September 13, 2010

Is only greenhouse gas emission responsible?

The mean temperature of the world has been rising, snow in the hemisphere and even on mount Everest is melting, sea level is rising, salt water intrusion is reducing the availability of fresh water, coastal region is facing more and frequent cyclones and storm surges. The main cause of these changes is the increase in global temperature due to increased use of fossil fuel throughout the world especially in the developed countries.
It is a very simple equation that we, the human beings are using more and more fossil fuel, emitting huge amount of greenhouse gases that trap the sun's temperature in the earth atmosphere and consequently global temperature is rising and causing climate change which will cause a devastating situation for mankind in the early future.
The earth's position with respect to the sun over time affects its climate. During its annual circuit around the sun, the earth's present elliptical orbit brings it closest to the sun in January (perihelion), and carries it farthest away in July (aphelion). The planet receives about 6% more solar energy in January than in July. The Earth's axis, a line through the poles, is tilted 23.5° with respect to the sun. Consequently, the sun's rays strike the northern hemisphere most directly on June 21st (the summer solstice) and the southern hemisphere most directly on December 21st (the winter solstice).
The equinoxes, on April 21st and September 21st, mark the dates when the sun shines directly on the equator, and day and night are of the same length around the globe. Orbital geometry and axial tilt together determine the earth's pattern of seasons. Variations in this astronomical geometry would cause climatic variations.
The Earth's axial tilt varies between 21.5° and 24.5° with a 41,000 year periodicity (currently decreasing: 24.049 in 3300 BC, 23.443 in 1973, 23.439 in 2000), while the direction of the tilt gradually undergoes precession, moving in a slow circle over a period of about 25,800 years. However, other factors may change the axial tilt of earth (and of other planets).
Recent study concludes that the known wobbles in earth's rotation caused global ice levels to reach their peak about 26,000 years ago, stabilize for 7,000 years and then begin melting 19,000 years ago, eventually bringing to an end the last ice age. The melting was first caused by more solar radiation, not changes in carbon dioxide levels or ocean temperatures. Solar radiation triggered it. There were also changes in atmospheric carbon dioxide levels and ocean circulation, but those happened later and amplified a process that had already begun. The researchers used an analysis of 6,000 dates and locations of ice sheets to define, with a high level of accuracy, when ice started to melt. In doing this, they confirmed a theory that was first developed more than 50 years ago that pointed to small but definable changes in earth's rotation as the trigger for ice age.
The Sahara and Arabia were transformed abruptly from fertile land covered with shrubs and grases into a parched desert in a "brutal" period of climatic change lasting 400 years, scientists have found. For once, humans were not to blame: the cause was not farming or overgrazing, as is usually thought. Scientists reckon that the Sahara began to turn into a desert after the earth underwent one of its periodic changes in orientation, starting 9,000 and finishing about 6,000 years ago. Its tilt lessened from 24.14 degrees off vertical to its present 23.45 degrees, while the time when the planet is closest to the sun shifted gradually from July to January.
Geological changes on the earth's surface can also affect global climate. The distribution of continental landmasses and ocean basins affects the pattern of global atmospheric and oceanographic circulation. The collision of the Indian subcontinent with Asia, and formation of the Himalayan mountain range about 40 million years ago is an example of a plate tectonic event that caused significant climate change. The Himalayas obstruct equatorial winds and ocean currents, and contribute to major climatic phenomena, namely the monsoon seasons of southern Asia and the Indian Ocean.
Quakes can shift the orientation of earth's axis because they move large sections of the crust and subsequently unbalance the planet. Over the course of millions of years, the motion of tectonic plates reconfigures global land and ocean areas. This can affect both global and local patterns of climate and atmosphere-ocean circulation. A recent example of tectonic control on ocean circulation is the formation of the Isthmus of Panama about 5 million years ago, which shut off direct mixing of the Atlantic and the Pacific oceans.
The magnitude 9.1 Sumatran Earthquake in 2004 that generated an Indian Ocean tsunami shortened the day by 6.8 microseconds and shifted the axis by about 2.3 milliarcseconds. Initial U.S. Geological Survey data from the quake and its dozens of powerful aftershocks indicate that some 740 miles of the boundary between the India plate and the Burma plate slipped an average of 15 meters and that the sea floor thrust up several meters. It is difficult to determine the total mass of the crust that shifted because the movement was irregular, but when so much of the earth moves so far, the wobble of its axis will jog slightly, too.
In a demonstration of the satellites' sensitivity to minute changes in earth's mass, the science team reported that the satellites were able to measure the deformation of the earth's crust caused by the December 2004 Sumatra earthquake. That quake changed earth's gravity by one part in a billion. The Richter scale 9.0 magnitude temblor that struck 250 kilometers (155 miles) southeast of Sumatra Island may have moved small islands as much as 20 meters (66 feet). Based on seismic modeling, some of the smaller islands off the southwest coast of Sumatra may have moved to the southwest by about 20 meters. That is a lot of slip. The northwestern tip of the Indonesian territory of Sumatra may also have shifted to the southwest by around 36 meters (120 feet). In addition, the energy released as the two sides of the undersea fault slipped against each other made the earth wobble on its axis).
The magnitude-8.8 earthquake that rocked the west coast of Chile was violent enough to move the city of Concepcion at least 10 feet to the west and the capital, Santiago, about 11 inches to the west-southwest, researchers said. Santa Maria Island off the coast near Concepcion, Chile's second-largest city, may have been raised 2 meters (6 feet) as a result of the quake. The rocks there show evidence pointing to past earthquakes shifting the island upward in the past. The quake also shifted other parts of South America, as far apart as the Falkland Islands and Fortaleza, Brazil.
The Haitian earthquake may have originated from movement along the fault between the North American and Caribbean tectonic plates. When the movement of earth caused by the earthquake changed the distribution of mass, this may have affected the magnitude of force that affects the earth's angular velocity which caused a change in precession.
So, it is really very difficult to say that only emission of green house gas is causing global temperature changes. But it's obvious that it has contribution in the global climate change. But there must be other astronomical, physical and chemical factors behind the global climate change as well. Earth is going through major changes, indeed.From

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