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Assignment on
Effects of Global warming
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This assignment is about the current change in Earth's climate. For general discussion of how the
climate can change, see Climate change . For other uses, see Global warming (disambiguation) .
Global mean land-ocean temperature change from 1880–2012, relative to the 1951–1980 mean.
The black line is the annual mean and the red line is the 5-year running mean . The green bars
show uncertainty estimates. Source: NASA GISS .
The map shows the 10-year average (2000–2009) global mean temperature anomaly relative to
the 1951–1980 mean. The largest temperature increases are in the Arctic and the Antarctic
Peninsula. Source: NASA Earth Observatory
Fossil fuel related CO 2 emissions compared to five of the IPCC's " SRES " emissions scenarios.
The dips are related to global recessions. Image source: Skeptical Science .
Global warming is the rise in the average temperature of Earth's atmosphere and oceans since
the late 19th century and its projected continuation. Since the early 20th century, Earth's mean
surface temperature has increased by about 0.8 °C (1.4 °F), with about two-thirds of the increase
occurring since 1980. [2] Warming of the climate system is unequivocal, and scientists are more
than 90% certain that it is primarily caused by increasing concentrations of greenhouse gases
produced by human activities such as the burning of fossil fuels and deforestation . [3][4][5][6] These
findings are recognized by the national science academies of all major industrialized nations. [7][A]
Climate model projections were summarized in the 2007 Fourth Assessment Report (AR4) by
the Intergovernmental Panel on Climate Change (IPCC). They indicated that during the 21st
century the global surface temperature is likely to rise a further 1.1 to 2.9 °C (2 to 5.2 °F) for
their lowest emissions scenario and 2.4 to 6.4 °C (4.3 to 11.5 °F) for their highest. [8] The ranges
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of these estimates arise from the use of models with differing sensitivity to greenhouse gas
concentrations . [9][10]
Future warming and related changes will vary from region to region around the globe. The
effects of an increase in global temperature include a rise in sea levels and a change in the
amount and pattern of precipitation , as well a probable expansion of subtropical deserts .
Warming is expected to be strongest in the Arctic and would be associated with the continuing
retreat of glaciers , permafrost and sea ice . Other likely effects of the warming include a more
frequent occurrence of extreme-weather events including heat waves , droughts and heavy
rainfall, ocean acidification and species extinctions due to shifting temperature regimes. Effects
significant to humans include the threat to food security from decreasing crop yields and the loss
of habitat from inundation.
Proposed policy responses to global warming include mitigation by emissions reduction,
adaptation to its effects, and possible future geoengineering . Most countries are parties to the
United Nations Framework Convention on Climate Change (UNFCCC), whose ultimate
objective is to prevent dangerous anthropogenic (i.e., human-induced) climate change . Parties to
the UNFCCC have adopted a range of policies designed to reduce greenhouse gas
emissions [17] :10 [18][19][20] :9 and to assist in adaptation to global warming . Parties to the UNFCCC have
agreed that deep cuts in emissions are required, and that future global warming should be limited
to below 2.0 °C (3.6 °F) relative to the pre-industrial level. Reports published in 2011 by the
United Nations Environment Programme and the International Energy Agency suggest that
efforts as of the early 21st century to reduce emissions may be inadequate to meet the
UNFCCC's 2 °C target.
Observed temperature changes
Main article: Instrumental temperature record
The increase in ocean heat content is much larger than any other store of energy in the Earth’s
heat balance over the two periods 1961 to 2003 and 1993 to 2003, and accounts for more than
90% of the possible increase in heat content of the Earth system during these periods.
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Two millennia of mean surface temperatures according to different reconstructions from climate
proxies , each smoothed on a decadal scale, with the instrumental temperature record overlaid in
black.
