Transcript Lecture I

CLIMATE:
DEFINITION: THE AVERAGE VALUE OF "WEATHER"
PARAMETERS AT A SPECIFIED SCALE
OVER A SPECIFIED TIME SCALE
(LONGER THAN A FEW DAYS)
SCALES:
MICRO- MESO- MACRO- (OR GLOBAL)
PHYSICAL PROCESSES OF CLIMATE:
SAME AS "WEATHER" PROCESSES, BUT LONGER
TIME SCALE
CLIMATE PREDICTION IS NOT EQUAL TO WEATHER
PREDICTION
CLIMATE INCLUDES NEW PROCESSES NOT PART OF
WEATHER
E.G.
CONTINENTAL DRIFT, EARTH ORBITAL
VARIATIONS, ...
COMPONENT:
SOME POSSIBLE CHANGES
LITHOSPHERE:
RADIATION LOSSES AND/OR
CHANGES IN ABSORPTION...
CONTINENTAL DRIFTS
ATMOSPHERE:
COMPOSITIONAL CHANGES,
PARTICULATES,...
HYDROSPHERE:
COMPOSITIONAL CHANGES,
EFFECTS OF WINDS, ...
CRYOSPHERE:
VARIABILITY OF EXTENT,
ALBEDO EFFECTS,
DAISY WORLD,
LIGHT/DARK
DASIES
EFFECT OF
DASIES ON
GLOBAL CLIMATE
EFFECT OF CARBON DIOXIDE ON GLOBAL
CLIMATE AS SUN EVOLVES AND WARMS.
The Ice Ages
What is an Ice Age
• Ice ages are times when large areas of the
earths surface are covered with ice sheets
• The term can be used to describe time
periods when the earth is at a cooler
temperature than usual(10-100 million
years), or shorter time periods when glaciers
are at their maximum extent (10s of
thousands of years)
Causes of Ice Ages
• There are many factor thought to influence
the creation of ice ages
• Plate Tectonics
• Milankovich Cycles
• Ocean and Atmospheric Circulation
• Volcanic eruptions
• Solar Cycles (i.e. Sunspots)
Plate Tectonics
• Plate tectonics is believed to be a factor in
the development of ice ages
• Large ice sheets can form when landmasses
are in and near polar regions
• Plate tectonics also can affect atmospheric
and ocean currents
EXTERNAL INFLUENCES ON CLIMATE
VARIATIONS IN EARTH'S ORBIT AND OTHER
EXTERNAL INFLUENCES SUCH AS SOLAR OUTPUT
CHANGES, COLLISIONAL IMPACTS...
ARE THERE PREDICTABLE LONG TERM CLIMATE
CHANGES ?????
LOUIS AGASSIZ' ICE AGES...
MILANKOVIC THEORY....
...AND EARTH ORBITAL VARIATIONS
Milankovich Cycles
• Milankovich Cycles arise from orbital
variation of earth about the sun
• There are three main variations in the
earth’s motion around the sun; Orbital
Eccentricity, Obliquity, and Precession
• These factors affect the amount of radiation
the earth receives from the sun
Orbital Eccentricity
• The earths orbit around the sun is slightly
elliptical with the elongation of the ellipse
changing about every 100,000 years
• The more elliptical the orbit of the earth, the
greater the contrast in temperature between
summers and winters in both hemispheres
Orbital Eccentricity
Obliquity
• The axis of the earth is tilted 23.5 degrees at
this time
• The tilt of the earth varies from 22.1
degrees to 24.5 degrees
• The tilt of the earth varies on a 41,000 year
cycle
• The smaller the tilt angle, the less radiation
the poles receive
Obliquity
Precession
• Precession is just the wobble of the earth
axis
• The means that the seasons are not always
at the same spot on the earths orbit
• A Precession cycle takes about 23,000 years
Precession
Milankovich Cycles
• The conditions most conducive to an ice age
would be
• Orbital eccentricity at its maximum
• Obliquity at its minimum
• Precession so that summer is farthest from
the sun and winter is closest to the sun
Solid red line is “my average”,
Data show large, fast changes
CLIMATE CHANGE ON A DECADAL SCALE
INFLUENCING MECHANISMS:
SOLAR CYCLE, ANNULAR, DIURNAL VARIABILITY
VOLCANIC ACTIVITY
ATMOSPHERIC-OCEAN INTERACTION
CRYOSPHERE (VARIABILITY)
HUMAN ACTIVITIES
Atmospheric and Oceanic
Circulation
• Changes in Atmospheric and Oceanic
Circulation can promote the beginning of an
ice age
• E.G. currents that bring warmer water near
the polar regions can start ice ages because
of increased precipitation, as resulted from
opening Strait of Magellan 25 M years ago
Atmospheric and Oceanic
Circulation
• For example, 3.5 million years ago, the
Isthmus of Panama formed,and cut off eastwest ocean current circulation. This
strengthened the gulf stream. The gulf
stream then brought warmer water to the
northern hemisphere which increased
precipitation over the north pole, initiating
the formation of ice sheets, as the theory
goes...
