I'm here to talk to you about something
important that may be new to you.

The governments of the world

are about to conduct
an unintentional experiment

on our climate.

In 2020, new rules will require ships
to lower their sulfur emissions

by scrubbing their dirty exhaust

or switching to cleaner fuels.

For human health, this is really good,

but sulfur particles
in the emission of ships

also have an effect on clouds.

This is a satellite image of marine clouds

off the Pacific West Coast
of the United States.

The streaks in the clouds
are created by the exhaust from ships.

Ships' emissions include
both greenhouse gases,

which trap heat over long periods of time,

and particulates like sulfates
that mix with clouds

and temporarily make them brighter.

Brighter clouds reflect
more sunlight back to space,

cooling the climate.

So in fact,

humans are currently running
two unintentional experiments

on our climate.

In the first one, we're increasing
the concentration of greenhouse gases

and gradually warming the earth system.

This works something like a fever
in the human body.

If the fever remains low,
its effects are mild,

but as the fever rises,
damage grows more severe

and eventually devastating.

We're seeing a little of this now.

In our other experiment,

we're planning to remove
a layer of particles

that brighten clouds and shield us
from some of this warming.

The effect is strongest
in ocean clouds like these,

and scientists expect the reduction
of sulfur emissions from ships next year

to produce a measurable increase
in global warming.

Bit of a shocker?

In fact, most emissions contain sulfates
that brighten clouds:

coal, diesel exhaust, forest fires.

Scientists estimate that the total
cooling effect from emission particles,

which they call aerosols
when they're in the climate,

may be as much as all of the warming
we've experienced up until now.

There's a lot of uncertainty
around this effect,

and it's one of the major reasons
why we have difficulty predicting climate,

but this is cooling that we'll lose
as emissions fall.

So to be clear, humans
are currently cooling the planet

by dispersing particles
into the atmosphere at massive scale.

We just don't know how much,
and we're doing it accidentally.

That's worrying,

but it could mean that we have
a fast-acting way to reduce warming,

emergency medicine
for our climate fever if we needed it,

and it's a medicine
with origins in nature.

This is a NASA simulation
of earth's atmosphere,

showing clouds and particles
moving over the planet.

The brightness is the Sun's light
reflecting from particles in clouds,

and this reflective shield
is one of the primary ways

that nature keeps the planet
cool enough for humans

and all of the life that we know.

In 2015, scientists assessed possibilities
for rapidly cooling climate.

They discounted
things like mirrors in space,

ping-pong balls in the ocean,
plastic sheets on the Arctic,

and they found
that the most viable approaches

involved slightly increasing
this atmospheric reflectivity.

In fact, it's possible that reflecting
just one or two percent more sunlight

from the atmosphere

could offset two degrees Celsius
or more of warming.

Now, I'm a technology executive,
not a scientist.

About a decade ago,
concerned about climate,

I started to talk with scientists about
potential countermeasures to warming.

These conversations grew
into collaborations

that became the Marine
Cloud Brightening Project,

which I'll talk about momentarily,

and the nonprofit policy organization
SilverLining, where I am today.

I work with politicians, researchers,

members of the tech industry and others

to talk about some of these ideas.

Early on, I met British
atmospheric scientist John Latham,

who proposed cooling the climate
the way that the ships do,

but with a natural source of particles:

sea-salt mist from seawater

sprayed from ships into areas
of susceptible clouds over the ocean.

The approach became known
by the name I gave it then,

"marine cloud brightening."

Early modeling studies suggested
that by deploying marine cloud brightening

in just 10 to 20 percent
of susceptible ocean clouds,

it might be possible to offset
as much as two degrees Celsius's warming.

It might even be possible
to brighten clouds in local regions

to reduce the impacts caused
by warming ocean surface temperatures.

For example, regions
such as the Gulf Atlantic

might be cooled in the months
before a hurricane season

to reduce the force of storms.

Or, it might be possible to cool waters
flowing onto coral reefs

overwhelmed by heat stress,

like Australia's Great Barrier Reef.

But these ideas are only theoretical,

and brightening marine clouds
is not the only way

to increase the reflection
of the sunlight from the atmosphere.

Another occurs when large volcanoes
release material with enough force

to reach the upper layer
of the atmosphere, the stratosphere.

When Mount Pinatubo erupted in 1991,

it released material
into the stratosphere,

including sulfates that mix
with the atmosphere to reflect sunlight.

This material remained
and circulated around the planet.

It was enough to cool the climate
by over half a degree Celsius

for about two years.

This cooling led to a striking increase
in Arctic ice cover in 1992,

which dropped in subsequent years
as the particles fell back to earth.

But the volcanic phenomenon
led Nobel Prize winner Paul Crutzen

to propose the idea that dispersing
particles into the stratosphere

in a controlled way might be
a way to counter global warming.

Now, this has risks
that we don't understand,

including things like
heating up the stratosphere

or damage to the ozone layer.

Scientists think that there could be
safe approaches to this,

but is this really where we are?

Is this really worth considering?

This is a simulation

from the US National Center
for Atmospheric Research

global climate model showing,
earth surface temperatures through 2100.

The globe on the left visualizes
our current trajectory,

and on the right, a world where particles
are introduced into the stratosphere

gradually in 2020,

and maintained through 2100.

Intervention keeps surface temperatures
near those of today,

while without it, temperatures rise
well over three degrees.

