Slide 1
Climate Sensitivity and
Feedback
Climate Changes
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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 |
Tectonic Scale
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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. |
Orbital Scale
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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. |
Major Climate Feedback
Processes
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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 |
Water Vapor Feedback
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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 |
Snow/Ice Albedo 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. |
Longwave Radiation
Feedback
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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 |
Vegetation-Climate
Feedbacks
Cloud 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. |
El Nino-Southern
Oscillation (ENSO)
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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. |
1982-83 El Nino
1997-98 El Nino
El Nino Comparisons
Slide 16
Slide 17
Slide 18
Slide 19
Slide 20
Slide 21
Slide 22
Decadal Changes of ENSO
Slide 24
ENSO and PDO
Pacific Decadal
Oscillation
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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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Decadal Variations (PDO
Index)
Slide 28
North Atlantic
Oscillation
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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. |
Positive and Negative
Phases of NAO
Dynamics Behind NAO
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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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North Atlantic
Oscillation
= Arctic Oscillation
= Annular Mode
Decadal Timescale of
Arctic Oscillation
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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. |