Globalwarming awareness : climate Change 2007:
The Physical Science Basis
Summary for Policymakers
So now is prouved that globalwarming awareness2007 is a abslolue necessary...
INTRODUCTION
The Working Group I contribution to the IPCC Fourth Assessment Report describes progress inunderstanding of the human and natural drivers of climate change1, observed climate change, climate
processes and attribution, and estimates of projected future climate change. It builds upon past IPCC
assessments and incorporates new findings from the past six years of research. Scientific progress since the
TAR is based upon large amounts of new and more comprehensive data, more sophisticated analyses of
data, improvements in understanding of processes and their simulation in models, and more extensive
exploration of uncertainty ranges.
The basis for substantive paragraphs in this Summary for Policymakers can be found in the chapter
sections specified in curly brackets.
HUMAN AND NATURAL DRIVERS OF CLIMATE CHANGE
Changes in the atmospheric abundance of greenhouse gases and aerosols, in solar radiation and in landsurface properties alter the energy balance of the climate system. These changes are expressed in terms of
radiative forcing2, which is used to compare how a range of human and natural factors drive warming or
cooling influences on global climate. Since the Third Assessment Report (TAR), new observations and
related modelling of greenhouse gases, solar activity, land surface properties and some aspects of aerosols
have led to improvements in the quantitative estimates of radiative forcing.
Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased
markedly as a result of human activities since 1750 and now far exceed pre-industrial values
determined from ice cores spanning many thousands of years (see Figure SPM-1). The global
increases in carbon dioxide concentration are due primarily to fossil fuel use and land-use change,
while those of methane and nitrous oxide are primarily due to agriculture.
• Carbon dioxide
is the most important anthropogenic greenhouse gas (see Figure SPM-2).
The global
atmospheric concentration of carbon dioxide has increased from a pre-industrial value of about 280 ppm to
379 ppm3 in 2005. The atmospheric concentration of carbon dioxide in 2005 exceeds by far the natural
range over the last 650,000 years (180 to 300 ppm) as determined from ice cores. The annual carbon
dioxide concentration growth-rate was larger during the last 10 years (1995 – 2005 average: 1.9 ppm per
year), than it has been since the beginning of continuous direct atmospheric measurements (1960–2005
average: 1.4 ppm per year) although there is year-to-year variability in growth rates.
• The primary source of the increased atmospheric concentration of carbon dioxide since the pre-industrial
period results from fossil fuel use, with land use change providing another significant but smaller
contribution. Annual fossil carbon dioxide emissions4 increased from an average of 6.4 [6.0 to 6.8] 5 GtC
atmospheric concentration of carbon dioxide has increased from a pre-industrial value of about 280 ppm to
379 ppm3 in 2005. The atmospheric concentration of carbon dioxide in 2005 exceeds by far the natural
range over the last 650,000 years (180 to 300 ppm) as determined from ice cores. The annual carbon
dioxide concentration growth-rate was larger during the last 10 years (1995 – 2005 average: 1.9 ppm per
year), than it has been since the beginning of continuous direct atmospheric measurements (1960–2005
average: 1.4 ppm per year) although there is year-to-year variability in growth rates.
• The primary source of the increased atmospheric concentration of carbon dioxide since the pre-industrial
period results from fossil fuel use, with land use change providing another significant but smaller
contribution. Annual fossil carbon dioxide emissions4 increased from an average of 6.4 [6.0 to 6.8] 5 GtC
DIRECT OBSERVATIONS OF RECENT CLIMATE CHANGE
Since the TAR, progress in understanding how climate is changing in space and in time has been gainedthrough improvements and extensions of numerous datasets and data analyses, broader geographical
coverage, better understanding of uncertainties, and a wider variety of measurements. Increasingly
comprehensive observations are available for glaciers and snow cover since the 1960s, and for sea level
and ice sheets since about the past decade. However, data coverage remains limited in some regions.
Warming of the climate system is unequivocal, as is now evident from observations of increases in
global average air and ocean temperatures, widespread melting of snow and ice, and rising global
mean sea level (see Figure SPM-3). {3.2, 4.2, 5.5}
• Eleven of
the
last twelve years (1995 -2006) rank among the 12 warmest years in the
instrumental record of
global surface temperature9 (since 1850). The updated 100-year linear trend (1906–2005) of 0.74 [0.56 to
0.92]°C is therefore larger than the corresponding trend for 1901-2000 given in the TAR of 0.6 [0.4 to
0.8]°C. The linear warming trend over the last 50 years (0.13 [0.10 to 0.16]°C per decade) is nearly twice
that for the last 100 years. The total temperature increase from 1850 – 1899 to 2001 – 2005 is 0.76 [0.57 to
0.95]°C. Urban heat island effects are real but local, and have a negligible influence (less than 0.006°C per
decade over land and zero over the oceans) on these values. {3.2}
• New analyses of balloon-borne and satellite measurements of lower- and mid-tropospheric temperature
show warming rates that are similar to those of the surface temperature record and are consistent within
their respective uncertainties, largely reconciling a discrepancy noted in the TAR. {3.2, 3.4}
• The average atmospheric water vapour content has increased since at least the 1980s over land and ocean as
well as in the upper troposphere. The increase is broadly consistent with the extra water vapour that warmer
air can hold. {3.4}
• Observations since 1961 show that the average temperature of the global ocean has increased to depths of at
least 3000 m and that the ocean has been absorbing more than 80% of the heat added to the climate system.
Such warming causes seawater to expand, contributing to sea level rise (Table SPM-0).{5.2, 5.5}
This is just a summary, if you want download all the
rapport in format PDF (2Mo) > here.global surface temperature9 (since 1850). The updated 100-year linear trend (1906–2005) of 0.74 [0.56 to
0.92]°C is therefore larger than the corresponding trend for 1901-2000 given in the TAR of 0.6 [0.4 to
0.8]°C. The linear warming trend over the last 50 years (0.13 [0.10 to 0.16]°C per decade) is nearly twice
that for the last 100 years. The total temperature increase from 1850 – 1899 to 2001 – 2005 is 0.76 [0.57 to
0.95]°C. Urban heat island effects are real but local, and have a negligible influence (less than 0.006°C per
decade over land and zero over the oceans) on these values. {3.2}
• New analyses of balloon-borne and satellite measurements of lower- and mid-tropospheric temperature
show warming rates that are similar to those of the surface temperature record and are consistent within
their respective uncertainties, largely reconciling a discrepancy noted in the TAR. {3.2, 3.4}
• The average atmospheric water vapour content has increased since at least the 1980s over land and ocean as
well as in the upper troposphere. The increase is broadly consistent with the extra water vapour that warmer
air can hold. {3.4}
• Observations since 1961 show that the average temperature of the global ocean has increased to depths of at
least 3000 m and that the ocean has been absorbing more than 80% of the heat added to the climate system.
Such warming causes seawater to expand, contributing to sea level rise (Table SPM-0).{5.2, 5.5}
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