Transcript Key notes of IPCC Report

• IPCC
---- Intergovernmental Panel On
Climate Change
Recognizing the problem of potential global climate change, the World
Meteorological Organization (WMO) and the United Nations Environment
Program (UNEP) established the Intergovernmental Panel on Climate
Change (IPCC) in 1988. It is open to all members of the UN and WMO.
The role of the IPCC is to assess on a comprehensive, objective, open and
transparent basis the scientific, technical and socio-economic information
relevant to understanding the scientific basis of risk of human-induced
climate change, its potential impacts and options for adaptation and
mitigation.
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IPCC:
first assessment report in 1990
second assessment report in 1995
third assessment report in 2001
fourth assessment report in 2007
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IPCC reports should be the most authoritative reports
on climate change, and are widely cited in almost
any debate related to climate change. The reports
have been influential in forming national and
international responses to climate change.
A small but vocal minority (less than 1.5%) of the
scientists involved with the report have accused the
IPCC of bias.
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Figure SPM.1
Atmospheric concentrations of carbon dioxide, methane and nitrous oxide over the last
10,000 years (large panels) and since 1750 (inset panels). Measurements are shown from
ice cores (symbols with different colours for different studies) and atmospheric samples
(red lines). The corresponding radiative forcings are shown on the right hand axes of the
large panels. {Figure 6.4}
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• Global atmos. 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.
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.
- IPCC report.
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Figure SPM.2
LOSU: assessed level of scientific
understanding
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• The understanding of anthropogenic warming
and cooling influences on climate has improved
since the TAR, leading to very high confidence
that the global average net effect of human
activities since 1750 has been one of warming.
--- IPCC report.
Very high: at least 90% correct
High: at least 80% correct
TAR: Third assessment report (2001).
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Figure SPM.3
Observed changes in (a) global average surface temperature, (b) global average sea
level from tide gauge (blue) and satellite (red) data and (c) Northern Hemisphere
snow cover for March-April. All changes are relative to corresponding averages for the
period 1961–1990. Smoothed curves represent decadal average values while circles
show yearly values. The shaded areas are the uncertainty intervals estimated from a
comprehensive analysis of known uncertainties (a and b) and from the time series (c).
{FAQ 3.1, Figure 1, Figure 4.2, Figure 5.13}
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• 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 average sea level.
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• At continental, regional and ocean basin
scales, numerous long-term changes in
climate have been observed. These include
changes in arctic temperature and ice,
widespread changes in precipitation
amounts, ocean salinity, wind patterns and
aspects of extreme weather including
droughts heavy precipitation, heat waves
and the intensity of tropical cyclones.
--- IPCC report
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TAR: likely; FAR: very likely
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Figure SPM.4
Comparison of observed continental- and global-scale changes in surface temperature with
results simulated by climate models using natural and anthropogenic forcings. Decadal
averages of observations are shown for the period 1906 to 2005 (black line) plotted against
the centre of the decade and relative to the corresponding average for 1901–1950. Lines are
dashed where spatial coverage is less than 50%. Blue shaded bands show the 5–95% range
for 19 simulations from five climate models using only the natural forcings due to solar
activity and volcanoes. Red shaded bands show the 5–95% range for 58 simulations from
14 climate models using both natural and anthropogenic forcings. {FAQ 9.2, Figure 1}
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• Projections of future climate
change
GCMs use a transient climate simulation
to project/predict future temperature changes
under various scenarios. These can be
idealized scenarios (most commonly, CO2
increasing at 1%/y).
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• equilibrium climate simulation
greenhouse gas concentrations are
suddenly changed (typically from preindustrial values to twice pre-industrial
values) and the model allowed to come into
equilibrium with the new forcing.
• transient climate simulation
a mode of running a global climate model in
which a period of time (typically 1850-2100)
is simulated with continuously-varying
concentrations of greenhouse gases so
that the climate of the model represents a
realistic mode of possible change in the
real world.
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The 21st century predicted by the HadCM3 climate model (one of those used by the IPCC)
if a business-as-usual scenario is assumed for economic growth and greenhouse gas
emissions. The average warming predicted by
this model is 3.0°C.
