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

熱波と干ばつによる不作、海水温上昇による漁獲不足

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

熱帯では深刻な飢餓が生じ、資源戦争により数百万人の難民が北へと逃げる

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

事態が急速に悪化する中、各国政府は緊急の対策を決定した…

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

このような悲惨なシナリオが実現するとは限らない

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

しかし気候変動に効果的に対処できなければ、絵空事でもない

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

近い将来、過激な対策が必要になりうる：ジオ・エンジニアリング（地球工学）だ

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

数世紀にわたる人類の負債が帳消しになるかもしれないし

climate change: Geoengineering.  Interventions so massive in scale  

悪化するかも

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

地球工学とはいったい？

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

有望な手段？　失敗したらどうなる？

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

ーイントロー

to seeding clouds with salt or  wilder ones like fertilizing  

地球工学は幅広く、宇宙に日傘、海水から雲といった空想的な手法から

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

海に鉄をまいて藻類を繁殖させるという荒っぽい手法まで様々だ

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

この動画では、私たちの存命中に取りうる選択肢に焦点をあてる

Stratospheric aerosol injection. A clunky term  

成層圏エアロゾル注入

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

成層圏に何かを散布して日射をさえぎるという意味の不格好な用語だ

Keeping the Sun away

日射をさえぎる

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

エネルギーはCO2自体からではなく、太陽から電磁波という形で供給されている。

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

約71％が地球表面と大気によって吸収され

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

そのエネルギーは、再び赤外線として放出される

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

CO2はこの赤外線を捉え、しばらく大気中に留める

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

この効果は、毛布の役割に似ていて

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

部屋が冷えていても身体は赤外線を放っており

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

内側の空気が赤外線を捉え、暖かさと快適さを生み出す

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

だから地球を冷やすには、毛布の内側にエネルギーが捉われないことが重要だ

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

それは自然にも行われる

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

地表に到達した日射の29％が宇宙へと反射されている

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

氷、砂漠、雪や雲といった光沢面によって

We can look at nature for inspiration:

反射が増えれば、エネルギーが減り、気温も下がる

Specifically the 1991 Mount Pinatubo  eruption, the second largest volcanic  

ヒントは自然現象で

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

特に1991年のピナツボ火山の噴火は

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

20世紀で2番目の規模だった

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

900人近い死者の一方、科学者は気候への世界的影響にも注目した。

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

噴火により何百万トンもの粒子とガスが成層圏まで放出され

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

しばらく滞留した

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

地球工学が注目したガスは二酸化硫黄だ

Global average temperatures dropped by 0.5°C.  

酷い匂いの透明なガス

It took three years until this  cooling effect had stopped.

大気の高くで硫酸の液滴となり、水と混ざって巨大なヴェールとなっていた

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

これにより地表に届く日射が約１％減少し

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

世界の平均気温が0.5℃低下した

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

この冷却効果は3年続いた

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

成層圏に硫黄粒子を注入すれば、その再現が可能だ

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

ある科学者によると、これは極めて容易で

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

新たな技術の開発すら必要ないという

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

ある研究によると、気候変動によるコストよりもかなり安価だ

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

年に一度、特注飛行機の小さな艦隊が空にのぼり

Unfortunately, there might be  a few unhappy side effects.

赤道にそってエアロゾルを散布し、世界中に拡散させる

There are a number of potential  issues with aerosol injections:  

