Should we create a solar shade to cool the earth?

[A provocation from Danny Hillis:]

[It's time to start talking
about engineering our climate]

What if there was a way
to build a thermostat

that allowed you to turn down
the temperature of the earth

anytime you wanted?

Now, you would think if somebody
had a plausible idea about how to do that

everybody would be very excited about it

and there would be lots
of research on how to do it.

But in fact, a lot of people
do understand how to do that.

But there's not much support
for research in this area.

And I think part of it

is because there's some real
misunderstandings about it.

So, I'm not going to try to convince you
today that this is a good idea.

But I am going to try to get
your curiosity going about it.

And clear up some
of the misunderstandings.

So, the basic idea of solar geoengineering

is that we can cool things down

just by reflecting a little bit
more sunlight back into space.

And ideas about how to do this
have been around literally for decades.

Clouds are a great way to do that,
these low-lying clouds.

Everybody knows it's cooler under a cloud.

I like this cloud because it has exactly
the same water content

as the transparent air around it.

And it just shows

that even a little bit of a change
in the flow of the air

can cause a cloud to form.

We make artificial clouds all the time.

These are contrails,
which are artificial water clouds

that are made by the passing
of a jet engine.

And so, we're already
changing the clouds on earth.

By accident.

Or, if you like to believe it,
by supersecret government conspiracy.

(Laughter)

But we are already doing this quite a lot.

This is a NASA picture of shipping lines.

So passing ships
actually cause clouds to from.

And this is a big enough effect

that it actually helps reduce
global warming already by about a degree.

So, we already are doing
solar engineering.

There's lots of ideas
about how to do this.

People have looked at everything
from building giant parasols,

on to space, to fizzing
bubble waters in the ocean.

And some of these are actually
very plausible ideas.

One that was published recently
by David Keith at Harvard

is to take chalk and put dust
up in the stratosphere

where it reflects off sunlight.

And that's a really neat idea,

because chalk is one of the most
common minerals on earth

and it's very safe, it's so safe
we put it in the baby food.

And basically, if you throw chalk
up into the stratosphere

it comes down in a couple of years
all by itself, dissolved in rainwater.

Now, before you start worrying
about all this chalk in your rainwater,

let me explain to you
how little of it it actually takes.

And that turns out to be
very easy to calculate.

This is a back-of-the-envelope
calculation I made.

(Laughter)

(Applause)

I assure you, people have done
much more careful calculations

and it comes out with the same answer.

Which is that you have to put chalk up
at the rate of about 10 teragrams a year

to undo the effects of the CO2
that we've already done.

Just in terms of temperature,
not all the effects, but the temperature.

So, you know, what does that look like?

I can't visualize 10 teragrams per year.

So I asked the Cambridge
bio department and Taylor Milsal

to lend me a hand.

And this is a hose pumping water
at 10 teragrams a year.

And that is how much

you would have to pump
into the stratosphere

to cool the earth back down
to pre-industrial levels.

And it's amazingly little,
it's like one hose for the entire earth.

Now, of course you wouldn't
really use a hose,

you'd fly it up in airplanes
or something like that.

But, it's so little, it would be like
putting a handful of chalk

into every Olympic
swimming pool full of rain.

It's almost nothing.

So, why don't people like this idea?

Why isn't it taken more seriously?

And there are some
very good reasons for that.

A lot of people really don't think
we should be talking about this at all.

And in fact, I have some
very good friends in the audience,

who I respect a lot,

who really don't think
I should be talking about this.

And the reason is that they're concerned

that if people imagine
that there's some easy way out

that we won't give up
our addiction to fossil fuels.

And I do worry about that.

And it's actually a serious problem.

But there's also, I think,
a deeper problem.

Which is, nobody likes the idea
of messing with the entire earth,

I certainly don't.

I love this planet, I really do.

And I don't want to mess with it.

But we're already changing our atmosphere,

we're already messing with it.

And so I think

it makes sense for us to look for ways
to mitigate that impact.

And that we need
to do research to do that.

We need to understand
the science behind that.

I've noticed that there's a theme
that's kind of developed at TED,

which is kind of, fear versus hope,

or creativity versus caution.

And of course, we need both of those.

So, there aren't any silver bullets,

you know, this is certainly
not a silver bullet.

But we need science to tell us
what our options are

and that informs both
our creativity and our caution.

So, I am an optimist
about our future selves

but I'm not an optimist
because I think our problems are small.

I'm an optimist because I think
our capacity to deal with our problems

is much greater than we imagine.

Thank you very much.

(Applause)

Chris Anderson: Danny, you know we do have
a real-life expert on clouds with us.

Do you mind if I invite her up onstage?

Kate, do you mind
if I invite you back onstage?

We can have a conversation about this.

(Applause)

So, Kate, what did you make
of Danny's talk?

Kate Marvel: Denny, you seem so nice
and I hope we can be friends

and you terrify me.

(Laughter)

I am very worried
about geoingeneering solutions

for many different reasons.

I feel like if I went to the doctor
and the doctor said, "You have a fever.

I know exactly why you have a fever.

We're not going to treat that,
we're just going to give you ibuprofen,

and also your nose is going to fall off."

I would be really upset
and I would want a new doctor.

And I feel like dealing
with climate change

by reducing the amount of sunlight we get

is really problematic.

Because there are physical reasons
to be frightened by that.

For example, it's not going to do
anything about ocean acidification.

And I care very much
about the health of the oceans.

But I think -- I'm a physicist,
but I'm also a human being and a citizen.

And I'm frightened as a citizen.

Because, I feel like, when I want
to do an experiment,

I have to go to my university

and if there are human subjects,
I have to obtain informed consent

from every single human subject.

And I feel like what
you are proposing to do

is involving all of us
as your human subjects

and I'm not sure I consent to that.

(Applause)

Danny Hillis: I sympathize
with all of that.

And I think it would be great
if we lived in a world

where people had to get their consent
before messing with it,

but you are already
in the middle of an experiment.

KM: And I'm not happy
about that one, either.

DH: Right, I'm not, either.

People are already messing
with the atmosphere.

And we don't really understand
the effects of it.

So, we are geoingeneering.

And so what I'm arguing for
is we should understand it,

we should do the research
to understand it.

I'm not claiming it's secure,
but it may be...

It may be something that we need

to help us cool down
while we fix the problem.

And I don't think we can
throw away any options now.

I think we really need
to get the knowledge.

If we're going to do geoingeneering --
which we are going to do,

even if it's a bad idea --

we need to understand it
and we need to do a better job of it.

CA: OK, this is the start of
an incredibly important conversation.

Thank you, both of you,
we're going to continue this.

KM: I hope we can still be friends.

CA: Thank you, thanks Denny.

(Applause)