Transcript Natural Climate Change

Causes of Climate Change
By: Rajdeep Kaur
What is Climate Change?
 Changes in the Earth's climate, especially those
produced by global warming
 Climate includes patterns of temperature, precipitation,
humidity, wind and seasons.
Main Causes of Climate Change
 The Milankovitch Theory
 Atmospheric Carbon Dioxide Variations
 Volcanic Eruptions
 Variations in Solar Output
 Ocean Currents
 Human activity
Four Categories
 Factors external to the Earth-atmosphere system.
 Factors with a strong geological expression.
 Factors internal to the earth-ocean atmosphere system
 Factors that have a significant randomness
External Factors
 Changes in the sun’s orbit within our galaxy
 Comets
 Changes in solar output
 Changes in orbital parameters (Milankovitch Hypothesis)
Changes in the sun’s orbit within our
galaxy
 A fundamental cycle of 200-300 million years appear to
underlie large scale geological processes, such as
mountain building and plate movements.
 There is a regular crossing by the sun and around the
time of each crossing the solar system encounters more
interstellar dust.
 This periodicity correlates with increased volcanism,
meteor and comet impacts, mass extinctions and
reversals in the Earth’s magnetic field.
 The tilting of the axis of the solar system is not stable,
but undergoes a 100,000 year period with increases in
cosmic dust correlating to interglacial.
Comets
 Comet impacts with the Earth, or crossing the earth’s
orbit, can also increase extraterrestrial dust fallout.
 Even objects smaller than one kilometer in diameter can
have a major impact on climate, recent evidence
suggests that the actual incidence of small objects
hitting the Earth is ore common than previously
recognized.
 Comets do not have to crash into the Earth to affect the
earths climate.
 The Earth’s orbit often intersects the tall of debris
formed in the path of such a fragmenting comet orbiting
the sun.
Changes in solar output
 The sun does not emit radiation constantly over time.
 An important product of solar activity in the
atmospheres the formation of radioactive carbon 14.
 When solar activity is high and by inference sunspots
numerous, cosmic rays are deflected form the earth’s
stratosphere by the solar wind then the production of
carbon 14 is less and it correlates to warmer
temperatures.
 Increasing radiation first led to glaciation because of
increased evaporation, more cloud, greater planetary
albedo and increased snowfall, especially in mountainous
regions.
Milankovitch Theory
 There are three cycles to the Milankovitch cycle.
 The theory of climatic effect is usually attributed to the
Yugoslav geophysicist Milutin Milankovitch, who
transformed the earlier semi-quantitative work by James
Croll into the mathematical framework of an
astronomical theory of climate.
Eccentricity
Axial Tilt
Precession of the equinox
Geological Factors
 Continental Drift
 Mountain Building
 Volcanism
 Geomagnetism
Continental drift
 Continental drift created the atmospheric and oceanic
conditions favorable for global glaciation.
 The Antarctic circumpolar current occurred about fifty
million years age and it prevented the exchange of
warmer water form the tropics with Antarctic water,
dropping temperatures by several degrees.
 Northwards movement of continents restricted the
exchange of ocean water with the Arctic ocean, virtually
creating a shallow inland sea that has been ice-covered
since the Pliocene.
 Global glaciation reduced sea-levels, exposing more of
the shallow sea’s seabed to sub-aerial glaciation.
Mountain Building
 Most modern glaciers are found in mountainous regions
because of locally moister and globally cooler conditions
at high elevations.
 majority of the Earth's glaciers are found in the
American Cordillera (Andean, and Rockies), Alps, and
Himalaya.
 Mountains can cause glaciation by providing cooler
locations for icecaps to develop, by altering patterns of
atmospheric circulation, especially in the upper
atmosphere, and by changing the geochemical
composition of the oceans.
 However, mountains cannot explain alternate glacial and
interglacial changes in climate.
Volcanism
 It was Benjamin Franklin who first identified the
potential of volcanoes to alter the climate. (he suggested
that the winter of 1783-84 in northern Europe was
caused by the dust cloud produced by the huge eruption
of laki in Iceland in July 1783, which dimmed the sun in
Paris for months on end.
Volcanism

It was discovered that major volcanoes do cool the climate to ground
level and there is a compensating and somewhat greater warming of the
stratosphere.

A dust veil in the upper atmosphere absorbs sunlight, this heats the
stratosphere but causes compensating cooling at lower levels, as less
solar radiation reaches the earth’s surface. Analysis of past eruptions
have suggests that this had a significant impact on the climate.

The effects of a single eruption lasts about 2-3 years.

Major eruptions produce a substantial drop in the summer temperatures
for two or three years and the effect on winter temperatures is a
warming, owing to stronger westerly circulation to mid-to-high latitudes.

Volcanic eruptions could be triggered by sudden sustained changes in
atmospheric circulation.

