Caus of climate change交通事故流程
悲催的生活The earth's climate is dynamic and always changing through a natural cycle. What the world is more worried about is that the changes that are occurring today have been speeded up becau of man's activities. The changes are being studied by scientists all over the world who are finding evidence from tree rings, pollen samples, ice cores, and a diments. The caus of climate change can be divided into two categories - tho that are due to natural caus and tho that are created by man.
Natural caus
There are a number of natural factors responsible for climate change. Some of the more prominent ones are continental drift, volcanoes, ocean currents, the earth's tilt, and comets and meteorites. Let's look at them in a little detail.
胳膊的英文Continental drift
You may have noticed something peculiar about South America and Africa on a map of the
world - don't they em to fit into each other like pieces in a jigsaw puzzle?
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About 200 million years ago they were joined together! Scientists believe that back then, the earth was not as we e it today, but the continents were all part of one large landmass. Proof of this comes from the similarity between plant and animal fossils and broad belts of rocks found on the eastern coastline of South America and western coastline of Africa, which are now widely parated by the Atlantic Ocean. The discovery of fossils of tropical plants (in the form of coal deposits) in Antarctica has led to the conclusion that this frozen land at some time in the past, must have been situated clor to the equator, where the climate was tropical, with swamps and plenty of lush vegetation.
一什么汗水The continents that we are familiar with today were formed when the landmass began gradually drifting apart, millions of years back. This drift also had an impact on the climate becau it changed the physical features of the landmass, their position and the position of water bodies. The paration of the landmass changed the flow of ocean currents a
nd winds, which affected the climate. This drift of the continents continues even today; the Himalayan range is rising by about 1 mm (millimeter) every year becau the Indian land mass is moving towards the Asian land mass, slowly but steadily.
中都草原Volcanoes
When a volcano erupts it throws out large volumes of sulphur dioxide (SO2), water vapour, dust, and ash into the atmosphere. Although the volcanic activity may last only a few days, yet the large volumes of gas and ash can influence climatic patterns for years. Millions of tonnes of sulphur dioxide gas can reach the upper levels of the atmosphere (called the stratosphere) from a major eruption. The gas and dust particles partially block the incoming rays of the sun, leading to cooling. Sulphur dioxide combines with water to form tiny droplets of sulphuric acid. The droplets are so small that many of them can stay aloft for veral years. They are efficient reflectors of sunlight, and screen the ground from some of the energy that it would ordinarily receive from the sun. Winds in the upper levels of the atmopshere, called the stratosphere, carry the aerosols r
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apidly around the globe in either an easterly or westerly direction. Movement of aerosols north and south is always much slower. This should give you some idea of the ways by which cooling can be brought about for a few years after a major volcanic eruption.
Mount Pinatoba, in the Philippine islands erupted in April 1991 emitting thousands of tonnes of gas into the atmosphere. Volcanic eruptions of this magnitude can reduce the amount of solar radiation reaching the Earth's surface, lowering temperatures in the lower levels of the atmosphere (called the troposphere), and changing atmospheric circulation patterns. The extent to which this occurs is an ongoing debate.
Another striking example was in the year 1816, often referred to as "the year without a summer." Significant weather-related disruptions occurred in New England and in Western Europe with killing summer frosts in the United States and Canada. The strange phenomena were attributed to a major eruption of the Tambora volcano in Indonesia, in 1815.
The earth's tilt
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The earth makes one full orbit around the sun each year. It is tilted at an angle of 23.5° to the perpendicular plane of its orbital path. For one half of the year when it is summer, the northern hemisphere tilts towards the sun. In the other half when it is winter, the earth is tilted away from the sun. If there was no tilt we would not have experienced asons. Changes in the tilt of the earth can affect the verity of the asons - more tilt means warmer summers and colder winters; less tilt means cooler summers and milder winters.
The Earth's orbit is somewhat elliptical, which means that the distance between the earth and the Sun varies over the cour of a year. We usually think of the earth's axis as being fixed, after all, it always ems to point toward Polaris (also known as the Pole Star and the North Star). Actually, it is not quite constant: the axis does move, at the rate of a little more than a half-degree each century. So Polaris has not always been, and will not always be, the star pointing to the North. When the pyramids were built, around 2500 BC, the pole was near the star Thuban (Alpha Draconis). This gradual change in the direction of the earth's axis, called precession is responsible for changes in the climate.
Ocean currents
The oceans are a major component of the climate system. They cover about 71% of the Earth and absorb about twice as much of the sun's radiation as the atmosphere or the land surface. Ocean currents move vast amounts of heat across the planet - roughly the same amount as the atmosphere does. But the oceans are surrounded by land mass, so heat transport through the water is through channels.