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•
Time evolution of
globally averaged
temperature
change relative to
the period 19611990. The top
graph shows the
results of
greenhouse gas
forcing, the
bottom graph
shows the results
of greenhouse gas
forcing plus
aerosol forcing.
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•
Time evolution of
globally averaged
precipitation
change relative to
the period 19611990. The top
graph shows the
results of
greenhouse gas
forcing, the
bottom graph
shows the results
of greenhouse gas
forcing plus
aerosol forcing.
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SRES: the IPCC special report on Emission
scenarios
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Uncertainties in climate prediction
• (1) Climate models are still failing to take into account all the detailed aspects
of clouds.
Clouds: composed of water vapor => greenhouse gas => incr. T
block sunlight => decr. T
There is no clear consensus on the exact way climate change will modify
these two antagonist effects in the future, because clouds are not explicitely
taken into account in present climate models.
(2) The future climate (say 2100) not only depends on the amount of greenhouse gases
that we already have put in the atmosphere, but also, and mainly, of the amount
we are about to put from now on until 2100.
That's why scientists use emission scenarios, that each describes
how greenhouse gases emissions could evolve between 2000 and
2100, depending on various hypothesis.
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A1 Family is based on the following hypothesis
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Rapid economic growth.
A global population that reaches 9
billion in 2050 and then gradually
declines.
The quick spread of new and
efficient technologies.
A convergent world - income and
way of life converge between
regions. Extensive social and
cultural interactions worldwide.
There are subsets to the A1 family
based on their technological
emphasis:
A1FI - An emphasis on fossil-fuels.
A1B - A balanced emphasis on all
energy sources.
A1T - Emphasis on non-fossil energy
sources.
Btoe: billion ton of oil equivalent.
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A2 family
The A2 scenarios are of a more
divided world. The A2 family of
scenarios is characterized by:
A world of independently operating,
self-reliant nations.
Continuously increasing population.
Regionally oriented economic
development.
Slower and more fragmented
technological changes and
improvements to per capita income.
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B1 Family
The B1 scenarios are of a world more
integrated, and more ecologically friendly.
The B1 scenarios are characterized by:
Rapid economic growth as in A1, but with
rapid changes towards a service and
information economy.
Population rising to 9 billion in 2050 and then
declining as in A1.
Reductions in material intensity and the
introduction of clean and resource efficient
technologies.
An emphasis on global solutions to economic,
social and environmental stability.
Btoe: billion ton of oil equivalent.
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B2 Family
The B2 scenarios are of a world more divided,
but more ecologically friendly. The B2
scenarios are characterized by:
Continuously increasing population, but at a
slower rate than in A2.
Emphasis on local rather than global
solutions to economic, social and
environmental stability.
Intermediate levels of economic development.
Less rapid and more fragmented
technological change than in B1 and A1.
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•
Between the most "optimistic" and the most
"pessimistic" of these scenarios, there is :
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a factor 5 regarding CO2 emissions in 2100,
which reflects the wide range of hypothesis made
on demography, material consumption (that
determines energy consumption, except for
energy efficiency), the energy mix (that is the
proportion of each source in the total), etc
• a factor 2 regarding methane emissions in 2100
(not shown), and a 50% difference regarding the
N2O emissions in 2100 (not shown either).
• a factor 3 regarding SO2 emissions in 2100. SO2
is a good marker of local (or "classical") industrial
pollution, and is an aerosol precursor, or a
"climate cooler".
