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Tectonic-Scale Climate Changes |
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Orbital-Scale Climate Changes |
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Deglacial and Millennial Climate Changes |
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Historical Climate Change |
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Anthropogenic Climate Changes |
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Tectonic Scale: the longest time scale of
climate change on Earth, which encompasses most of Earth’s 4.55-billion
years of history. |
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Tectonic processes driven by Earth’s internal
heat alter Earth’s geography and affect climate over intervals of millions
of years. |
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On this time scale, Earth’s climate has
oscillated between times when ice sheets were presented somewhere on Earth
(such as today) and times when no ice sheets were presented. |
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Orbital-scale climate changes are caused by
subtle shifts in Earth’s orbit. |
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Three features of Earth’s orbit around the Sun
have changed over time: |
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(1)
the tilt of Earth’s axis, |
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(2)
the shape of its yearly path of revolution around the Sun |
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(3)
the changing positions of the seasons along the path. |
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Orbital-scale climate changes have typical
cycles from 20,000 to 400,000 years. |
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Water Vapor Feedback - Positive |
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Snow/Ice Albedo Feedback - Positive |
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Longwave Radiation Feedback - Negative |
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Vegetation-Climate Feedback - Positive |
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Cloud Feedback - Uncertain |
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Mixing Ratio = the dimensionless ratio of the
mass of water vapor to the mass of dry air. |
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Saturated Mixing Ratio tells you the maximum
amount of water vapor an air parcel can carry. |
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The saturated mixing ratio is a function of air
temperature: the warmer the temperature the larger the saturated mixing
ration. |
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č a warmer
atmosphere can carry more water vapor |
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č stronger
greenhouse effect |
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č amplify
the initial warming |
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č one of
the most powerful positive feedback |
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The snow/ice albedo feedback is associated with
the higher albedo of ice and snow than all other surface covering. |
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This positive feedback has often been offered as
one possible explanation for how the very different conditions of the ice
ages could have been maintained. |
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The outgoing longwave radiation emitted by the
Earth depends on surface temperature, due to the Stefan-Boltzmann Law: F = s(Ts)4. |
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č warmer
the global temperature |
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č larger
outgoing longwave radiation been emitted by the Earth |
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č reduces
net energy heating to the Earth system |
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č cools
down the global temperature |
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č a
negative feedback |
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Clouds affect both solar radiation and
terrestrial (longwave) radiation. |
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Typically, clouds increase albedo č a
cooling effect (negative feedback) |
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clouds reduce outgoing longwave radiation č a
heating effect (positive feedback) |
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The net effect of clouds on climate depends
cloud types and their optical properties, the insolation, and the
characteristics of the underlying surface. |
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In general, high clouds tend to produce a
heating (positive) feedback. Low clouds tend to produce a cooling
(negative) feedback. |
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ENSO is a interannual (year-to-year) climate
variability in the eastern tropical Pacific Ocean. |
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ENSO is found to have profound impacts on global
climate. |
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“Pacific Decadal Oscillation" (PDO) is a
decadal-scale climate variability that describe an oscillation in northern
Pacific sea surface temperatures (SSTs). |
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PDO is found to affect Alaska salmon production cycles. |
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PDO is found to link to the decadal variations
of ENSO intensity. |
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The NAO is the dominant mode of winter climate
variability in the North Atlantic region ranging from central North America
to Europe and much into Northern Asia. |
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The NAO is a large scale seesaw in atmospheric
mass between the subtropical high and the polar low. |
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The corresponding index varies from year to
year, but also exhibits a tendency to remain in one phase for intervals
lasting several years. |
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The North Atlantic Oscillation is considered as
a natural variability of the atmosphere. |
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However, processes in the ocean and stratosphere
and even the anthropogenic activity can affect its amplitude and phase. |
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Surface winds of the NAO can force sea surface
temperature variability in the Atlantic Ocean. |
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Feedbacks from the ocean further affect NAO
variability. |
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The Arctic Oscillation switches phase
irregularly, roughly on a time scale of decades. |
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There has been an unusually warm phase in the
last 20 years or so, exceeding anything observed in the last century. |
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