Download IntellBldgPart1_2009fin - University of Reading, Department of

Climate Change
and
Urban Climate
Dr Janet Barlow
Department of Meteorology, University of
Reading
[email protected]
MSc Intelligent Buildings
March 2009
1
Structure of today’s session
Part 1: Climate Change
(the global picture)
Key reference:
Intergovernmental Panel on Climate Change
IPCC
4th Assessment Report
http://www.ipcc.ch/index.htm
Part 2: Urban Climate
(climate at the scale of buildings)
2
Part 1: Climate change
• What is climate?
• Has climate changed in the recent past?
• What might have caused climate to
change?
• What might happen in the future?
• What can we do about it?
3
What is climate?
“Climate is what we expect, weather is
what we actually get” Ed Lorenz
A full description of climate includes:
global means, geographical, seasonal
and day-to-day variations of
temperature, precipitation, radiation,
clouds, snow cover etc.
4
Temperature changes 1
Global mean temperature
has increased by
0.6±0.2 C since 1900
For b) satellite data shown in
red, tide gauge in blue
For c), snow is Mar/Apr cover
All changes shown with respect
to 1961-1990 average.
Smoothed curves decadal
values, dots are yearly values.
Shaded area are uncertainty
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intervals.
Although it’s really about global change… some places have
seen very large warming, other regions have actually cooled.
Linear trends in annual
temperature (degC per century)
Grey areas – insufficient data
Trends significant at 5% level
indicated by + marks.
…although in recent years,
warming predominates
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The evidence for global warming
is mounting!
INCREASE
•
•
•
•
Length of freeze free season
Length of growing season
More frequent heat waves
Wetter winters/Drier
summers
• Sea level rise (0.1-0.2m
during 20th century, mostly
due to thermal expansion of
ocean)
DECREASE
• Extent of mountain
glaciers
• Sea-ice amounts and
thickness (NH
decreased by 10-15%
since 1950s)
• Snow cover (10%
reduction in NH snow
cover since 1960s)
• Fewer Frosts
7
Climate change is not unprecedented
The earth has
been capable of
rapid transitions in
the past…
8
However, the northern hemisphere is probably
the warmest it’s been for at least 1000 years…
Reconstruction using proxy records
like tree rings and ice cores
Mann et al., Science 1999 (Northern Hemisphere
9
only)
… the rise in temperature is strongly
correlated with a rise in the emission of
certain gases into the atmosphere by
human activities….
10
Concentrations are now higher than for the past
several thousand years…
Ice core data – different colours
indicate different studies.
Atmospheric measurements –
red lines
11
IPCC (2001)
… And the present
trends in CO2 and
methane are
outside those
experienced on
earth for at least
the last 400,000
years…..
12
What might have caused
these changes?
• The balance of evidence suggests that there is a
discernible human influence on global climate (IPCC,
1995)
• There is new and stronger evidence that most of the
warming over the past 50 years is attributable to
human activities (IPCC 2001)
• Most of the observed increase in global average
temperatures since the mid-20th century is very likely
due to the observed increase in anthropogenic
greenhouse gas concentrations (IPCC 2007)
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Fundamental processes – many interacting
components
14
For a stable climate, the earth must be in energy balance
IPCC
2001
Energy absorbed
Energy radiated
by surface and = from Earthatmosphere
Atmosphere and
ocean to space
30% of incoming
radiation is
reflected back to
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space
The “natural greenhouse effect”
Release of carbon dioxide and other gases from human activities enhances
the greenhouse effect and causes the Earth to absorb around 2Wm-2 more
radiation than it emits  global warming
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Natural climate forcing
mechanisms
• Solar variability
• Volcanic eruptions
17
Solar
variability: 1
• Changes in the Sun’s strength
– 11 year cycle with sunspots
– small changes that have little impact compared to
greenhouse gas changes
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Solar variability: 2
• Changes in Sun-Earth geometry
– Sun-Earth distance, tilt of Earth and ellipse
of orbit
– act over very long timescales, many
thousands of years
– possibly play a role in inducing ice ages but
not important on past 250 years time scale
– at current time provides a cooling influence
on climate
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Volcanoes
Large eruptions like Pinatubo
(1991) put clouds of sulphur
dioxide gas into stratosphere,
above the weather.

