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 LONGERTIME SCALE

CLIMATE PREDICTION IS NOT EQUAL TO WEATHERPREDICTION

CLIMATE INCLUDES NEW PROCESSES NOT PART OFWEATHER

E.G. CONTINENTAL DRIFT, EARTH ORBITALVARIATIONS, ...

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

(red line is myrough average)

Note SHARP changesin climate found in data (Greenland cores)

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.