![]() ![]() The gases and dust particles thrown into the atmosphere during volcanic eruptions have influences on climate and cool the planet by shading incoming solar radiation. Under certain circumstances, however, they may cause additional heating, such as the case of black carbon in soot. In general, aerosols have a cooling effect on climate, which partially counterbalances the heating effect of greenhouse gases. Aerosols influence Earth’s climate both directly, by scattering and absorbing sunlight, and indirectly, by altering the reflectivity of clouds. They result mostly from chemical reactions between gaseous air pollutants, rising sand or sea spray, forest fires, agricultural and industrial activities and vehicle exhausts.Īerosols affect many aspects of human health and the environment, visible in the case of strong smog or haze events. Aerosols are small dust particles that float in the atmosphere. The atmosphere also contains small suspended solid and liquid particles. The ozone layer shields us from the harmful effects of excessive UV radiation, which can lead to sunburn, skin cancer and eye damage. ![]() Higher up, in the stratosphere, the ozone layer absorbs solar ultra-violet radiation and affects how much of the Sun's heat is radiated back into space. Ozone in the lower part of the atmosphere acts as a greenhouse gas and is a major pollutant. It does not stay in the atmosphere for very long but plays a key role in our climate and its variability and change. Water vapour is the most abundant greenhouse gas. The main long-lived greenhouse gases are carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). But they are not the only forces at work. This effect is enhanced by increasing greenhouse gas concentrations in the atmosphere due to emissions by human activities such as burning fossil fuels. Without this natural greenhouse effect, the Earth’s average surface temperature would be an inhospitable -18☌ (0☏) instead of the 14☌ (59☏) we experience today. Part of this longwave radiation is absorbed by greenhouse gases which then radiate energy into all directions, including downwards and thereby trapping heat in the atmosphere. The Earth radiates energy at wavelengths much longer than the Sun because it is colder. In total approximately 70% of incoming radiation is absorbed by the atmosphere and the Earth’s surface while around 30% is reflected back to space and does not heat the surface. The Earth absorbs most of the energy reaching its surface, a small fraction is reflected. Solar radiation that is not absorbed or reflected by the atmosphere (for example by clouds) reaches the surface of the Earth.
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