The Montreal Protocol proved that the world could come together and take action on climate change. Thirty years after the world’s most successful environmental treaty was signed, atmospheric scientist Sean Davis examines the world we avoided when we banned chlorofluorocarbons — and shares lessons we can carry forward to address the climate crisis in our time.


世界で最も成功した環境条約が締結されてから 30 年後、大気科学者のショーン・デイビスは、クロロフルオロカーボンを禁止したときに私たちが避けてきた世界を検証し、現代の気候危機に対処するために私たちが引き継ぐことができる教訓を共有します。

タイトル Can we solve global warming? Lessons from how we protected the ozone layer
アップロード 2019年2月13日
キャスト ショーン・デイビス

「Can we solve global warming? Lessons from how we protected the ozone layer(地球温暖化は解決できるのでしょうか?オゾン層の保護方法から得た教訓)」の文字起こし



  • 多くの人が気候変動についての科学的情報を信頼していない。


  • 1970年代にクロロフルオロカーボン(CFC)がオゾン層を破壊していることが判明。CFCはエアロゾルスプレーや冷蔵技術に使われていた。
  • オゾン層は地球のサンスクリーンで、太陽の有害な紫外線を90%以上遮断している。


  • 1985年に南極でオゾンホールが発見され、1987年にモントリオール議定書が採択された。これはオゾン層を破壊する物質を削減するための国際協定で、地球温暖化を遅らせる効果もあった。


  1. 絶対的な確実性は必要ない:リスク管理には不確実性が伴うが、それでも行動することが重要。
  2. 協力が必要:環境問題の解決には、産業界、政府、環境保護団体、科学者、市民など、すべてのステークホルダーの協力が必要。
  3. 完璧を求めすぎない:小さな行動や不完全な取り組みでも、積み重ねることで大きな成果が得られる。


  • モントリオール議定書の成功を踏まえ、気候変動に対しても積極的に行動する必要がある。将来の世代が避けた世界を祝えるように、今から行動を始めることが重要。


So, I’m a climate scientist, and if this room is representative of the country we live in, that means about 60 percent of you, so maybe from about there over, don’t strongly trust me for information on the causes of climate change.


Now, I promise to tell the truth tonight, but just to humor that demographic, I’ve started this talk with a falsehood.

[The Paris Climate Accord is a product of the recognition that climate change is a global problem …] This statement was not made by President Obama. It was made by President Reagan, and it wasn’t about climate change and the Paris Climate Accord. It was actually about the Montreal Protocol and stratospheric ozone depletion.

Now, I’m sure that many of you aren’t familiar with this environmental problem, but you should be, because it’s a rare environmental success story. And it’s worth revisiting, because sometimes, we need to examine the world we’ve avoided in order to find guidance for the choices we make today.

**What is the ozone layer**

So let’s go back to the 1970s, when some questionable choices were made: first of all — hoo — hairstyles. (Laughs) Second of all, objectively terrible quantities of hairspray, and third, CFCs, chlorofluorocarbons, man-made chemicals that were used as propellant in aerosol spray cans. And see, it turns out these CFCs were a problem because they were destroying the ozone layer.

Now I’m sure most of you have heard of the ozone layer, but why does it matter? Well, quite simply, the ozone layer is earth’s sunscreen, and it’s really fragile. If you could take all of the ozone, which is mostly about 10 to 20 miles up above our heads, and compress it down to the surface of the earth, it would form a thin shell only about two pennies thick, about an eighth of an inch. And that thin shell does an amazing amount of work, though. It filters out more than 90 percent of the harmful UV radiation coming from the sun.

And while I’m sure many of you enjoy that suntan that you get from the remaining 10 percent, it causes a lot of problems: cataracts, damage to crops, damage to immune systems and also skin cancer. It’s not an exaggeration to say that a threat to the ozone layer is a threat to human safety.

And actually, ironically, it was human safety that motivated the invention of CFCs in the first place. You see, in the early days of refrigeration, refrigerators used toxic and flammable chemicals like propane and ammonia. For good reason, the refrigeration industry wanted a safe alternative, and they found that in 1928, when a scientist named Thomas Midgley synthesized the first commercially viable CFCs. And in fact, Midgley famously inhaled CFCs and blew out a candle to demonstrate, at a scientific conference, that they were safe and nonflammable.

