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, ...
What is an Ice Age ?
• Ice ages are times when large areas of the
earths surface are covered with ice sheets
• The term is used to describe time periods
when
• a) the earth is at a cooler temperature than
usual(10-100 million years), or
• b)shorter time periods when glaciers are at
their maximum extent(10s of thousands of
years) = Glaciation Cycle
Causes of Ice Ages
• There are many factors thought to
influence the start and end of ice ages
• Milankovich Cycles
• Plate Tectonics
• Ocean and Atmospheric Circulation
• Volcanic eruptions
• Sunspots
Milankovich Cycles
• Milankovich Cycles deal with the way the
earth travels around the sun
• There are three main ways in which the
earth changes its 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
Tilt: smaller
larger
Precession
• Precession is 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
Change of time of year when Earth is nearest to the Sun (now January)
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
Note SHARP changes
in climate found in
data (Greenland cores)
(red line is my
rough average)
Toba eruption
Plate Tectonics
• Plate tectonics is an important factor in the
development of ice ages
• There needs to be landmasses in and
near the polar regions for large ice sheets
to start to form
• Plate Tectonics also can affect
atmospheric and ocean currents
Atmospheric and Oceanic
Circulation
• Changes in Atmospheric and Oceanic
Circulation can promote the beginning of
an ice age
• Any change in these currents that brings
warmer water near the polar regions can
start ice ages because of increased
precipitation
Atmospheric and Oceanic
Circulation
• For example, 3.5 million years ago, the
Isthmus of Panama formed. The cut off
east-west ocean current circulation, which
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.
• That is, warmer conditions apparently
yielded a glaciation cycle!
Volcanic eruptions
• Violent volcanic eruptions can effect the
radiation from the sun that reaches the
surface of the earth by releasing great
quantities of ash into the air
• It takes an extremely large eruption to
effect global climate, e.g. Mt. Tambora,
1815, Toba, 70,000 BC
• The Mt Pinatubo eruption in 1991 only
affected the climate of Europe by about 1
degree for 1 year
Volcanic Eruptions
Sunspots
• Sunspots are solar magnetic regions that are
cooler than the rest of the sun
• The radiation coming from the sun is raised
when there are more sunspots, even though
they are cold spots
• This is because of great magnetic activity
causes increased radiation
• Thus, fewer sunspots means less radiation
coming from the sun and a lower temperature
for the Earth and its climate
Factors Lengthening Ice Ages
• Once large continental ice sheets form,
they create a positive feedback loop
making the temperature colder
• This is due to the high albedo of ice, which
means that it reflects light well
• Thus, less of the sun’s radiation is
absorbed by the earth and the
temperature drops.
More factors
• Further; glaciation causes erosion of rocks
by the overlying ice
• This takes minerals and rock debris to the
sea where they react with CO2 in the air
• This causes a reduction of CO2 which
results in an “Ice House” Effect
Physical Effects of Ice ages
• Rise and fall of sea level as water is
confined by/released from glaciers
• Great amounts of erosion and sediment
deposition
• E.G.: The carving of mountain valleys by
glaciers, and formation of flat topography
and the rich soils in the northern Midwest
resulted from the glaciation cycles.
• Isostatic depression and rebound from
effects of continental glaciers
Predictions for the next ice age
• Most predicts are that the next ice will occur
sometime between the next 5,000 and 50,000
years
• This is mostly based on Milankovich cycles
• The greenhouse effect could make it more
difficult for ice ages to happen, or can cause one
• On the other hand, catastrophic volcanic
eruption of epic proportions can occur at any
time (Huckleberry Ridge model of Yellowstone)
• There would drastic effects on human
populations, if any of these occur while
populations are high.