Transcript Climate Change - Weather Underground

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Chapter 14: Climate
Change
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The earth’s changing climate
Possible causes of climatic change
Global warming
Why Climate Change Matters
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Why should you be aware of climate
change?
Climate is changing and your generation
will be the one to make or break it
Climate change (whether nature or
manmade) will directly affect you!
Determining Past Climates
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How do we know what past climates were
like?
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Fossil evidence
 Fossils of tundra plants in New England
suggest a colder climate
Ocean sediment cores
 Certain animals must have lived in a range of
ocean temperatures
Oxygen isotope ratios
 Differing isotope counts mean differing
temperatures
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Determining Past Climates
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How do we know what past climates were
like?
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Ice cores
 Sulfuric acid in ice cores
 Oxygen isotopes (cold the air, the more
isotopes)
 Bubbles in the ice contain trapped composition
of the past atmospheres
Dendrochronology
 Examining tree rings to see growth patterns
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Climate Through the Ages
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Much of Earth’s history was warmer than today
by as much as 15°C
Ice age
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Most recently 2.5 m.y.a.
Beginning marked by glaciers in North America
Interglacial periods (between glacial advances)
When glaciers were at their max (18,000 – 22,000
years ago) sea level 395 feet lower than today
This is when the sea bridge was exposed
• 20,000 years ago the sea level was so low that the
English Channel didn’t even exist.
Climate Through the Ages
Climate Through the Ages
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Temps began to rise 14,000 years ago
Then temps sank again 12,700 years ago
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This is known as the Younger-Dryas
Climate Through the Ages
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Temps rose again to about 5,000 years
ago (Holocene Maximum). Good for
plants
Climate During the Past 1000
Years
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At 1000, Europe
was relatively
warm.
Vineyards
flourished and
Vikings settled
Iceland and
Greenland
Climate During the Past 1000
Years
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From 10001300
Huge famines
due to large
variations in
weather. Crops
suffered.
Floods and
great droughts
Climate During the Past 1000
Years
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From 14001800
Slight cooling
causes glaciers
to expand
Long winters,
short summers.
Vikings died
Known as the
Little Ice Age
Climate During the Past 1000
Years
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Little Ice Age
1816 – “Year
Without A
summer”
Very cold
summer followed
by extremely cold
winter
Temperature Trend During the
Past 100-plus Years
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Warming from 1900 to 1945
Cooling to 1960, then increasing to today
Temperature Trend During the
Past 100-plus Years
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Sources of temperature readings
Over land, over ocean, sea surface temps
 Warming in 20th century is 0.6°C
 Is global warming natural or manmade?
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External Causes of Climate
Change
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How can we change the climate?
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Changes in incoming solar radiation
Changes in the composition of the
atmosphere
Changes in the earth’s surface
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• Emissions of CO2 and other greenhouse gases are
by no means the only way to change the climate.
Climate Change and
Feedback Mechanisms
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Water vapor-greenhouse feedback
Explain it (is it positive or negative?)
 Runaway greenhouse effect
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Negative feedback mechanisms
Increase in temp…increase in radiant energy
to space
 What planet as a runaway greenhouse effect?
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Snow-albedo feedback (what kind is it?)
Climate Change, Plate
Tectonics, and Mountainbuilding
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Theory of plate tectonics – moving of plates like boats on a
lake
Evidence of plate tectonics
 Glacial features in Africa near sea level
 Fossils of tropical plants in high latitudes
Climate Change, Plate
Tectonics, and Mountainbuilding
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Landmasses at high latitude create glaciers
Arrangements of landmasses disturb ocean
currents
Mountain building by plates running into each
other
Climate Change and
Variations in the Earth’s Orbit
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Milankovitch theory
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As Earth moves around the sun, three
different movements affect solar radiation
Climate Change and
Variations in the Earth’s Orbit
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Eccentricity
 Change in the shape of the orbit (from circular to
elliptical
 Cycle is 100,000 years
 More elliptical,
more variation in
solar radiation
Presently in
Low eccentricity
Climate Change and
Variations in the Earth’s Orbit
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Obliquity
Change in the tilt of Earth’s axis
 Cycle is 41,000 years
 Smaller the tilt, the less seasonal
variation
 Axis tilts from 22° to 24.5°
 What is our current tilt
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Climate Change and
Variations in the Earth’s Orbit
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Procession
Wobble of the Earth as it spins
 The Earth wobbles like a top
 Currently, closest to the sun in
January
 In 11,000 years, closest to the
sun in July
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Climate Change and
Variations in the Earth’s Orbit
Climate Change and
Atmospheric Particles
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Sulfate aerosols
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Put into the atmosphere by sulfur fossil fuels
and volcanoes
• Sulfate aerosols are thought to cool the climate and
therefore counteract global warming to some extent.
Climate Change and
Atmospheric Particles
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Volcano aerosols
May get into the stratosphere and absorb and
reflect sunlight
 Thus, warms the stratosphere and cools the
troposphere
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Climate Change and
Atmospheric Particles
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Volcanic eruptions may be responsible for
many of the climate’s cooling periods
(Little Ice Age)
Eruptions were larger 2.5 m.y.a and may
be responsible for the Ice Age
Climate Change and
Variations in Solar Output
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Sunspots – magnetic storms on the sun
that show up as dark region
Maximum
sunspots,
maximum
emission (11
years)
Maunder minimum
– 1645 to 1715
when few
sunspots
happened
The Recent Warming
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Radiative forcing agents – greenhouse
gases that can disturb the radiative
equilibrium
• Climate models are used to see
the future
• They use data from Carbon
dioxide, other greenhouse gases,
aerosols, and more
Future Warming - Projections,
Questions and Uncertainties
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Questions and uncertainties
 How fast will Carbon dioxide increase?
 Can we stop deforestation?
 Can we stop burning fossil fuels?
Future Warming - Projections,
Questions and Uncertainties
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Uncertain effect of clouds
 More clouds, more reflection to space?
 More clouds, more longwave radiation absorbed?
Possible Consequences of
Global Warming
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Projected temperatures
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Temperatures will rise most in high latitudes
Expanding boreal forest will increase temps
Plants and animals will die
Precipitation will increase worldwide
Possible effects on global circulation
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Weather shifts from normal pattern
More rain than snow in the West
Rise in sea level
Melting glaciers
Contamination of groundwater
Possible Consequences of
Global Warming
Possible Consequences of
Global Warming
Fig. 14-20, p. 407
Global Warming and Human
Impact on the Earth’s Surface
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Desertification – process of overgrazing
and excessive cultivation of grasslands,
causing desert conditions
An interesting theory
Plagues could be nature’s way of “curing” the
Earth of Global Warming
 Plagues kills us and our effects, allowing the
Earth to heal (Gaia Hypothesis)
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Curbing Global Warming
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Kyoto Protocol
A format agreement by hundreds of nations to
curb greenhouse emissions
 Try to reduce emissions by 5% below 1990
levels by 2012
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Geoengineering
Trying to fix the atmosphere with technology
 Idea to put sulfate aerosols into atmosphere
to cool it
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