Climate change is a change in the statistical distribution of weather patterns when that change lasts for an extended period of time (i.e., decades to millions of years). Climate change may refer to a change in average weather conditions, or in the time variation of weather around longer-term average conditions (i.e., more or fewer extreme weather events). Climate change is caused by factors such as biotic processes, variations in solar radiation received by Earth, plate tectonics, and volcanic eruptions. Certain human activities have also been identified as significant causes of recent climate change, often referred to as global warming.[1] Factors that can shape climate are called climate forcings or forcing mechanisms.[5] These include processes such as variations in solar radiation, variations in the Earths orbit, variations in the albedo or reflectivity of the continents and oceans, mountain-building and continental drift and changes in greenhouse gas concentrations. There are a variety of climate change feedbacks that can either amplify or diminish the initial forcing. Some parts of the climate system, such as the oceans and ice caps, respond more slowly in reaction to climate forcings, while others respond more quickly. There are also key threshold factors which when exceeded can produce rapid change. Scientists generally define the five components of earths climate system to include atmosphere, hydrosphere, cryosphere, lithosphere (restricted to the surface soils, rocks, and sediments), and biosphere.[6] Natural changes in the climate system (internal forcings) result in internal climate variability.[7] Examples include the type and distribution of species, and changes in ocean currents. The ocean is a fundamental part of the climate system, some changes in it occurring at longer timescales than in the atmosphere, massing hundreds of times more and having very high thermal inertia (such as the ocean depths still lagging today in temperature adjustment from the Little Ice Age).[clarification needed][8] Life affects climate through its role in the carbon and water cycles and such mechanisms as albedo, evapotranspiration, cloud formation, and weathering.[9][10][11] Examples of how life may have affected past climate include: glaciation 2.3 billion years ago triggered by the evolution of oxygenic photosynthesis,[12][13] glaciation 300 million years ago ushered in by long-term burial of decomposition-resistant detritus of vascular land plants (forming coal),[14][15] termination of the Paleocene-Eocene Thermal Maximum 55 million years ago by flourishing marine phytoplankton,[16][17] reversal of global warming 49 million years ago by 800,000 years of arctic azolla blooms,[18][19] and global cooling over the past 40 million years driven by the expansion of grass-grazer ecosystems.[20][21] Life affects climate through its role in the carbon and water cycles and such mechanisms as albedo, evapotranspiration, cloud formation, and weathering.[9][10][11] Examples of how life may have affected past climate include: glaciation 2.3 billion years ago triggered by the evolution of oxygenic photosynthesis,[12][13] glaciation 300 million years ago ushered in by long-term burial of decomposition-resistant detritus of vascular land plants (forming coal),[14][15] termination of the Paleocene-Eocene Thermal Maximum 55 million years ago by flourishing marine phytoplankton,[16][17] reversal of global warming 49 million years ago by 800,000 years of arctic azolla blooms,[18][19] and global cooling over the past 40 million years driven by the expansion of grass-grazer ecosystems.[20][21] The Sun is the predominant source of energy input to the Earth. Both long- and short-term variations in solar intensity are known to affect global climate. Three to four billion years ago the sun emitted only 70% as much power as it does today. If the atmospheric composition had been the same as today, liquid water should not have existed on Earth. However, there is evidence for the presence of water on the early Earth, in the Hadean[26][27] and Archean[28][26] eons, leading to what is known as the faint young Sun paradox.[29] Hypothesized solutions to this paradox include a vastly different atmosphere, with much higher concentrations of greenhouse gases than currently exist.[30] Over the following approximately 4 billion years, the energy output of the sun increased and atmospheric composition changed. The Great Oxygenation Event – oxygenation of the atmosphere around 2.4 billion years ago – was the most notable alteration. Over the next five billion years the suns ultimate death as it becomes a red giant and then a white dwarf will have large effects on climate, with the red giant phase possibly ending any life on Earth that survives until that time. The eruptions considered to be large enough to affect the Earths climate on a scale of more than 1 year are the ones that inject over 0.1 Mt of SO2 into the stratosphere.[40] This is due to the optical properties of SO2 and sulfate aerosols, which strongly absorb or scatter solar radiation, creating a global layer of sulfuric acid haze.[41] On average, such eruptions occur several times per century, and cause cooling (by partially blocking the transmission of solar radiation to the Earths surface) for a period of a few years. The eruption of Mount Pinatubo in 1991, the second largest terrestrial eruption of the 20th century, affected the climate substantially, subsequently global temperatures decreased by about 0.5 °C (0.9 °F) for up to three years.[42][43] Thus, the cooling over large parts of the Earth reduced surface temperatures in 1991-93, the equivalent to a reduction in net radiation of 4 watts per square meter.[44] The Mount Tambora eruption in 1815 caused the Year Without a Summer.[45] Much larger eruptions, known as large igneous provinces, occur only a few times every fifty - hundred million years - through flood basalt, and caused in Earth past global warming and mass extinctions
Posted on: Sun, 12 Oct 2014 10:42:57 +0000
Trending Topics
Recently Viewed Topics
© 2015