reefs.  

And the longer this continues, the  more severe the effects will be.

But it gets worse: Once we start pumping  particles into the atmosphere on a massive scale,  

we might be forced to do so for a long  time, or we could risk a termination shock.

What that means is that if humanity  continues to enrich the atmosphere with CO2,  

but at the same time prevents the planet  from heating up by blocking solar radiation,  

we are sitting on a time bomb.

Once we stop geoengineering, the  natural cycle will take over again,  

and earth would heat up. But after a few  decades of keeping the planet artificially  

cold while still releasing massive amounts of  CO2, it would heat up, much, much quicker. An  

increase in temperature that would take 50  years today, could happen in just 10 years.

Such a temperature shock in such  a short time would disrupt every  

major system on earth so much that it  would be impossible to adapt in time.  

The worst case scenario could be dramatic  famines and the rapid destruction of ecosystems.

Humanity might survive. But the survivors would inhabit an unfamiliar and hostile world.

The best case scenario is that once the world has  finally fully understood the existential danger  

of rapid climate change,geoengineering  can buy us a crucial decade or two.  

Time to transition our economies  and maybe even pull CO2 out of the  

atmosphere. Maybe with technologies  that we’ll discuss in a future video.

# Conclusion

Geoengineering is a scary concept. It is not a  solution to climate change and it might even be  

a welcome excuse for the fossil fuel industry  to delay the end of the fossil fuel age.

Over the last few decades geoengineering has  been so controversial that it stopped many  

scientists from doing the experiments  necessary to understand it better.  

But blankly opposing  geoengineering is short sighted.

The sad truth is that we are already  running a geoengineering experiment.  

We are testing how fast the world changes if  we add about 40 billion tons of CO2 each year.  

This experiment is about to get really exciting.

Hopefully we never have to use Geoengineering.  But if we need to in the future,  

we better have done the science. We better  be prepared. Or a panicking humanity  

might accidentally press the self destruct button.

You probably won’t have to do any of that  yourself – but who knows! Better brush up  

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