This could be the difference
between a safe and an unsafe world.

So, if there's even a chance
that this could be close to reality,

is this something
we should consider seriously?

Today, there are no capabilities,

and scientific knowledge
is extremely limited.

We don't know whether these types
of interventions are even feasible,

or how to characterize their risks.

Researchers hope to explore
some basic questions

that might help us know
whether or not these might be real options

or whether we should rule them out.

It requires multiple ways
of studying the climate system,

including computer models
to forecast changes,

analytic techniques like machine learning,

and many types of observations.

And though it's controversial,

it's also critical that researchers
develop core technologies

and perform small-scale,
real-world experiments.

There are two research programs
proposing experiments like this.

At Harvard, the SCoPEx experiment
would release very small amounts

of sulfates, calcium carbonate and water
into the stratosphere with a balloon,

to study chemistry and physics effects.

How much material?

Less than the amount released
in one minute of flight

from a commercial aircraft.

So this is definitely not dangerous,

and it may not even be scary.

At the University of Washington,

scientists hope to spray
a fine mist of salt water into clouds

in a series of land and ocean tests.

If those are successful,
this would culminate in experiments

to measurably brighten
an area of clouds over the ocean.

The marine cloud brightening effort
is the first to develop any technology

for generating aerosols for atmospheric
sunlight reflection in this way.

It requires producing
very tiny particles --

think about the mist that comes
out of an asthma inhaler --

at massive scale -- so think
of looking up at a cloud.

It's a tricky engineering problem.

So this one nozzle they developed

generates three trillion
particles per second,

80 nanometers in size,

from very corrosive saltwater.

It was developed by a team
of retired engineers in Silicon Valley --

here they are --

working full-time for six years,
without pay, for their grandchildren.

It will take a few million dollars
and another year or two

to develop the full spray system
they need to do these experiments.

In other parts of the world,
research efforts are emerging,

including small modeling programs
at Beijing Normal University in China,

the Indian Institute of Science,

a proposed center for climate repair
at Cambridge University in the UK

and the DECIMALS Fund,

which sponsors researchers
in global South countries

to study the potential impacts
of these sunlight interventions

in their part of the world.

But all of these programs,
including the experimental ones,

lack significant funding.

And understanding
these interventions is a hard problem.

The earth is a vast, complex system

and we need major investments
in climate models, observations

and basic science

to be able to predict climate
much better than we can today

and manage both our accidental
and any intentional interventions.

And it could be urgent.

Recent scientific reports
predict that in the next few decades,

earth's fever is on a path to devastation:

extreme heat and fires,

major loss of ocean life,

collapse of Arctic ice,

displacement and suffering
for hundreds of millions of people.

The fever could even reach tipping points
where warming takes over

and human efforts are no longer enough

to counter accelerating changes
in natural systems.

To prevent this circumstance,

the UN's International Panel
on Climate Change predicts

that we need to stop
and even reverse emissions by 2050.

How? We have to quickly and radically
transform major economic sectors,

including energy, construction,
agriculture, transportation and others.

And it is imperative that we do this
as fast as we can.

But our fever is now so high

that climate experts say
we also have to remove

massive quantities of CO2
from the atmosphere,

possibly 10 times
all of the world's annual emissions,

in ways that aren't proven yet.

Right now, we have slow-moving solutions
to a fast-moving problem.

Even with the most optimistic assumptions,

our exposure to risk
in the next 10 to 30 years

is unacceptably high, in my opinion.

Could interventions like these
provide fast-acting medicine if we need it

to reduce the earth's fever
while we address its underlying causes?

There are real concerns about this idea.

Some people are very worried
that even researching these interventions

could provide an excuse to delay efforts
to reduce emissions.

This is also known as a moral hazard.

But, like most medicines,

interventions are more dangerous
the more that you do,

so research actually
tends to draw out the fact

that we absolutely,
positively cannot continue

to fill up the atmosphere
with greenhouse gases,

that these kinds of alternatives are risky

and if we were to use them,

we would need to use
as little as possible.

But even so,

could we ever learn enough
about these interventions

to manage the risk?

Who would make decisions
about when and how to intervene?

What if some people are worse off,

or they just think they are?

These are really hard problems.

But what really worries me
is that as climate impacts worsen,

leaders will be called on to respond
by any means available.

I for one don't want them to act
without real information

and much better options.

Scientists think it will take
a decade of research

just to assess these interventions,

before we ever were
to develop or use them.

Yet today, the global level of investment
in these interventions

is effectively zero.

So, we need to move quickly

if we want policymakers
to have real information

on this kind of emergency medicine.

There is hope!

The world has solved
these kinds of problems before.

In the 1970s, we identified
an existential threat

to our protective ozone layer.

In the 1980s, scientists,
politicians and industry

came together in a solution to replace
the chemicals causing the problem.

They achieved this with the only
legally binding environmental agreement

signed by all countries in the world,

the Montreal Protocol.

Still in force today,

it has resulted in a recovery
of the ozone layer

and is the most successful
environmental protection effort

in human history.

We have a far greater threat now,

but we do have the ability
to develop and agree on solutions

to protect people

and restore our climate to health.

This could mean that to remain safe,

we reflect sunlight for a few decades,

while we green our industries
and remove CO2.

It definitely means we must work now

to understand our options
for this kind of emergency medicine.

Thank you,

(Applause)