Effects of global warming.docx

1、Effects of global warmingEffects of global warmingFrom Wikipedia, the free encyclopediaThis article is about (primarily) effects during the 21st century. For longer term effects, see Long-term effects of global warming.The various effects of climate change pose risks that increase with global warmin

2、g (i.e., increases in the Earths global mean temperature).12 The IPCC (2001d1 and 2007d)3 has organized many of these risks into five reasons for concern: threats to endangered species and unique systems, damages from extreme climate events, effects that fall most heavily on developing countries and

3、 the poor within countries, global aggregate impacts (i.e., various measurements of total social, economic and ecological impacts),34 and large-scale high-impact events. The above burning embers diagram was produced by the IPCC in 2001. A later revision of the diagram, published in 2009, but not app

4、roved by the IPCC, shows increased risks.5This article is about the effects of global warming and climate change. The effects, or impacts, of climate change may be physical, ecological, social or economic. Evidence of observed climate change includes the instrumental temperature record, rising sea l

5、evels, and decreased snow cover in the Northern Hemisphere.6 According to the Intergovernmental Panel on Climate Change (IPCC, 2007a:10), most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in human greenhouse gas concen

6、trations. It is predicted that future climate changes will include further global warming (i.e., an upward trend in global mean temperature), sea level rise, and a probable increase in the frequency of some extreme weather events. Signatories of the United Nations Framework Convention on Climate Cha

7、nge have agreed to implement policies designed to reduce their emissions of greenhouse gases.DefinitionsIn this article, the phrase “climate change” is used to describe a change in the climate, measured in terms of its statistical properties, e.g., the global mean surface temperature.7 In this conte

8、xt, “climate” is taken to mean the average weather. Climate can change over period of time ranging from months to thousands or millions of years. The classical time period is 30 years, as defined by the World Meteorological Organization. The climate change referred to may be due to natural causes, e

9、.g., changes in the suns output, or due to human activities, e.g., changing the composition of the atmosphere.8 Any human-induced changes in climate will occur against the “background” of natural climatic variations (see attribution of recent climate change for more information).In this article, the

10、 phrase “global warming” refers to the change in the Earths global average surface temperature.9 Measurements show a global temperature increase of 1.4F (0.78C) between the years 1900 and 2005. Global warming is closely associated with a broad spectrum of other climate changes, such as increases in

11、the frequency of intense rainfall, decreases in snow cover and sea ice, more frequent and intense heat waves, rising sea levels, and widespread ocean acidification.10Temperature changesGlobal mean surface temperature difference from the average for 18802009This article breaks down some of the impact

12、s of climate change according to different levels of future global warming. This way of describing impacts has, for instance, been used in the IPCCs Assessment Reports on climate change.11 The instrumental temperature record shows global warming of around 0.6 C over the entire 20th century.12 The fu

13、ture level of global warming is uncertain, but a wide range of estimates (projections) have been made.13 The IPCCs SRES scenarios have been frequently used to make projections of future climate change.14:22-24 Climate models using the six SRES marker scenarios suggest future warming of 1.1 to 6.4 C

14、by the end of the 21st century (above average global temperatures over the 1980 to 1999 time period).15 The range in temperature projections partly reflects different projections of future social and economic development (e.g., economic growth, population level, energy policies), which in turn affec

15、ts projections of greenhouse gas (GHG) emissions. The range also reflects uncertainty in the response of the climate system to past and future GHG emissions (measured by the climate sensitivity).The projected rate of warming under these scenarios would very likely be without precedent during at leas

16、t the last 10,000 years (see footnote 1).16 The most recent warm period comparable to these projections was the mid-Pliocene, around 3 million years ago.17 At that time, models suggest that mean global temperatures were about 23 C warmer than pre-industrial temperatures.18Physical impactsMain articl

17、e: Physical impacts of climate changeKey climate indicators that show global warming.19:2-3Working Group Is contribution to the IPCC Fourth Assessment Report, published in 2007, concluded that warming of the climate system was unequivocal.20 This was based on the consistency of evidence across a ran

