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 What is climate change?

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Starflower



Antal inlägg : 154
Registration date : 07-10-07

InläggRubrik: Sv: What is climate change?   sön okt 07, 2007 1:42 pm

WHAT IS CLIMATE CHANGE?

Climate Change is a change occurring in the climate during a period of time that can range from decades all the way up to centuries. The term refers to changes caused both by nature and changes that are caused by human beings. The term “climate variability” refers to shorter periods ranging from years to decades which show climate fluctuations such as the ones caused by the “El Niño” phenomenon.

The United Nations Framework Convention on Climate Change (UNFCCC) defines this phenomenon as: "a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods”. In other words, the UNFCCC is using the term climate change to refer to changes produced by the activities of human beings.

FACTORS AFFECTING GLOBAL CLIMATE

There are many factors of both natural and human origin that determine the Earth’s climate.

The Sun is the primary source of energy controlling the status of weather and climate on the Earth. Radiation coming from the Sun is intercepted by the Earth, and one third of this solar radiation is reflected back into space. The other two thirds are absorbed by different parts of the climate system: the atmosphere, the oceans, glacial areas, soils and different kinds of life.

The Earth also sends its energy back into space in the form of long wavelength radiation. Some of this energy is re-absorbed and is therefore kept on the Earth through a process known as the Greenhouse Effect. The rest of this energy is lost in space.

There is a delicate balance between this radiation that is leaving and solar energy that is arriving. Any change in the factors affecting this balance of energy that is coming and going, or in the actual distribution of energy, can change the Earth’s climate. Factors affecting climate are classified among:

* Natural Factors
* Human Factors

NATURAL FACTORS AFFECTING CLIMATE

There have been changes in climate throughout the Earth’s history. The Ice Age and some other warmer periods are examples of this. Some of these changes have been on a global scale, while others have been on a regional or hemispheric scale. The natural factors causing climate changes are described below:
Changes in the Production of Solar Energy

The amount of energy emitted by the Sun is not constant. There is evidence that the amount of energy produced by the Sun varies over an 11 year period, which affects the Earth’s temperature. It should also be mentioned that solar periods may be shorter or longer.
Changes in Distance and Position of the Earth with Respect to the Sun

Slow variations in the Earth’s distance and position with respect to the Sun change the place and time at which solar energy is delivered to the planet. This affects the amount of energy that is reflected and absorbed by the Earth, and determines the seasons.

Changes in the Earth’s Angle of Inclination

Slight variations in the Earth’s angle of inclination with respect to the polar axis can cause variations in the amount of solar energy reaching the Earth’s surface. It is believed that such variations were a factor at the beginning of the Ice Age.
The Greenhouse Effect

Solar energy that is able to get through the atmosphere serves to heat the Earth’s surface. This energy is then released from the surface toward space as infrared radiation. The greenhouse gases (water vapor, carbon dioxide, methane, nitrous oxides, ozone, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride) that are present in the atmosphere absorb a large proportion of the infrared radiation emitted by the Earth, thus preventing this energy from escaping directly from the Earth’s surface into space. This radiation is then released into the atmosphere by air currents, evaporation, rain, etc. If the surface of the Earth could freely irradiate energy, our planet would be a cold, lifeless place, so therefore the greenhouse gases help maintain a proper temperature for life on Earth. When the atmosphere’s capability for absorbing infrared radiation becomes increased due to the presence of an excess of greenhouse gases, there is an alteration in climate because the balance between energy entering and energy leaving the atmosphere is upset. Global overheating is then caused when infrared radiation is not able to leave the Earth. According to the United Nations Environment Program (UNEP), if greenhouse gases continue to be emitted at the current rate, during the next decade the Earth will cease to emit 2% of its energy toward space, which is the same as retaining the energy content of 3 million tons of petroleum per minute.

HUMAN FACTORS AFFECTING CLIMATE

Greenhouse Gases

There are different greenhouse gases. The most common one that represents over 60% of the total amount of these gases is carbon dioxide (CO2). Carbon dioxide is mainly generated by the use of fossil fuels such as petroleum, gas and coal, and therefore the energy sector is the main contributor to global warming. Industries are generating 21% of this gas, while electric power generation is emitting 36% and transportation is contributing with 27% of total CO2 emissions coming from combustion processes.[i]

The second most important gas is methane (CH4). Methane is mainly generated by agricultural and livestock activities, and amounts to between 15 and 20% of the planet’s greenhouse gas total.

The United States is the largest producer of greenhouse gases on the American continent, and it is also at the top of the world’s list of emitters, with a production of 5,324 million tons of CO2 emitted in 1996. Canada is in second place in emissions with 469 million tons emitted and is followed by Mexico with 342 million tons emitted for the same year.[ii] Therefore, the northern part of the continent is the largest generator of emissions, but there is a big difference between Mexico, which is emitting approximately 2% of the total and the United States, which is emitting over 20%. On the other hand, there are countries like Costa Rica that are emitting close to 4 million tons annually of CO2, which are also vital due to their wealth of forest resources.
Land Use Change

As human beings continue to turn the forests and jungles into lands for agriculture and livestock raising or to pave them over with asphalt and concrete, the way in which the Earth’s surface reflects sunlight and allows heat to escape will continue to become substantially altered. Forests are also absorbers of CO2 and generators of oxygen, and between 20 and 50 times more carbon is absorbed by unit of area in forests than on lands used for agricultural purposes[iii].
Atmospheric Aerosols

Human beings are filling the atmosphere with large amounts of fine particles (aerosols) coming from both agricultural and industrial activities. Although most of these aerosols are quickly removed by gravity and rain, they are affecting the radiation balance in the atmosphere.

CLIMATE TRENDS

A review of temperature records shows that the Earth has been heating up by an average of 0.5° C during the last 100 years. This warming seems to have continued up to the forties. Afterwards, there was a moderate cooling trend that continued up to the first half of the seventies, followed by another continuous warming from the eighties on. The eleven hottest years of the 20th century have been 1981, 1983, 1987, 1989, 1990, 1991, 1994, 1995, 1996, 1998 and 1999. During this period there have also been changes in several of the Earth’s regions. For example, there has been greater warming during the winter and spring in areas of middle latitude. Cooling has also been recorded in the North Atlantic area. Precipitation has increased in Northern Hemisphere latitudes, especially during the colder seasons.

This steady trend in global warming has been growing due to the greenhouse effect and aerosols. However, this variation in temperature could be within acceptable limits and could be considered to be a natural variation.
Scientific Evidence

According to the United Nations Intergovernmental Panel on Climate Change, climate change caused by “greenhouse” gases has brought about the following effects during the most recent years of industrial production:

The Earth’s median temperature has increased by 0.5° since the last century, which has caused changes at the Earth’s surface..

Sea level has gone up about 30 cms. as a result of the thermal expansion of oceans and the melting of polar ice.

According to the Panel, made up of members of the United Nations Environment Program and the World Meteorological Association, there was a consensus in the following predictions:

There is a recognition that the problem does exist. Although exact predictions cannot be precisely calculated, there are alarming estimates that have resulted in this problem being recognized by 165 countries.

If greenhouse gases continue to be emitted at the same increasing rate, it is estimated that the temperature will go up by between 1° and 4° C in the next 100 years.

A temperature increase of this magnitude would cause sea level increases ranging between 50 and 95 centimeters, flooding large portions of coastal areas.

Climate change also causes droughts, storms, heat waves, changes in rainfall precipitation and desertification.
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