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Climate change: human-induced effects and natural fluctuations
Climate Change
Human-induced effects and/or
natural fluctuations?
Alberto Montanari - University of Bologna - [email protected]
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
Why to study climate change is important??
• Water resources management – Water Framework Directive
- Evaluation of future water resources availability
- Design of measures for contrasting water scarcity (water
management policies, artificial reservoirs).
- Implementation of economical policies.
• Design of water distribution networks
- Evaluation of future water demands.
• Assessment of hydrological risk
- Assessment of future flood flows.
- Design of river engineering works.
- Design of civil protection measures.
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
Climate change is a controversial issue…..
Despite of what the media tell us, detection of climate change is
subject to a relevant uncertainty.
Climate is surely changing, but….
Scientific questions (often not mentioned by
the media):
- Is the climate change irreversible or is it
just a temporary fluctuation?
- If it is a temporary fluctuation, how long is
it?
- Climate change is a human-induced effect
or a natural variation?
These scientific questions have relevant
economic and social implications – Much
more relevant than what we can imagine!
Remember: climate is changing for sure!
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
A practical example - 1
Water resources management – Water Framework Directive
- In order to meet the demands of the Water Framework Directive, regional
administrations in Italy have to prepare a master plan for water management.
- In the Emilia-Romagna region, the master plan has to propose efficient
solutions for mitigating the impacts due to the release of the environmental
flow.
- Water resources managers are undergoing a political pressure in order to
substantiate the necessity of a huge dam on a Appennine River, that should
accumulate water during the winter to assure water for irrigation and
environmental flow during the summer.
- Politicians say that the dam is needed because we cannot withdraw water
from the Po River anymore, because climate change is reducing the Po river
flows. However….
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
A practical example - 2
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Climate change: human-induced effects and natural fluctuations
A practical example - 3
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Climate change: human-induced effects and natural fluctuations
A practical example - 4
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Climate change: human-induced effects and natural fluctuations
A first scientific example – Global warming due to greenhouse effects
The “Official” Warming Estimates
(U.N. Intergovernmental Panel on Climate Change)
Computerized climate models have led to future warming
estimates by 2100 of from 1.1 to 2.9 deg. C (low emissions) to
2.4 to 6.4 deg. C (high emissions)..
Direct surface warming from 2xCO2 is only 0.6 deg C
(about 1 deg. F)
Thus, climate models have net POSITIVE feedbacks (they
respond to a warming tendency with changes that amplify the 1
deg. F CO2-only warming).
There is a WIDE range of warming estimates, illustrating
substantial uncertainty (mainly from cloud feedback differences
between models)
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
Why warming estimates could be overly pessimistic.
 The Earth’s greenhouse effect is mostly due to water vapor
and clouds, which are under the control of weather processes
(mostly precipitation systems).
 A few percent increase in low clouds, or a small increase in
precipitation efficiency, could entirely offset the warming
tendency from carbon dioxide (neither of these processes are
well understood).
 Big Question: Do precipitation systems stabilize the Earth’s
temperature at a preferred temperature?
Alberto Montanari, University of Bologna, [email protected]
Most of our atmosphere is being continuously
Climate
change:
effects and
natural
recycled
byhuman-induced
precipitation systems,
which
then fluctuations
determine the strength of the Greenhouse Effect
Cooling (loss of IR radiation)
by dry air to space
Heat
released through
condensation
causes air to rise,
rain falls to surface
Air sinks in
response to precipitation systems:
Sinking air is relatively dry
Boundary layer
warm, humid air
evaporation
removes heat
Alberto Montanari, University of Bologna, [email protected]
Sunlight absorbed
at surface
cool, dry air
Ocean or Land
Climate change: human-induced effects and natural fluctuations
Climate Models do not yet
contain the processes that stabilize the climate
system against significant warming.
MOST of these stabilizing processes can probably be traced to
“thermostatic” effects of precipitation systems, which
adjust global water vapor and cloud amounts to maintain a natural
Greenhouse Effect and temperatures that depend
upon how much sunlight is available.
Bottom Line: How much you believe climate model predictions
of future warming depends upon how much faith you have that
the models contain all of the important atmospheric processes
(feedbacks) that determine how the atmosphere responds to
greenhouse gas forcing.
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
A second scientific example - The Hockey stick controversy
http://en.wikipedia.org/wiki/Hockey_stick_controversy
Mann et al. 1998.
McIntyre and McKitrick, 2005;
See http://www.realclimate.org
and http://www.climateaudit.org.