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Figure SPM.5
Solid lines are multi-model global averages of surface warming (relative to 1980–1999) for the
scenarios A2, A1B and B1, shown as continuations of the 20th century simulations. Shading denotes
the ±1 standard deviation range of individual model annual averages. The orange line is for the
experiment where concentrations were held constant at year 2000 values. The grey bars at right
indicate the best estimate (solid line within each bar) and the likely range assessed for the six SRES
marker scenarios. The assessment of the best estimate and likely ranges in the grey bars includes
the AOGCMs in the left part of the figure, as well as results from a hierarchy of independent models
and observational constraints. {Figures 10.4 and 10.29}
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Figure SPM.6
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Figure SPM.7
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• Monsoon: precipitation (Ch. 10 – IPCC)
Figure 10.9
Multi-model mean changes in surface air temperature (°C, left), precipitation (mm
day–1, middle) and sea level pressure (hPa, right) for boreal winter (DJF, top) and
summer (JJA, bottom). Changes are given for the SRES A1B scenario, for the period
2080 to 2099 relative to 1980 to 1999. Stippling denotes areas where the magnitude of
the multi-model ensemble mean exceeds the inter-model standard deviation. Results
for individual models can be seen in the Supplementary Material for this chapter.
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Figure 10.8
Multi-model mean of annual mean surface warming (surface air temperature
change, °C) for the scenarios B1 (top), A1B (middle) and A2 (bottom), and three
time periods, 2011 to 2030 (left), 2046 to 2065 (middle) and 2080 to 2099 (right).
Stippling is omitted for clarity (see text). Anomalies are relative to the average
of the period 1980 to 1999. Results for individual models can be seen in the
Supplementary Material for this chapter.
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• A global warming will be more rapid over land
than over the oceans, the continental –scale
land-sea thermal contrast will become larger in
summer and smaller in winter => a simple idea
is that the summer monsoon will be stronger
and the winter monsoon will be weaker in the
future than the present.
•
However 15 models results show a weakening
of Hadley cell, Walker cell and monsoon
circulation by 9%, 8% and 14%, respectively, by
the late 21st century. This is because that
pronounced warming over the tropics results in
a reduction in the meridional thermal gradients
between the Asian continent and adjacent
oceans.
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Mean Tropical Pacific Climate Change
• Greenhouse gas => SST increase but not
spatially uniform due to a general reduction
in tropical circulations in a warm climate.
Actually SST increase more over the eastern
tropical Pacific than over the western
tropical Pacific => decrease SLP gradient
along the equator and an eastward shift of
the tropical Pacific rainfall distribution.
 an En Nino-like mean state.
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El Nino
Figure 10.16
The change in El Niño variability (vertical axis) is
denoted by the ratio of the standard deviation of the
first EOF of sea level pressure (SLP) between the
current climate and in the future,
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El Nino (Ch. 10 – IPCC)
• Changes in ENSO interannual
variability differ from model to model.
There is no statistically significant
changes in the amplitude or frequency
of ENSO variability in the future.
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Thermohaline Circulation (Meridional
Overturning circulation (MOC).)
• The increase in greenhouse gases in the
atmosphere leads to decrease of the density
of the surface waters in the North Atlantic
due to warming or a reduction in salinity, the
strength of the MOC is decreased.
• There is still a large spread among the
models simulated reduction in the MOC,
ranging from no response to a reduction of
over 50% by the end of the 21st century.
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If Emissions of Greenhouse gases are reduced, how
quickly do their concentration in the atmosphere
decrease?
Simulated changes in atm. CO2 concen. relative to
the present-day for emission stabilized at the current
level (black), or at 10% (red); 30% (green)… lower
than the present level.
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• Accuracy of models that predict global
warming:
(1) albedo errors
(2) external factors not taken into
consideration
(3) model resolution
(4) initial conditions
(5) the role of clouds on climate
changes
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•
Evidence of some uncertainties:
(1) The individual models often exhibit worse agreement
with observations.
(2) All models have shortcomings in their simulations of the
present day climate of the stratosphere, which might limit
the accuracy of predictions of future climate change.
(3) There are problems in simulating natural seasonal
variability.
(4) Coupled climate models do not simulate with reasonable
accuracy clouds and some related hydrological processes.
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•
Evidence of model reliability:
(1) The model mean exhibits good
agreement with observations.
(2) Surface air temperature is particularly
well simulated.
(3) For nearly all models the r.m.s. error
in zonal- and annual-mean surface air
temperature is small compared with its
natural variability.
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Conclusion
=============
The majority of climatologists agree that
important climate processes are
imperfectly accounted for by the climate
models but don't think that better
models would change the conclusion.
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