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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 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.