Volcanic eruptions
• Volcanic eruptions can reduce the radiation
from the sun that reaches the surface of the
earth by the release of ash into the air
• Only extremely large, or continuing
eruptions can effect global climate
• The Mt Pinatubo eruption in 1991 cooled
the climate of Europe by about 1 degree for
1 year.
• A more dramatic example, is shown Mt.
Tambora eruption of April 10, 1815...
Volcanic Eruptions
Sunspots
• Sunspots are magnetic storms on the sun. These
regions are cooler than the rest of the sun
• The solar wind is increased when there are more
sunspots, because of high magnetic activity which
enhances particle ejection processes
• Thus fewer sunspots means less energetic input
from the sun which lowers Earth’s temperature, as
occurred in the ‘Maunder Minimum(~1650 -1720)
Factors lengthening ice ages
• Once large continental ice sheets form they
create a positive feedback loop making the
temperature colder
• This results from the high albedo for ice,
which reflects solar insolation well
• Thus less of the Sun’s radiation is absorbed
by the Earth, reducing the temperature
Additional factors
• Glaciation causes heavy erosion of rocks by
ice grinding the rock surface
• This releases minerals and rock debris to
exposure to the air and reaction with CO2
• This causes a reduction of CO2 which
causes an “Ice house” effect
Some Effects of Ice ages
• Rise and fall of sea level as water is
contained/released from glaciers on land into the
oceans (not sea ice)
• Great amounts of erosion and deposition
• For example: carving of mountain valleys by
glaciers, and formation of the flat topography and
rich soils in the northern Midwest
• Isostatic depression and rebound from effects of
continental glaciers
ISOSTATIC DEPRESSION OF A CONTINENT
ISOSTATIC REBOUND IS CONTINUING IN
SCANDANAVIA TODAY...
Predictions for the next ice age
• Predictions are that the next glaciation will occur
sometime after the next 5,000 years ??
• This is based on the Milankovich Cycle Theory
• The greenhouse effect could make it more difficult
for ice ages to happen, or could accelerate it...
• A catastrophic volcanic eruption could occur at
any time, releasing atmospheric aerosols …
• e.g. Yellowstone and Huckleberry Ridge...
THE RECORD SHOWS THAT:
1.
A NEW GLACIATION IS EXPECTED (BASED ON PAST)
2.
IT MAY BE DELAYED BY GLOBAL WARMING DUE TO
CO2 AND OTHER GREENHOUSE GASES
3.
ABRUPT CLIMATE CHANGE OCCURS (E.G. AS
SHOWN BY GREENLAND/ANTARCTIC ICE CORES)
4.
THE CHANGES MAY BE LONG LASTING COMPARED
WITH HUMAN TIME SCALES
THE UNKNOWNS
1.
IS THE PRESENT CLIMATE STABILITY ILLUSORY?
2.
CAN WE ACCIDENTLY SHIFT THE CLIMATE STATE?
3.
HOW STABLE (HOW LONG LASTING) WILL A
CLIMATE SHIFT BE?
4.
GIVEN THE UNCERTAINTIES, WHAT IS A
POPULATION FOR THE EARTH CONSISTENT WITH
THE CLOSED SYSTEM AND CLIMATE
VARIATIONS????