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

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The governments of the world

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are about to conduct
an unintentional experiment

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on our climate.

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

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by scrubbing their dirty exhaust

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or switching to cleaner fuels.

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For human health, this is really good,

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but sulfur particles
in the emission of ships

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also have an effect on clouds.

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This is a satellite image of marine clouds

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off the Pacific West Coast
of the United States.

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

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Ships' emissions include
both greenhouse gases,

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which trap heat over long periods of time,

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and particulates like sulfates
that mix with clouds

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and temporarily make them brighter.

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Brighter clouds reflect
more sunlight back to space,

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cooling the climate.

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So in fact,

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humans are currently running
two unintentional experiments

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on our climate.

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

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and gradually warming the earth system.

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This works something like a fever
in the human body.

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If the fever remains low,
its effects are mild,

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but as the fever rises,
damage grows more severe

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and eventually devastating.

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We're seeing a little of this now.

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In our other experiment,

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we're planning to remove
a layer of particles

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

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The effect is strongest
in ocean clouds like these,

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

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to produce a measurable increase
in global warming.

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Bit of a shocker?

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In fact, most emissions contain sulfates
that brighten clouds:

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coal, diesel exhaust, forest fires.

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Scientists estimate that the total
cooling effect from emission particles,

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

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

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There's a lot of uncertainty
around this effect,

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

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

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So to be clear, humans
are currently cooling the planet

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by dispersing particles
into the atmosphere at massive scale.

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

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That's worrying,

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

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emergency medicine
for our climate fever if we needed it,

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and it's a medicine
with origins in nature.

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This is a NASA simulation
of earth's atmosphere,

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showing clouds and particles
moving over the planet.

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

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and this reflective shield
is one of the primary ways

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that nature keeps the planet
cool enough for humans

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and all of the life that we know.

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In 2015, scientists assessed possibilities
for rapidly cooling climate.

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They discounted
things like mirrors in space,

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

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and they found
that the most viable approaches

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involved slightly increasing
this atmospheric reflectivity.

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

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from the atmosphere

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could offset two degrees Celsius
or more of warming.

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

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About a decade ago,
concerned about climate,

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

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These conversations grew
into collaborations

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that became the Marine
Cloud Brightening Project,

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which I'll talk about momentarily,

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

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I work with politicians, researchers,

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members of the tech industry and others

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to talk about some of these ideas.

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Early on, I met British
atmospheric scientist John Latham,

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

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but with a natural source of particles:

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sea-salt mist from seawater

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

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

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"marine cloud brightening."

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Early modeling studies suggested
that by deploying marine cloud brightening

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in just 10 to 20 percent
of susceptible ocean clouds,

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

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It might even be possible
to brighten clouds in local regions

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to reduce the impacts caused
by warming ocean surface temperatures.

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For example, regions
such as the Gulf Atlantic

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might be cooled in the months
before a hurricane season

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to reduce the force of storms.

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

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overwhelmed by heat stress,

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like Australia's Great Barrier Reef.

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But these ideas are only theoretical,

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and brightening marine clouds
is not the only way

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to increase the reflection
of the sunlight from the atmosphere.

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Another occurs when large volcanoes
release material with enough force

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

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When Mount Pinatubo erupted in 1991,

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it released material
into the stratosphere,

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including sulfates that mix
with the atmosphere to reflect sunlight.

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This material remained
and circulated around the planet.

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

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for about two years.

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

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

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But the volcanic phenomenon
led Nobel Prize winner Paul Crutzen

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to propose the idea that dispersing
particles into the stratosphere

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

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

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including things like
heating up the stratosphere

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or damage to the ozone layer.

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Scientists think that there could be
safe approaches to this,

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but is this really where we are?

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Is this really worth considering?

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This is a simulation

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from the US National Center
for Atmospheric Research

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global climate model showing,
earth surface temperatures through 2100.

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The globe on the left visualizes
our current trajectory,

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

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gradually in 2020,

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and maintained through 2100.

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Intervention keeps surface temperatures
near those of today,

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while without it, temperatures rise
well over three degrees.

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

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

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is this something
we should consider seriously?

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Today, there are no capabilities,

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and scientific knowledge
is extremely limited.

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

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or how to characterize their risks.

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Researchers hope to explore
some basic questions

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

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or whether we should rule them out.

