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Clouds. They seem so simple.
When they appear darker we pack

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an umbrella. When they're
nowhere in sight, we pack extra

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sunscreen. Either way, we look
to clouds for more information

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than you might realize. But for
all that they can tell us they

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actually remain quite
mysterious, especially when it

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comes to how they impact the
climate. The question is because

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clouds are produced by the
climate, how will it change in

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climate impact clouds? And
conversely, clouds have an

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impact on our climate. So how
will a change in clouds affect a

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change in climate?

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Welcome to Clouds 101. Like all
good mysteries, this one begins

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with a sophisticated scientific
concept, Earth's radiation

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budget. Earth's radiation budget
describes the delicate balance

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between the sun's radiant energy
that reaches Earth, and the

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radiant energy that flows from
Earth back out to space. About

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30% of the sun's incoming
energy, essentially, the light

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and heat we're familiar with is
reflected back to space by

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gaseous molecules in the
atmosphere, tiny particles

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called aerosols, land, snow and
ice surfaces, and by clouds. The

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remaining energy from the sun,
roughly 70%, is absorbed by the

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planet. Most of this absorbed
energy heats up Earth's surface,

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while the rest is absorbed in
the atmosphere by gas molecules,

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clouds, and aerosols. So heat
can be both absorbed and

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reflected by clouds. We'll come
back to this later. Heat is also

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separately emitted by earth into
space in the form of thermal

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infrared radiation, which is the
kind of heat humans can only see

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through night vision goggles.
For Earth's temperature to

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remain constant, the absorbed
solar radiation and outgoing

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thermal infrared radiation must
balance one another. If the

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Earth's system is changed,
either through natural phenomena

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like volcanic activity, or
through unnatural phenomena like

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humans burning fossil fuels, an
imbalance in Earth's radiation

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budget occurs, and as a result,
the earth's temperature

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eventually increases or
decreases to restore an energy

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balance. In recent decades,
satellite and surface

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measurements clearly show an
energy imbalance taking place

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that's been increasing. Over the
past 150 years. The large rise

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in carbon dioxide emissions,
which accumulate in the

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atmosphere, has created an
enhanced greenhouse effect. This

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means that energy from the sun
still easily reaches Earth, but

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Earth's thermal infrared
radiation has a harder time

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getting out into space. This has
caused a decrease in how much

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heat Earth sheds. Consequently,
we have observed a rise in

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Earth's global mean surface
temperature, an increased

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melting of snow and sea ice, sea
level rise, and more extreme

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weather events. So that brings
us back to the mystery of

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clouds' long term effects on
climate. Here's what we know so

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far. Clouds impact the radiation
budget in two ways: by

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reflecting solar radiation back
to space, which leads to a

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cooling effect on the climate,
and by absorbing heat emitted

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from below the clouds that would
have otherwise escaped to space

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if the clouds weren't present,
leading to a warming effect.

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Which of these effects dominates
in any given location depends

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upon the cloud type. High
altitude clouds are typically

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thinner and colder than low
clouds, allowing for more solar

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radiation to pass through them
and reach Earth's surface. And

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because they're cooler, they
emit less thermal infrared

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radiation to space, so they have
a net warming effect on the

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climate. Clouds at low
altitudes, on the other hand,

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are generally thicker and
reflect more solar radiation

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back out to space. They're also
typically warmer, so they emit

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more thermal infrared radiation
and therefore have a net cooling

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effect on the climate. We also
know that when the climate

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warms, Earth can respond in ways
that leads to further warming.

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For example, as temperatures
increase, we see snowpack and

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sea ice melting away in polar
regions, a loss of white

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surfaces that reflect the solar
radiation. That means darker

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colored land and oceans left
behind absorb more solar

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radiation, and so more heat is
added to the climate system.

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This cycle of more heat, more
melt and more absorption of

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solar radiation is called a
feedback cycle. And it doesn't

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end there. A feedback cycle also
happens with clouds. Climate

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models predict a decrease in low
altitude cloud coverage over the

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globe as the climate warms,
since low clouds are the highly

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reflective type, a decrease in
low cloud coverage means more

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heat will be added to the
Earth's system, leading to

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further warming. And clouds
impact the climate in another

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way too: Through the water cycle
producing rain and snowfall.

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Water at Earth's surface
evaporates, providing the

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atmosphere with a supply of
water vapor. Depending on the

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air temperature and atmospheric
pressure, the air can only hold

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so much water vapor until it
becomes saturated. When that air

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saturated with water vapor
cools, the water vapor turns

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back into liquid water droplets
and forms clouds.

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When these droplets or ice
crystals accumulate, that is

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what we call a cloud. When the
droplets or ice crystals within

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the cloud grow to be large
enough, they eventually fall to

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the ground or ocean as rain,
snow or hail. This brings us

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back to the mystery at hand.
Because clouds both reflect and

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absorb energy from the sun
impacting both ends of the

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radiation balance and play a
massive role in the water cycle,

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any changes in clouds will
result in a change in our

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climate. But clouds are also
produced by our climate, so any

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change in climate will result in
a change in clouds. As you

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probably now realize the
relationship between clouds and

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the climate is incredibly
complex, and NASA is on a

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mission to understand it. Using
NASA's Earth Observing fleet of

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satellites like Calipso and
instruments like Ceres and

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MODIS, scientists have been
collecting vital data on clouds

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to be able to precisely model
their behavior. A key ingredient

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to unraveling the mystery of
clouds lies in the collection of

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global accurate multi decadal
climate data records of cloud

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properties and their influence
on Earth's radiation budget.

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Once we can accurately and fully
understand the physics of clouds

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through observations, that data
can then be used to help improve

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climate and weather models so we
can better prepare for the future.