The Earth's average surface temperature rose by 0.74±0.18 °C over the period 1906–2005. The
rate of warming over the last half of that period was almost double that for the period as a whole
(0.13±0.03 °C per decade, versus 0.07±0.02 °C per decade). The urban heat island effect is very
small, estimated to account for less than 0.002 °C of warming per decade since 1900. [27]
Temperatures in the lower troposphere have increased between 0.13 and 0.22 °C (0.22 and
0.4 °F ) per decade since 1979, according to satellite temperature measurements . Climate proxies
show the temperature to have been relatively stable over the one or two thousand years before
1850, with regionally varying fluctuations such as the Medieval Warm Period and the Little Ice
Age . [28]
The warming that is evident in the instrumental temperature record is consistent with a wide
range of observations, as documented by many independent scientific groups. [29] Examples
include sea level rise ( water expands as it warms), [30] widespread melting of snow and ice , [31]
increased heat content of the oceans , [29] increased humidity , [29] and the earlier timing of spring
events, [32] e.g., the flowering of plants . [33] The probability that these changes could have occurred
by chance is virtually zero. [29]
Recent estimates by NASA 's Goddard Institute for Space Studies (GISS) and the National
Climatic Data Center show that 2005 and 2010 tied for the planet's warmest year since reliable,
widespread instrumental measurements became available in the late 19th century, exceeding
1998 by a few hundredths of a degree. [34][35][36] Estimates by the Climatic Research Unit (CRU)
show 2005 as the second warmest year, behind 1998 with 2003 and 2010 tied for third warmest
year, however, "the error estimate for individual years ... is at least ten times larger than the
differences between these three years." [37] The World Meteorological Organization (WMO)
statement on the status of the global climate in 2010 explains that, "The 2010 nominal value of
+0.53 °C ranks just ahead of those of 2005 (+0.52 °C) and 1998 (+0.51 °C), although the
differences between the three years are not statistically significant..." [38]
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NOAA graph of Global Annual Temperature Anomalies 1950–2012, showing the El Niño-
Southern Oscillation
Temperatures in 1998 were unusually warm because global temperatures are affected by the El
Niño-Southern Oscillation (ENSO), and the strongest El Niño in the past century occurred during
that year. [39] Global temperature is subject to short-term fluctuations that overlay long term trends
and can temporarily mask them. The relative stability in temperature from 2002 to 2009 is
consistent with such an episode. [40][41] 2010 was also an El Niño year. On the low swing of the
oscillation, 2011 as an La Niña year was cooler but it was still the 11th warmest year since
records began in 1880. Of the 13 warmest years since 1880, 11 were the years from 2001 to
2011. Over the more recent record, 2011 was the warmest La Niña year in the period from 1950
to 2011, and was close to 1997 which was not at the lowest point of the cycle. [42]
Temperature changes vary over the globe. Since 1979, land temperatures have increased about
twice as fast as ocean temperatures (0.25 °C per decade against 0.13 °C per decade). [43] Ocean
temperatures increase more slowly than land temperatures because of the larger effective heat
capacity of the oceans and because the ocean loses more heat by evaporation. [44] The northern
hemisphere warms faster than the southern hemisphere because it has more land and because it
has extensive areas of seasonal snow and sea-ice cover subject to ice-albedo feedback . [ citation needed ]
Average arctic temperatures have been increasing at almost twice the rate of the rest of the world
in the past 100 years, however arctic temperatures are also highly variable. [45] Although more
greenhouse gases are emitted in the Northern than Southern Hemisphere this does not contribute
to the difference in warming because the major greenhouse gases persist long enough to mix
between hemispheres. [46]
The thermal inertia of the oceans and slow responses of other indirect effects mean that climate
can take centuries or longer to adjust to changes in forcing. Climate commitment studies indicate
that even if greenhouse gases were stabilized at 2000 levels, a further warming of about 0.5 °C
(0.9 °F) would still occur. [47]
Initial causes of temperature changes (external forcings)
Main article: Attribution of recent climate change
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Greenhouse effect schematic showing energy flows between space, the atmosphere, and earth's
surface. Energy exchanges are expressed in watts per square meter (W/m 2 ).
This graph, known as the Keeling Curve , shows the increase of atmospheric carbon dioxide
(CO 2 ) concentrations from 1958–2008. Monthly CO 2 measurements display seasonal oscillations
in an upward trend; each year's maximum occurs during the Northern Hemisphere 's late spring,
and declines during its growing season as plants remove some atmospheric CO 2 .
The climate system can respond to changes in external forcings. [48][49] External forcings can
"push" the climate in the direction of warming or cooling. [50] Examples of external forcings
include changes in atmospheric composition (e.g., increased concentrations of greenhouse
gases ), solar luminosity , volcanic eruptions, and variations in Earth's orbit around the Sun. [51]
Orbital cycles vary slowly over tens of thousands of years and at present are in an overall cooling
trend which would be expected to lead towards an ice age , but the 20th century instrumental
temperature record shows a sudden rise in global temperatures. [52]