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It requires multiple ways
of studying the climate system,

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including computer models
to forecast changes,

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analytic techniques like machine learning,

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and many types of observations.

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And though it's controversial,

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it's also critical that researchers
develop core technologies

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and perform small-scale,
real-world experiments.

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There are two research programs
proposing experiments like this.

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At Harvard, the SCoPEx experiment
would release very small amounts

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

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to study chemistry and physics effects.

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How much material?

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Less than the amount released
in one minute of flight

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from a commercial aircraft.

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So this is definitely not dangerous,

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and it may not even be scary.

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At the University of Washington,

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

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in a series of land and ocean tests.

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If those are successful,
this would culminate in experiments

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to measurably brighten
an area of clouds over the ocean.

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

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for generating aerosols for atmospheric
sunlight reflection in this way.

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It requires producing
very tiny particles --

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

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

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It's a tricky engineering problem.

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So this one nozzle they developed

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generates three trillion
particles per second,

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80 nanometers in size,

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from very corrosive saltwater.

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

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here they are --

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

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

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

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

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including small modeling programs
at Beijing Normal University in China,

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the Indian Institute of Science,

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

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and the DECIMALS Fund,

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which sponsors researchers
in global South countries

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to study the potential impacts
of these sunlight interventions

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in their part of the world.

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But all of these programs,
including the experimental ones,

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lack significant funding.

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And understanding
these interventions is a hard problem.

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The earth is a vast, complex system

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and we need major investments
in climate models, observations

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and basic science

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

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and manage both our accidental
and any intentional interventions.

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And it could be urgent.

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Recent scientific reports
predict that in the next few decades,

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earth's fever is on a path to devastation:

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extreme heat and fires,

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major loss of ocean life,

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collapse of Arctic ice,

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displacement and suffering
for hundreds of millions of people.

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The fever could even reach tipping points
where warming takes over

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and human efforts are no longer enough

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to counter accelerating changes
in natural systems.

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To prevent this circumstance,

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the UN's International Panel
on Climate Change predicts

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

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

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including energy, construction,
agriculture, transportation and others.

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

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But our fever is now so high

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that climate experts say
we also have to remove

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massive quantities of CO2
from the atmosphere,

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

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in ways that aren't proven yet.

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

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Even with the most optimistic assumptions,

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our exposure to risk
in the next 10 to 30 years

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is unacceptably high, in my opinion.

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

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

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There are real concerns about this idea.

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Some people are very worried
that even researching these interventions

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could provide an excuse to delay efforts
to reduce emissions.

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This is also known as a moral hazard.

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But, like most medicines,

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interventions are more dangerous
the more that you do,

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so research actually
tends to draw out the fact

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that we absolutely,
positively cannot continue

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to fill up the atmosphere
with greenhouse gases,

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that these kinds of alternatives are risky

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and if we were to use them,

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we would need to use
as little as possible.

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But even so,

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could we ever learn enough
about these interventions

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to manage the risk?

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Who would make decisions
about when and how to intervene?

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What if some people are worse off,

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or they just think they are?

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These are really hard problems.

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

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

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

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and much better options.

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Scientists think it will take
a decade of research

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00:13:01,116 --> 00:13:03,265
just to assess these interventions,

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00:13:03,289 --> 00:13:05,685
before we ever were
to develop or use them.

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Yet today, the global level of investment
in these interventions

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00:13:10,820 --> 00:13:12,871
is effectively zero.

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So, we need to move quickly

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00:13:16,816 --> 00:13:20,038
if we want policymakers
to have real information

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on this kind of emergency medicine.

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There is hope!

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The world has solved
these kinds of problems before.

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In the 1970s, we identified
an existential threat

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to our protective ozone layer.

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In the 1980s, scientists,
politicians and industry

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

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They achieved this with the only
legally binding environmental agreement

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signed by all countries in the world,

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the Montreal Protocol.

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Still in force today,

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it has resulted in a recovery
of the ozone layer

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and is the most successful
environmental protection effort

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in human history.

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We have a far greater threat now,

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

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to protect people

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and restore our climate to health.

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This could mean that to remain safe,

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we reflect sunlight for a few decades,

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while we green our industries
and remove CO2.

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It definitely means we must work now

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to understand our options
for this kind of emergency medicine.

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Thank you,

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(Applause)