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.
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&feature=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.htm>. • 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.htm>. • 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>.