www.v.au/rearch/topics/climate-change/caus
What is climate change?
The Earth’s climate varies over times scales from months through to centuries and beyond. Factors that affect the climate over time-scales from hundreds to millions of years include:
•energy output from the sun,
•variation in the earth’s orbit and the orientation of its axis,
•the greenhou effect of water vapour and other trace gas, •volcanic and meteorite activity and plate tectonics (movement of the continents).
半缘修道半缘君For example, glacial cycles are driven by wobbles in the Earth’s orbit.
Greenhou gas and polar ice sheets respond to this wobble and enhance the warming/cooling cycle of the earth by 2-3°C. Ot her natural phenomena cau variability at decadal and inter-annual scales: changes in a surface temperature, ocean currents and the associated changes in the atmospheric circulations (eg. the El Niño-Southern Oscillation). The resultant changes to the climate from the phenomena are considered to be natural variation.
The term ‘Climate Change’ commonly refers to influences on climate resulting from human practices. Increas in the concentration of so-called greenhou gas in the atmosphere resulting largely from burning of fossil fuels and
deforestation, have led to an obrved and projected warming of the earth, known as the enhanced greenhou effect. It is not easy to distinguish this anthropogenic climate change from the natural variations in the drivers
described above.
The study of the climate and its variations, extremes and shifts is not a new science; Svante Arrhenius suggested in 1896 that burning of fossil fuels might cau an increa in carbon dioxide in the atmosphere and in turn warm the Earth (Pittock 2003). However, the recent succession of unusually warm
怎么分享wifi密码years and extreme climatic events has heightened awareness and climate change is now a mainstream media topic, in recent times moving to headline status. The intensity of interest is placing considerable pressure on the
capacity of the scientific community to respond to the concerns being raid.
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Until very recently much of the media attention centred on the sceptics who put up counter arguments to the existence of climate change, pointing to the 5°C difference in global average temperatures betwe en the glacial and inter-
墨头鱼glacial periods (>10,000 year cycles) as evidence that recent temperature trends are within normal variation (Pittock 2003). The sceptics played a very important role in forcing the scientists to produce evidence of rigorous analysis of their scenarios and projections. If current trends continue, scientists predict temperature ris of up to 5°C o ver the next century, causing major perturbation of natural and human systems.
What caus climate change?
The Earth would be much colder if not for the ‘greenhou’ gas that provide a blanket that warms the atmosphere. Some of the gas in the atmosphere transmit the short-wave radiation from the Sun to the Earth, warming its surface.
Some of this warmth is emitted in the form of long-wave (infrared) radiation from the Earth to the atmosphere and some of the gas in the atmosphere absorb and re-emit radiation of this wavelength, effectively enhancing the warming of the lower atmosphere (Figure 1). The gas are
called greenhou gas becau their effect is similar to the function of a glass greenhou that heats up as infrared radiation is trapped by the glass. The main greenhou gas are water vapour, carbon dioxide, methane and nitrous oxide, all of which occur naturally in the atmosphere.电流磁效应
The enhanced greenhou effect (source: Cooperative Rearch Centre for Greenhou Accounting 2006)
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Water vapour is the major contributor to the greenhou effect. Water vapour concentrations fluctuate regionally due to natural impacts, and human activity
generally does not directly affect water vapour concentrations except at very local scales. However, climate models are now predicting the concentration of water vapour in the upper troposphere may increa in respon to increasing concentrations of other greenhou gas (Steffen 2006). This increa in water vapour could play a key role in amplifying the rate at which the climate warms (Soden et al. 2005).
The gas that contribute directly to the enhanced greenhou effect as a result of anthropogenic activities are carbon dioxide, methane and nitrous oxide emitted from combustion of fossil fuels, deforestation and agriculture, and sulphur hexafluoride, perfluorocarbons and hydrofluorocarbons arising from industrial process. It is the six gas that are controlled under the UN Framework Convention on Climate Change. Some other gas, including carbon monoxide, nitrogen oxides and volatile organic compounds, contribute indirectly to global warming through chemical reactions in the atmosphere. Other emissions, such as sulfate aerosols have a cooling or dimming effect on the climate as they reflect some of the short-wave radiation before it reaches the earth’s surface.
The concentration of CO2 in the atmosphere in 2005 was 379 parts per million (ppm), compared with the pre-industrial value of 280 ppm, and is rising at 1.9 ppm per year (1995-2005 average) (Solomon et al. 2007). The increa in concentration of greenhou gas in the atmosphere has altered the earth's radiative balance, resulting in more of the sun's heat being absorbed and trapped inside the earth's atmosphere, producing global warming. Without mitigation measures, the concentration of CO2 in the atmosphere is predicted to ri to at least 650 ppm and up to 1200 ppm by 2100 (IPCC 2001a), which is expected to increa average global temperature by 1 to 6°C.
Most scientists agree that global warming caud by anthropogenic greenhou gas emissions is one of the most rious environmental problems facing the world today, with far-reaching conquences for all ctors of society. To avert catastrophic impact it is generally agreed that atmospheric CO2 concentration should be constrained to 550 ppm, which is believed will limit the temperature increa to 2°C.
Bibliography
•IPCC (Intergovernmental Panel on Climate Change) 2001a, ‘Climate change 2001: the scientific basis’, in JT Houghton, V Ding, DJ Griggs, M Noguer, PJ van der Linden, X Dai, K Maskell & CA Johnson (eds), Contribution of Working Group I to the third
asssment report of the Intergovernmental Panel on Climate Change, Cambridge University Press, UK.
•Pittock, B (ed) 2003, Climate change: an Australian guide to the science and potential impacts, Australian Greenhou Office
•Soden, BJ, Jackson, DL, Ramaswamy, V, Schwarzkopf, MD & Huang, X 2005, ‘The radiative signature of upper troposphere moistening’, Science, vol. 310, pp. 841-844.鞋子除臭剂
•Solomon, S, Qin, D, Manning, M, Alley, RB, Berntn, T, Bindoff, NL, Chen, Z Chidthaisong, A, Gregory, JM, Hegerl, GC, Heimann, M, Hewitson, B, Hoskins, BJ, Joos, F, Jouzel, J, Kattsov, V, Lohmann, U, Matsuno, T, Molina, M, Nicholls, N,
Overpeck, J, Raga, G, Ramaswamy, V, Ren, J, Rusticucci, M, Somerville, R, Stocker, TF, Whetton, P, Wood RA & Wratt D 2007: Technical Summary. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth
Asssment Report of the Intergovernmental Panel on Climate Change [Solomon, S, Qin, D, Manning, M, Chen, Z, Marquis, M, Averyt, KB, Tignor M & Miller HL (eds.)].
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Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
•Steffen, W. 2006, Stronger Evidence but New Challenges: Climate Change Science 2001-2005, Report to the Department of Environment and Heritage, Australian
Greenhou Office.
