I think this is the, this is the moral hazard question, David.

Yeah.

So, um, I'm doing the best I can, which is not that much, is the answer.

So maybe I'm doing less than I used to in the sense that when I was at Calgary earlier in my career, I was more kind of directly fighting against the fossil fuel powers.

I mean, broadly, I've tried to speak to political elites and environmental elites about climate dangers forever, and I've tried to point directly to the, um, political power of the fossil fuel world.

Um, maybe it's helpful to say on a personal note that I've actually really had this up close and personal while I was a professor at Calgary.

One time I had a full-page ad taken out against me by the so-called Friends of Science, uh, and I've been part of a confrontation about the oil patch at University of Calgary that actually is part of what led to me going and confronting the president on the n-national CBC broadcaster.

He says, "In tackling climate change with a techno tweak, unless we tackle economic growth, we won't deal with the resource use, waste, and pollution with resulting environmental and quality-of-life impacts." That's more of a statement than a question, but I'd like you to respond to it.

This idea that we're sort of custodians of this amazing, unique planet and that we have intervened to change it [chuckles] and that we need to start looking after it.

Yeah.

A- A- Absolutely.

I think-- I mean, j- go kind of back and forth between the technical and the, and the, the ethical.

A thing that we haven't quite said yet is that the most important probably single thing to know about climate change is that warming is proportional to the cumulative emissions of carbon dioxide.

So that means that e- even if we stopped carbon dioxide emissions, which is absolutely doable, and we're making progress to it, but it's immensely hard to do.

We have to, you know, we have to change the engines on the plane while it's flying.

So, so could we get down to, like, practical propositions? What is your proposition that, that should happen now? How much sulfur should be sprayed into the atmosphere, and, and crucially, what effect would that have, uh, on global temperatures?

When sulfur dioxide is released into the atmosphere, it reacts with water vapor to become sulfuric acid.

Which is both naturally put in the stratosphere and also put in the stratosphere by our pollution.

So the w- way to do sunlight reflection that's most studied and best understood and most technically possible in the sense that we could start basically now is putting sulfuric acid droplets of aerosols into the stratosphere.

And why the stratosphere? That's because, uh, materials stay in the stratosphere for about two years, whereas if you put aerosols in the lower atmosphere from, say, a, a pollution source, they just stay for about a week before they fall back to Earth.

What happens when they do eventually fall back to Earth? How, uh, dangerous is it?

So, so, um, it is dangerous, but the good thing about it is we know a lot about what that danger is, and we can quantify it, and the reason is that, uh, sulfate aerosols are perhaps humanity's worst environmental pollutant of all time, literally.

So, um, overall human history, something more than a hundred million people have been killed by sulfate aerosol air pollution, and people have known that it's a toxic danger for a very long time.

The first, um, formal regulation of, of it was a proclamation that the King of London made to stop burning what were high sulfur sea coals in the year nine hundred.

When sulfur dioxide is released into the atmosphere, it reacts with water vapor to become sulfuric acid.

Which is both naturally put in the stratosphere and also put in the stratosphere by our pollution.

So the w- way to do sunlight reflection that's most studied and best understood and most technically possible in the sense that we could start basically now is putting sulfuric acid droplets of aerosols into the stratosphere.

And why the stratosphere? That's because, uh, materials stay in the stratosphere for about two years, whereas if you put aerosols in the lower atmosphere from, say, a, a pollution source, they just stay for about a week before they fall back to Earth.

What happens when they do eventually fall back to Earth? How, uh, dangerous is it?

So, so, um, it is dangerous, but the good thing about it is we know a lot about what that danger is, and we can quantify it, and the reason is that, uh, sulfate aerosols are perhaps humanity's worst environmental pollutant of all time, literally.

So, um, overall human history, something more than 100 million people have been killed by sulfate aerosol air pollution, and people have known that it's a toxic danger for a very long time.

The first, um, formal regulation of, of it was a proclamation that the King of London made to stop burning what were high sulfur sea coals in the year 900.

When sulfur dioxide is released into the atmosphere, it reacts with water vapor to become sulfuric acid.

Which is both naturally put in the stratosphere and also put in the stratosphere by our pollution.

So the way to do sunlight reflection that's most studied and best understood and most technically possible, in the sense that we could start basically now, is putting sulfuric acid droplets of aerosols into the stratosphere.

