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 of 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 the 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 conversation grew
into collaborations that became

the Marine Cloud Brightening Project,
which I'll talk about momentarily,

and the non-profit policy organization
Silver Lining, where I am today.