Volcanoes can alter climate in three ways:

Increased carbon dioxide

Increased sulphate aerosols

Enhanced dust ejection into the stratosphere
Volcanoes
 Some major volcanoes:
 Mount St. Helens
 El Chichon in Mexico
 Mount Pinatubo
Geomagnetism
 The earth's magnetic field is modulated by the core-mantle
boundary.
 The field reverses about three times in any million year period and
reversals take 5,000 years to complete and affect climate.
 There have been findings on stronger geomagnetic field during
glacial cycles, and for warmer temperatures at locations on the
earth where magnetic intensity has been decreasing.
 As solar wind increases, so does the earths’ temperatures and it can
be generated by solar flares independent of the sunspot cycle.
 The strongest and most frequent development of cellular blocking
occurs when the solar wind, and its corresponding geomagnetic
activity on the earth, are strongest.
 Also there is strong wiring in the stratosphere leading to enhanced
zone production and absorption of solar radiation.
Land-Ocean-atmosphere System
 Carbon dioxide and methane changes
 Ocean heating and cooling
 Albedo changes in ice, snow and dust
Changes in atmospheric composition
 The higher levels of carbon dioxide in the atmosphere
during, the cretaceous period had an important factor in
the maintenance of the benign climate of that period.
 There are subtle differences between the changes in the
temperatures and the rise and fall in the levels of carbon
dioxide and methane . This suggests that other climatic
factors were the primary cause of the shift in the
climate, and the changes in greenhouse gases may have
been no more than a secondary factor.
Carbon dioxide and methane
changes
 Both carbon dioxide and methane are greenhouse gases
that have a significant forcing effect upon long wave
radiation emitted by the earths’ surface.
 Both differ in their behavior overtime, and show intrinsic
differences between glacial and interglacial that cannot
be linked to temperatures.
 Without significant upwelling of deep bottom water, the
carbon dioxide is not returned efficiently to the ocean
surface during glacial and thus is removed closely form
the atmosphere.
Ocean heating and cooling
 There are strong correlations between oceans and air
temperatures on global, hemispheric and regional scales.
 A cooler globe did not necessarily lead to a cooler ocean
especially in the tropics and therefore land ocean
temperature relationships may have behaved very
differently between glacial and interglacial.
 In terms of causes of climate change, there is a major
point whether these changes can be regarded as
principally matters of ocean circulation.
Albedo changes in ice, snow an dust
 Greater positive feedback effects upon planetary albedo,
and resulting global cooling, were induced by changes in
the amount of sea-ice, glacial ice and snow.
 Snow and ice have a reflectance of 90% that is
particularly high at high latitudes, where the majority of
the earth's glacial ice and sea ice formed.
 Dust in the atmosphere both reflects and absorbs
incoming solar radiation. Reflection increase the
planetary albedo, while absorption heats the upper
atmosphere. Both processes reduce the amount of solar
radiation reaching the lower atmosphere, leading to
cooler air closer to the ground.
The Moon
 Precession displaces the moon relative to the solar equator
over an 18.6 year cycle.
 Only the 18.6 year lunar tide and 11 year sunspot cycles
dominate rainfall.
 Historical trends since 1657 indicate that the united states
great plains was locked into drought shortly after peaks in
the maximum lunar cycle.

The latest peak in 1991 did not lead to subsequent
drought, but to some of the severest flooding of the
Mississippi River ever recorded.
 Droughts in the regions of the northern hemisphere affected
by the lunar tide, are controlled by resonance of the
planetary Rossby wave that is locked topographically into
position by the Tibetan Plateau and Rocky mountains.
Human Activity
 There is no doubt human activity alters the climate.
 Desertification is a complex process which climatic
change is probably the dominant factor and human
activities play a relatively minor part. (it was argued that
desertification at back then was the result of human
activity).
 The most significant cause of climate change is emission
of greenhouse gases such as CO2, into the atmosphere
from human activities.
 In the U.S. most emission result from using energy. Net
emissions are large even though some land uses actually
remove GHS from the air.
Video
 http://www.youtube.com/watch?v=mX3pHD7NH58&feat
ure=player_embedded#!
Conclusion
 Deglaciation is initially driven by the insolation effects of
the short-term Milankovitch cycles, superimposed upon
the longer eccentricity cycle.
 The global effect of volcanic eruptions upon
temperatures also depends upon the location, nature
and type of explosion.
 There is a universal agreement that increased solar
activity during the Holocene led to increased global air
temperatures.
 Solar activity is predicted to increase in the early part of
the 21st century with any enhanced, anthropogenic
greenhouse warming effect.
Works Cited

Bryant, Edward. "Causes of Climate Change." Climate Process and Change.
Cambridge: Cambridge UP, 1997. 97-115. Print.

Burroughs, William James. "The Causes of Climate Change." Climate Change:
a Multidisciplinary Approach. Cambridge: Cambridge UP, 2001. 201-38. Print.

"Milankovitch Cycles." Homepages at Montana.edu. Web. 16 Nov. 2010.
<http://www.homepage.montana.edu/~geol445/hyperglac/time1/milankov.ht
m>.

Pidwirny, M. (2006). "Causes of Climate Change". Fundamentals of Physical
Geography, 2nd Edition. Date Viewed.
http://www.physicalgeography.net/fundamentals/7y.html

"Plate Tectonics and Glacier Formation." Homepages at Montana.edu. Web. 16
Nov. 2010.
<http://www.homepage.montana.edu/~geol445/hyperglac/time1/tectonics.ht
m>.

Ritter, Michael. "Glaciation." University of Wisconsin-Stevens Point. Web. 16
Nov. 2010.
<http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/glacial_systems/
glaciation_causes.html>.

Rosenberg, Matt. "Milankovitch Cycles - Overview of Milankovitch Cycles."
Geography Home Page - Geography at About.com. Web. 16 Nov. 2010.
<http://geography.about.com/od/learnabouttheearth/a/milankovitch.htm>.