And why the stratosphere? That's because, uh, materials stay in the stratosphere for about two years, whereas if you put aerosols in the lower atmosphere from, say, a, a pollution source, they just stay for about a week before they fall back to Earth.

What happens when they do eventually fall back to Earth? How, uh, dangerous is it?

So, so, um, it is dangerous, but the good thing about it is we know a lot about what that danger is, and we can quantify it.

And the reason is that, uh, sulfate aerosols are perhaps humanity's worst environmental pollutant of all time, literally.

So, um, overall human history, something more than a hundred million people have been killed by sulfate aerosol air pollution.

When sulfur dioxide is released into the atmosphere, it reacts with water vapor to become sulfuric acid.

Which is both naturally put in the stratosphere and also put in the stratosphere by our pollution.

So the way to do sunlight reflection that's most studied and best understood and most technically possible, in the sense that we could start basically now, is putting sulfuric acid droplets of aerosols into the stratosphere.

And why the stratosphere? That's because, uh, materials stay in the stratosphere for about two years, whereas if you put aerosols in the lower atmosphere from, say, a, a pollution source, they just stay for about a week before they fall back to Earth.

What happens when they do eventually fall back to Earth? How, uh, dangerous is it?

So, so, um, it is dangerous, but the good thing about it is we know a lot about what that danger is, and we can quantify it.

And the reason is that, uh, sulfate aerosols are perhaps humanity's worst environmental pollutant of all time, literally.

So, um, overall human history, something more than 100 million people have been killed by sulfate aerosol air pollution.

When sulfur dioxide is released into the atmosphere, it reacts with water vapor to become sulfuric acid.

Which is both naturally put in the stratosphere and also put in the stratosphere by our pollution.

So the way to do sunlight reflection that's most studied and best understood and most technically possible, in the sense that we could start basically now, is putting sulfuric acid droplets of aerosols into the stratosphere.

And why the stratosphere? That's because, uh, materials stay in the stratosphere for about two years, whereas if you put aerosols in the lower atmosphere from, say, a, a pollution source, they just stay for about a week before they fall back to Earth.

What happens when they do eventually fall back to Earth? How, uh, dangerous is it?

So, so, um, it is dangerous, but the good thing about it is we know a lot about what that danger is, and we can quantify it.

And the reason is that, uh, sulfate aerosols are perhaps humanity's worst environmental pollutant of all time, literally.

So, um, overall human history, something more than a hundred million people have been killed by sulfate aerosol air pollution.

Is that fair to say? Can you talk a little bit about some of the controversies in this area?

Sure, but I think...

Maybe I'll start by saying that I've changed my mind and come back to an Aspen event.

So probably the most important to my mind turning point in scientific discussion about sunlight reflection happened here in Aspen in 1998.

There was a smaller meeting than this, not Aspen Ideas.

A gentleman was purporting to say how wonderful sunlight reflection was and to solve all the problems, we didn't need to bother to cut emissions.

I and a friend, Ken Caldera, stood up in the back of the room and said, You're wrong.

Can you tell us what overshoot means for people that may not be familiar?

As I was saying to you before we started recording, uh, on a play on my normal opening question for authors when I ask them what their book is about, I felt we would just sort of start as a level setting thing, explaining terms and whatnot, and ask you, what is geoengineering?

Well, I think it really means two different things that are sometimes lumped together in what I'm now calling climate engineering.

You know, in any disputed topic, people fight about the names.

So, I think there are really two things there.

Um, carbon removal and sunlight reflection.

And you might still say, "What are those things?" And I think the best way to think about what those things are is, is in relation to the whole climate problem.

So, I think fundamentally, the climate problem is a four-dimensional problem.

Mm-hmm.

Give us a 101 if you can.

Maybe the single most important thing to know about climate change is that the amount of warming is proportional to the cumulative emissions over all industrial time.

And that means that even if we brought emissions to zero tomorrow, that wouldn't stop climate change.

It would just stop it getting warmer.

But it would still be warm.

There would still be all the climate damages would be there.

And if we want to reduce the warming, if at any time people want to make the planet cooler than it is when they make that decision, You have to either pull carbon out of the atmosphere or do sunlight reflection, solar geoengineering, or a combination of them.

that i know we've ever done it you've mentioned open ocean aqualinity i just wonder if you could give a quick explanation If you take a glass of