年間5-8メガトンの散布で

rainfall patterns could change which  could negatively affect agriculture  

太陽光を反射して温暖化を減速、あるいは停止させ

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

化石燃料から脱却するための貴重な準備時間となる

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

残念ながら、いくつかの困った副作用がある

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

エアロゾルの投入にはいくつかの潜在的な問題があり

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

降雨パターンの変化は農業に悪影響を及ぼし、飢饉を起こしうる

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

最悪の場合、何十億という人々が影響を受ける

Scientists have already suggested  using a combination of different  

また1991年のピナツボ噴火では、

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

地表面が冷却だけでなく、成層圏の加温も生じ

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

オゾン層に悪影響を及ぼし、南極上空のオゾンホールは最大となった

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

硫黄粒子を数十年も注入すると、同じことが起こりうる

Politicians and industry  might use the cooling effect  

オゾン層への影響が小さいミネラルを組み合わせる提案もあるが

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

実効性の確認にはさらなる調査研究が必要だ

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

オゾン層を破壊しなくなっても、他のリスクもある

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

政治家や産業界が、脱炭素経済への転換を遅らせる口実にしかねない

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

地球工学で温暖化が緩和されても、人類がCO2を排出しつづければ

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

大気CO2が増加すれば、海洋のCO2吸収も増加し、酸性化する

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

すでにサンゴ礁のような巨大な生態系に致命傷を与えており

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

長引くほどに、影響も深刻となる

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

最悪なのは、一度大気へのエアロゾル散布を始めると

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

長期の継続を強いられ、終了時のリスクを抱えることになる

we are sitting on a time bomb.

つまり、人類がこのままCO2を排出しつつ

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

同時に太陽放射を妨げ温暖化を防ぐ戦略をとるなら

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

時限爆弾に座るようなものだ

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

地球工学をやめれば、以前の法則どおりに温暖化する

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

数十年にわたり冷却しつつも大量のCO2を排出してきた結果、

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

温暖化は極めて速やかに進行する

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

かつての50年分の温暖化が、10年で起こりうる

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

急速かつ大幅な温暖化は

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

あらゆる生態系をかく乱し、順応の時間を与えないだろう

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

最悪のシナリオは、劇的な飢餓と生態系の急速な破壊だ

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

人類は存続したとしても、見知らぬ困難な世界に住むことになる

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

最良のシナリオは、気候変動が人類存亡に関わると人類がやっと理解し

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

地球工学によって10～20年程度の時間が稼げる場合だ

# Conclusion

低炭素経済への移行や、大気中のCO2を減らすための時間、

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

今後紹介する予定の技術も利用されるかも

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

結論として

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

地球工学は危険な発想で

scientists from doing the experiments  necessary to understand it better.  

気候変動の解決策ではない

But blankly opposing  geoengineering is short sighted.

化石燃料の時代を引き延ばす口実にも使われかねない

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

ここ数十年、地球工学は激しい議論を呼び

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

多くの科学者が必要な実験すらできずにいた

This experiment is about to get really exciting.

しかし地球工学を全否定するのも短慮だろう

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

残念ながら、人類はすでに地球工学を実験している

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

毎年約400億トンのCO2を排出し、世界の劇的な変化を検証している

might accidentally press the self destruct button.

この実験は最高潮を迎えていて

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

幸いにもまだ地球工学の利用を強いられてはいない

on your science knowledge, just in case. Our  friends from Brilliant can help you with that.

もし必要な未来が来たなら

Brilliant is a problem-solving website and app  that makes science accessible in a practical  

科学的に解明しておくべきだ

way – more than 60 interactive courses give  you the tools to crack problems in math,  

備えあれば患いなし

logic and engineering all by yourself.  Instead of a classic lecture format  

さもないと、混乱した人類が自爆ボタンを押しかねない

Brilliant uses story-telling,  code-writing and hands-on problems  

（Brilliantの紹介）

to keep you entertained and engaged.  This way a small daily challenge can  

build up to real long-term understanding  of science and achieving your STEM goals.

In a nutshell, Brilliant surprises you and  keeps you on your toes, all while sneaking  

some knowledge into your head without your  really noticing – right up our alley, really.

To get a fresh perspective on science, go to  Brilliant.org/Nutshell and sign up free.  

And there’s an extra perk for kurzgesagt viewers:  

the first 200people to use the link  get 20% off their annual membership,  

which lets you view all the daily problems  in the archives and unlock every course.

Brillant helps you end your day  a little smarter – still the  

best preparation for the future we can think of.