And in fact, as a scientist, I can tell you there is no way you could get away with that kind of antic today. I mean, wow. But really, at the time, CFCs were a really remarkable invention. They allowed what we now know as modern-day refrigeration and air-conditioning and other things.

**CFC ban**

So it wasn’t actually until over 40 years later, in the 1970s, when scientists realized that CFCs would break down high in the atmosphere and damage the ozone layer. And this finding really set off a lot of public concern. It led, ultimately, to the banning of CFC usage in aerosol spray cans in the US and a few other countries in 1978.

Now, the story doesn’t end there, because CFCs were used in much more than just spray cans. In 1985, scientists discovered the Antarctic ozone hole, and this was a truly alarming discovery. Scientists did not expect this at all.

**Antarctic ozone hole**

Before the Antarctic ozone hole, scientists expected maybe a five or 10 percent reduction in ozone over a century. But what they found over the course of less than a decade was that more than a third of the ozone had simply vanished, over an area larger than the size of the US. And although we now know that CFCs are the root cause of this ozone hole, at the time, the science was far from settled. Yet despite this uncertainty, the crisis helped spur nations to act.

**Montreal Protocol**

So that quote that I started this talk with, about the Montreal Protocol, from President Reagan — that was his signing statement when he signed the Montreal Protocol after its unanimous ratification by the US Senate. And this is something that’s truly worth celebrating. In fact, yesterday was the 30th anniversary of the Montreal Protocol.


Because of the protocol, ozone-depleting substances are now declining in our atmosphere, and we’re starting to see the first signs of healing in the ozone layer. And furthermore, because many of those ozone-depleting substances are also very potent greenhouse gases, the Montreal Protocol has actually delayed global warming by more than a decade. That’s just wonderful.

But I think it’s worth asking the question,

**Lessons from Montreal**

as we face our current environmental crisis, global warming, what lessons can we learn from Montreal? Are there any? I think there are. First, we don’t need absolute certainty to act. When Montreal was signed, we were less certain then of the risks from CFCs than we are now of the risks from greenhouse gas emissions.

A common tactic that people who oppose climate action use is to completely ignore risk and focus only on uncertainty. But so what about uncertainty? We make decisions in the face of uncertainty all the time, literally all the time. You know, I’ll bet those of you who drove here tonight, you probably wore your seat belt. And so ask yourself, did you wear your seat belt because someone told you with a hundred percent certainty that you would get in a car crash on the way here? Probably not. So that’s the first lesson. Risk management and decision making always have uncertainty. Ignoring risk and focusing only on uncertainty is a distraction.

**It takes a village**

In other words, inaction is an action. Second, it takes a village to raise a healthy environment. The Montreal Protocol wasn’t just put together by industry and governments or environmental advocacy groups and scientists. It was put together by all of them. They all had a seat at the table, and they all played an important role in the solution.

And I think in this regard, we’re actually seeing some encouraging signs today. We see not just environmental groups concerned about climate change but also civic and religious groups, the military and businesses. So wherever you find yourself on that spectrum, we need you at the table, because if we’re going to solve global warming, it’s going to take actions at all levels, from the individual to the international and everything in between.

**Don’t let the perfect be the enemy**

Third lesson: don’t let the perfect be the enemy of the good. While Montreal has become the brake pedal for stopping ozone depletion, at its beginning, it was more just like a tap on the brakes. It was actually the later amendments to the protocol that really marked the decision to hit the brakes on ozone depletion.

So to those who despair that the Paris Climate Accord didn’t go far enough or that your limited actions on their own won’t solve global warming, I say don’t let the perfect be the enemy of the good.

**The world we’ve avoided**

And finally, I think it helps us to contemplate the world we’ve avoided. Indeed, the world we have avoided by enacting the Montreal Protocol is one of catastrophic changes to our environment and to human well-being. By the 2030s, we’ll be avoiding millions of new skin cancer cases per year with a number that would only grow. If I’m lucky, I’ll live long enough to see the end of this animation and to see the ozone hole restored to its natural state. So as we write the story for earth’s climate future for this century and beyond, we need to ask ourselves, what will our actions be so that someone can stand on this stage in 30 or 50 or a hundred years to celebrate the world that they’ve avoided.

Thank you.