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How do human activities contribute to climate change?
Human activities contribute to climate change causing changes in Earth's atmosphere as to the amounts of greenhouse gases, aerosols (small particles) and cloud cover. Most known contribution comes from the combustion of fossil fuels, which releases carbon dioxide gas to atmosphere. Greenhouse gases and aerosols affect climate by altering incoming solar radiation and infrared (thermal) radiation projection, part of the energy balance of the Earth. The variation in atmospheric abundance or properties of these gases and particles can lead to a warming or cooling of the climate system. Since the beginning of the industrial era (about 1750), the overall effect of human activities on climate has been warming cause. The impact of humans on the climate during this era is much higher than that due to known changes in natural sources such as solar changes and volcanic processes.
Greenhouse Gases
Human activities result in emissions bring four major greenhouse gases: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and carbon halo (group of gases containing fluorine, chlorine and bromine). These gases build up in the atmosphere, causing an increase in their concentration with the passage of time. In the industrial era there have been significant increases in these gases (see Figure 1) These increases are attributed to human activities.
• Carbon dioxide has increased due to the use of fuels for transport, heating systems and air conditioning of buildings, cement production and other goods. With deforestation releases CO2 and CO2 uptake of plants is reduced. Carbon dioxide is also released natural processes such as decomposition of vegetable matter.
• Methane has increased as a result of human activities related to agriculture, natural gas distribution and landfills. There are also natural processes in which methane is released, for example in wetlands. Methane concentrations are not currently increasing in the atmosphere because its growth rate declined over the past two decades.
• As a result of human activities also emit nitrous oxide with the use of fertilizers and burning fossil fuels. Natural processes of soils and oceans also release N2O.
• Concentrations of halocarbons have increased mainly due to human activities. Natural processes have also been a small fountain. Among the major halocarbons Chlorofluorocarbons (CFC-11 and as CFC-12), which were used extensively as coolants and other industrial processes before they knew that their presence in the atmosphere cause the depletion of ozone in stratosphere include . High concentrations of chlorofluorocarbons decreases as a result of international regulations designed to protect the ozone layer.
• Ozone is a greenhouse gas that is produced and continuously destroyed in the atmosphere by chemical reactions. In the troposphere, has increased the concentration of ozone as a result of human activities in which gases such as carbon monoxide, hydrocarbons and nitrogen oxides, which react chemically produced ozone is released. As mentioned above, halocarbons released as a result of human activities destroy ozone in the stratosphere and have opened the ozone hole over Antarctica.
• Water vapor is the most abundant and gas present in the atmosphere important greenhouse. However, human activity has only a small direct effect on the amount of water vapor in the atmosphere. Indirectly, humans have the ability to substantially influence on water vapor and climate change. For example, a warmer atmosphere contains more water vapor. Human activities also influence the water vapor through CH4, because the latter undergoes chemical destruction in the stratosphere, thus producing a small amount of water vapor.
• Aerosols are small particles in the atmosphere having a wide range of variation in the concentration, chemical composition and size. Some aerosols are emitted directly into the atmosphere while others are formed from compounds emitted. Aerosols contain compounds that occur naturally and others that are emitted as a result of human activities. The burning of fossil fuels and biomass has increased the percent of aerosols containing sulfur compounds, organic compounds and black (soot) carbon. Human activities such as open-pit mining and industrial processes have increased amounts of dust in the atmosphere. Among the natural mineral dust aerosols are released from the surface of the sea salt aerosols, biogenic emissions from soil and oceans, and dust aerosols and sulfate produced by eruptions volcánicas.Las aerosol particles directly influence radiative and absorption of solar and infrared radiation from the atmosphere forcing. Some aerosols, bring about a positive forcing while others produce negative one. The sum of the direct radiative forcing and all types of aerosols is negative. Indirectly, aerosols results also bring negative radiative forcing due to changes in the properties that cause the nubes.Desde the beginning of the industrial era, human activities have changed the nature of the earth's envelope worldwide , especially through changes in agricultural land, grasslands and forests. They have also modified the reflective properties of ice and snow. In general, it is likely that more solar radiation to the earth's surface is reflected due to human activities. This change results in one negativo.Los forcing planes leave behind a linear tail condensation (condensation trail) in regions where low temperatures and high humidity. Contrails are a form of cirrus reflecting solar radiation and absorbs infrared radiation. The linear contrails aviation operations worldwide have increased cloudiness of Earth and is expected to produce a small positivo.Forzamientos radiative radiative forcing from natural changes arise Natural forcings due to solar changes and explosions eruptions volcanic. The total solar radiation has gradually increased in the industrial era caused a small radiative forcing (see Figure This is in addition to cyclical changes in solar radiation have a cycle of 11 years. Directly Solar energy heats the climate system and can affect also abundant in the atmosphere of some greenhouse gases, such as stratospheric ozone. explosions volcanic eruptions can create a negative forcing of short duration (2-3 years) by the temporary increase that occurs in the sulfate aerosol the stratosphere. Currently, the stratosphere is free of volcanic aerosols since the last major eruption was in 1991 (Pinatubo). differences in estimates of radiative forcing between the present values ​​and the start of the industrial era to changes in solar irradiance and volcanoes are very small compared to the differences in the estimated radiative forcings are the result of human activity. Consequently, in the current atmosphere, the radiative forcing caused by human activity are much more important for the current and future climate change radiative forcing calculated from changes in natural processes.

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