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
A second scientific example - The Hockey stick controversy
Manipulation operated by the Media
(Uncertain results given as certain…..)
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
A second scientific example - The Hockey stick controversy
Manipulation operated by the Media
(Presentation of partial results…..)
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
The famous Mann et al. “Hockey Stick” had errors in
statistical analysis methods.
(A National Academies Review Panel [July 2006]
changed the Hockey Stick conclusion from
“warmest in 1,000 years” to “warmest in 400 years”)
McIntyre-McKitrick, 2003
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
We are probably not
as warm as during
Medieval Warm Period
The GRIP (Greenland) borehole record is one of the best records because it is not a proxy, it is a DIRECT measure
of temperature. Shown are the last 2000 years. (Dahl-Jensen et al. 1998, Science, 282, 268-271 "Past Temperatures
Directly the Greenland Ice Sheet"). A similar reconstruction occurs for the Ural Mountain borehole temperatures
Alberto Montanari, University of Bologna, [email protected]
(i.e. warmer 1000 years ago, Bemeshko, D., V.A. Schapov, Global and Planetary Change, 2001.
Climate change: human-induced effects and natural fluctuations
Climate change
Manipulation operated by the Media
(Catastrophic views…..)
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
Climate change
Manipulation operated by the Media
(Catastrophic views…..)
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
Climate change
Is it possible to gain an impartial view???
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
A fundamental starting point: the IPCC fourth assessment report
The Intergovernmental Panel on Climate Change (IPCC) has been established by World
Meteorological Organisation (WMO) and UNEP (United Nations Environment
Programme) to assess scientific, technical and socio- economic information relevant for
the understanding of climate change, its potential impacts and options for adaptation and
mitigation. It is currently finalizing its Fourth Assessment Report "Climate Change
2007", also referred to as AR4. The reports by the three Working Groups provide a
comprehensive and up-to-date assessment of the current state of knowledge on climate
change.
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
IPCC fourth assessment report
http://www.ipcc.ch/SPM13apr07.pdf
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
The IPCC fourth assessment report
Independent Summary for Policy Makers
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
The IPCC fourth assessment report
Independent Summary for Policy Makers
The growth rate of CO2 emissions (in carbon equivalent) is equal to or slightly below
the growth rate of world population (see Figure ISPM-2). Global per capita carbon
emissions peaked at 1.23 tonnes per person in 1979 and the per-person average has
declined slightly since then.
As of 2003 the global average is 1.14 tonnes per capita, an average that has not
changed since the early 1980s. If this trend continues, global emissions growth in the
future will be constrained by total population growth.
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
The IPCC fourth assessment report
Independent Summary for Policy Makers - Sun
If the sun does have a strong effect on climate, this adds importance to
recent projections that solar output is likely to decline over the next several
decades (e.g., Zhen-Shan, 2007)
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
The IPCC fourth assessment report
Independent Summary for Policy Makers - Temperature
Problems with the surface temperature record
Research on the nature of the surface thermometer network has cast
some doubt on the claim of the IPCC that the surface temperature
record is free of biases related to non-climatic effects, such as land-use
change, urbanization and changes in the number of stations worldwide.
For example, studies have shown that the spatial pattern of warming
trends over land correlate strongly with the distribution of industrial
activity, even though such a correlation is not predicted by climate
models (e.g., de Laat and Maurellis 2004, 2006).
Urban heat island effect
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
The IPCC fourth
assessment report
Independent Summary
for Policy Makers
Temperature
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
The IPCC fourth assessment report
Independent Summary for Policy Makers - Precipitation
• There is no globally-consistent pattern in long-term precipitation
trends.
• At the global level, slight decline was observed in total precipitation
from 1950 to the early 1990s, which has since reversed.
• Precipitation in North and South America has risen slightly over the
past century in many places, though in some regions it has fallen.
• The drying trend noted in the 1980s in the Sahel (the coastal
region in Africa bordering the Sahara desert) has since reversed
considerably.
• Rainfall in India increased from 1901 to 1979 then declined through
to the present and there is no overall trend. Australian precipitation
trends vary by region and are closely linked to the El Niño cycle.
• Perceptions of increased extreme weather events are potentially
due to increased reporting. There is too little data to reliably
confirm these perceptions.
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
The IPCC fourth assessment report
Independent Summary for Policy Makers – Sea level
• Regional trends in sea level are quite varied and some regions are
experiencing declining sea levels. Changes in air pressure and wind account
for some observed sea level increase.