18、ge of observed changes, including increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.21Human activities have contributed to a number of the observed changes in climate.22 This contribution has principally been through the b

19、urning of fossil fuels, which has led to an increase in the concentration of GHGs in the atmosphere.23 Another human influence on the climate are sulfur dioxide emissions, which are a precursor to the formation of sulfate aerosols in the atmosphere.24Human-induced warming could potentially lead to s

20、ome impacts that are abrupt or irreversible (see the section on Abrupt or irreversible changes).1525 The probability of warming having unforeseen consequences increases with the rate, magnitude, and duration of climate change.26Radiative forcingThe effect of human activities on the climate system ca

21、n be measured by radiative forcing: Energy is constantly flowing into the atmosphere in the form of sunlight that always shines on half of the Earths surface.27 Some of this sunlight is reflected back to space and the rest is absorbed by the planet. Some energy from the Earth is also radiated back o

22、ut into space as invisible infrared light. Radiative forcing is a measure of the energy flowing into the Earth-atmosphere system, minus the energy flowing out. A positive radiative forcing will tend to warm the climate, while a negative forcing will tend to cool the climate.28 Anthopogenic forcing (

23、i.e., the radiative forcing due to human activites) was estimated to have been positive in the year 2005.28 This is relative to the estimated forcings at the start of the industrial era, taken as the year 1750. Anthropogenic forcing of the climate has likely to contributed to a number of observed ch

24、anges, including sea level rise, changes in climate extremes (such as warm and cold days), declines in Arctic sea ice extent, and to glacier retreat.22Effects on weatherObservations show that there have been changes in weather.29 As climate changes, the probabilities of certain types of weather even

25、ts are affected.Changes have been observed in the amount, intensity, frequency, and type of precipitation.14:18 Widespread increases in heavy precipitation have occurred, even in places where total rain amounts have decreased. IPCC (2007d) concluded that human influences had, more likely than not (g

26、reater than 50% probability, based on expert judgement),30 led to an increase in the frequency of heavy precipitation events.31 Projections of future changes in precipitation show overall increases in the global average, but with substantial shifts in where and how precipitation falls.14:24 Climate

27、models tend to project increasing precipitation at high latitudes and in the tropics (e.g., the south-east monsoon region and over the tropical Pacific) and decreasing precipitation in the sub-tropics (e.g., over much of North Africa and the northern Sahara).32Evidence suggests that, since the 1970s

28、, there have been substantial increases in the intensity and duration of tropical storms and hurricanes.33 Models project a general tendency for more intense but fewer storms outside the tropics.14:24Accumulated cyclone energy in the Atlantic Ocean and the sea surface temperature difference which in

29、fluences such, measured by the U.S. NOAA.Extreme weatherSee also: Extreme weather, Tropical cyclone#Global warming,and List of Atlantic hurricane recordsSince the late 20th century, changes have been observed in the trends of some extreme weather and climate events, e.g., heat waves.34 Human activit

30、ies have, with varying degrees of confidence, contributed to some of these observed trends. Projections for the 21st century suggest continuing changes in trends for some extreme events. Solomon et al. (2007), for example, projected the following likely (greater than 66% probability, based on expert

31、 judgement)30 changes:34 an increase in the areas affected by drought; increased tropical cyclone activity; and increased incidence of extreme high sea level (excluding tsunamis).Projected changes in extreme events will have predominantly adverse impacts on ecosystems and human society.3536Glacier r

32、etreat and disappearanceMain article: Retreat of glaciers since 1850A map of the change in thickness of mountain glaciers since 1970. Thinning in orange and red, thickening in blue.IPCC (2007a:5) found that, on average, mountain glaciers and snow cover had decreased in both the northern and southern hemispheres.20 This widespread decrease in glaciers and ice caps had contributed to observed sea level rise. With very high or high confidence (see footnote 2), IPCC (2007b37