• While global sea level rose by approximately 120 metres during the several
millennia that followed the end of the last glacial maximum, the level stabilized
between 3000 and 2000 years ago. Since then, paleo sea level indicators
suggest that global sea level did not change significantly: the average rate of
change from 2000 years ago to about 100 years ago is near zero.
• Although regional variability in coastal sea level change had been reported
from tide gauge analyses, the global coverage of satellite altimetry provides
unambiguous evidence of non-uniform sea level change in open oceans.
• For the past decade, the western Pacific Ocean and eastern Indian Oceans
show the highest magnitude of sea level rise, however, sea level has been
dropping in the eastern Pacific and western Indian Oceans.
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
The IPCC fourth assessment report
Independent Summary for Policy Makers – Sea level
• Except for the Gulf Stream region, most of the Atlantic Ocean shows sea level rise
during the past decade.
• Sea level increases over the past decade are not uniform, and it is presently
unclear whether they are attributable to natural variability.
• The instrumentally-based estimates of modern sea level change provide evidence
for an onset of acceleration at the end of the 19th century. Recent estimates for
the last half of the 20th century (1950.2000) give approximately 2 mm/year global
mean sea level rise.
• New satellite observations show that since 1993 sea level has been rising at a rate
of 3.1 mm/year.
• Satellite data also confirm that sea level is not rising uniformly over the world.
• It is presently unclear whether the higher rate of sea level rise in the 1990.s
indicates an acceleration due to global warming, or a result of natural climate
variability, or a combination of both effects.
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
The IPCC fourth assessment report
Independent Summary for Policy Makers Snow and Glacier
• Most archives from the Northern Hemisphere and the tropics show small or absent
glaciers between 9,000 and 6,000 years ago.
• Glaciers began growing thereafter, up to the 1800s. This tendency is primarily related
to changes in the Earth’s orbit. However shorter, decadal-scale, regionally diverse
glacier responses must have been driven by other factors which are complex and
poorly understood.
• General retreat of glacier termini started after 1800, with considerable mean retreat
rates in all regions after 1850 lasting throughout the 20th century. A slowdown of
retreats between about 1970 and 1990 is evident in the raw data. Retreats were again
generally rapid in the 1990s; though advances of glaciers have been observed in
western Scandinavia and New Zealand.
• There are few records of directly measured glacier mass balances, and they stretch
back only to the mid 20th century. When areal weighting and spatial interpolation are
used to estimate large-scale patterns from the available data, the 1990s trend towards
glacier retreat appears to have leveled off or reversed after 1998.
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
The IPCC fourth assessment report
Independent Summary for Policy Makers - Paleoclimate
The earth was ice-free during most of its history.
The Pliocene (about 3 million years ago) was the most recent time in Earth’s
history when mean global temperatures were substantially warmer (about 2°C
to 3°C warmer).
On the other hand, temperatures during most of the most recent 1 million years
(the Pleistocene) have been colder than at present. Long glacial periods have
alternated with short (10 to 30,000 year long) interglacials.
Globally, there was less glacial ice and higher sea level on Earth during the
Last Interglacial than now. This suggests significant meltback of the Greenland
and possibly Antarctica ice sheets occurred. The climate of the LIG has been
inferred to be warmer than present, although the evidence is regional and not
neccessarily synchronous globally.
The causes of large-scale climate variations on the century and longer time
scales are not well-understood.
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
The IPCC fourth assessment report
Independent Summary for Policy Makers – Climate models
The output and the projections of climate models are highly uncertain.
Climate models are calibrated.
Some observational data do not concur with the output of climate models.
Different models provide different outcomes with a wide spread.
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
The IPCC fourth assessment report
Independent Summary for Policy Makers – The attribution problem
The climate is subject to natural variability over a wide range of time scales
Internal variability and irreversible change are difficult to distinguish (if not
impossible, given the present state of the knowledge).
The current level of uncertainty in climate studies prevents to reach statistically
significant conclusions.
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
The IPCC fourth assessment report
Independent Summary for Policy Makers – Conclusions
The climate in most places has undergone minor changes over the past
200 years, and the land-based surface temperature record of the past
100 years exhibits warming trends in many places. Measurement
problems, including uneven sampling, missing data and local land-use
changes, make interpretation of these trends difficult. Other, more stable
data sets, such as satellite, radiosonde and ocean temperatures yield
smaller warming trends. The actual climate change in many locations has
been relatively small and within the range of known natural variability.
There is no compelling evidence that dangerous or unprecedented
changes are underway.
Alberto Montanari, University of Bologna, [email protected]
Climate change: human-induced effects and natural fluctuations
Alberto Montanari, University of Bologna, [email protected]