cloud of sulphuric acid droplets
scatter and absorb solar radiation

cooling of surface and warming of
stratosphere
But, aerosols only last a few years, so generally climate
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impact only lasts a few years
Observed effect on T
IPCC
2001
El Chichon
Pinatubo
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Anthropogenic causes
• Greenhouse gases
• Ozone changes (stratospheric and
tropospheric)
• Tropospheric aerosols
• Surface albedo changes
• Heat pollution
22
Greenhouse gases
• Water vapour is most important natural
greenhouse gas, but we don’t usually change it
directly so don’t consider it part of
anthropogenic climate change
• Strength of a greenhouse gas depends on
–
–
–
–
strength of absorption of infra-red radiation
overlap of absorption with other gases
lifetime in the atmosphere
amount added over given period of time
CO2 (carbon dioxide), CH4 (methane), N2O (nitrous
oxide), CFCs/HCFCs/HFCs
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Strengths of greenhouse gases
Gas
CO2
CH4
N2O
HFC-23
HFC-32
HFC-41
HFC-125
HFC-134a
SF6
CF4
C2F6
C3F8
Lifetime
(years)
Variable
12.2
120
264
5.6
3.7
32.6
14.6
3200
50000
10000
2600
Forcing per
ppbv (Wm-2)
1.8x10-5
3.7 x 10-4
3.7 x 10-3
0.18
0.11
0.02
0.20
0.17
0.64
0.10
0.23
0.24
Forcing so far
(Wm-2)
1.56
0.46
0.14
0.002
0.007
GWP rel. to
CO2 (100 yrs)
1
21
310
11700
650
150
1300
1300
239000
6500
9200
7000
GWP rel. to
CO2 (500 yrs)
1
6.5
170
9800
200
45
920
420
34900
10000
14000
10100
“Forcing”: measure of perturbation to energy budget
“GWP”: Global warming potential (combines forcing with
lifetime of gas)
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Ozone
• Spatially nonuniform
• Radiative forcing
depends critically
on level at which
ozone changes:
–troposphere: ozone has increased and produces a
positive radiative forcing (a pollutant at this level)
–stratosphere: ozone has decreased implying less
absorption and re-emission of IR radiation
producing a negative forcing (also small +ve forcing
due to increased solar radiation reaching the
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surface)
Tropospheric aerosols
• Tiny particles (or droplets)
• Many different types from both natural
and anthropogenic sources:
– dust (from land-use change)
– sulphates (fossil fuel burning)
– soot (fossil fuel and biomass burning)
– organic droplets (fossil fuel and biomass
burning)
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Aerosols: Direct solar effect
• Aerosols scatter and absorb solar
radiation
No aerosol
Scattering
aerosol
Absorbing
aerosol
Negative
radiative forcing
 cooling
Positive radiative
forcing  warming
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CO2 vs aerosol forcing
•Cannot be used to
cancel out
greenhouse gas
forcing (patterns are
completely different)
•Response may also
be different
•Indirect effect is
Sulphatesvery uncertain but
potentially large
CO2
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Other anthropogenic effects
• Land use changes alter the albedo and
the amount of solar radiation reflected
back to space.
• Urban and industrial regions output
large amounts of local heat.
• Important regionally and may modify
the circulation
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Relative roles: IPCC 2007
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The future: Human influences will continue to
change atmospheric composition throughout
the 21st century
How quickly the climate will change in the future
depends on:
• How much greenhouse gas emissions grow
–depends on population growth, energy use, new
technologies, etc
• How sensitive the climate system is to emissions
– how clouds, ice, oceans etc respond to the extra heating
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Uncertainty
• Being uncertain does not mean that we know
nothing!
• Many simplifications and assumptions must
be made to make useable models of the
climate system
• There are often different ways of doing this
and sometimes there isn’t a “best” method.
• This variation leads to differences in the
feedbacks in models and differences in the
future predictions
32
How good are climate models?
FAR – 1st assessment report
(1990)
SAR – 2nd (1996)
TAR – 3rd (2001)
Shaded areas indicate range of
model predictions
Dots show annual mean
variations
Black line is decadal variations
obtained by smoothing data
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Models recreate C20th warming only WITH anthropogenic influence
Temperature
anomalies with
respect to 19011950 average
Dashed black line
– less than 50%
spatial data cover
Shaded areas
indicate 5-95%
range over many
simulations from
different climate
models
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The Future: you ain’t seen nothing yet…
Temperature
anomalies with
respect to 19801999 average
Shaded colour areas
indicate ±1 standard
deviation; grey bars
indicate range of
predictions
Emission scenarios:
A1B: rapid economic
growth, mix of
energy sources
A2: Fragmented
regional economic
growth
B1: clean
technology, 35
global
solutions
Land areas are projected to warm more than the oceans with the
greatest warming at high latitudes
Temperature anomalies with respect to 1980-1999 average
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2100: A Different Climate!
• Increase in global mean temperature of 1.4°C 5.8°C.
• Sea level rise by a further 0.09m – 0.88m.
• Change in frequency and duration of extreme
weather events.
• Increase in the number of hot days, and decrease in
number of cold days.
• Increase in precipitation over northern hemisphere.
BUT there are SERIOUS impacts too…
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Future impacts
38
Impacts of change in water runoff
Percentage change of 2081-2100 with respect to 1981-2000 average
A1B (“Rapid”) scenario
39
2050: Millions displaced by sea-level rise
>1million
50,000 to 1 million
5,000 to 50,000
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So what can we do about it?
• Mitigation? (Working Group 3 IPCC)
(Energy efficiency, “clean” energy and
technology transfer to developing countries)
• Adaptation? (Working Group 2 IPCC)
(Some will be necessary as we are already
committed to some change)
42
Kyoto Protocol
• Reduction of emissions of CO2,
CH4, N2O and “basket of 6
gases” which includes SF6 and
several of the HFCs
• Ratification (particularly by
US)?
• Role of developing nations?
http://unfccc.int/kyoto_protocol/items/2
830.php
http://en.wikipedia.org/wiki/Kyoto_Proto
col
11th December 1997, Japan – adopted
16th February 2005 – enforced
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Contraction and convergence: an equitable solution?
FSU: Former Soviet Union. See Global Commons Institute www.gci.org.uk
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Even if we act quickly….the climate
responds slowly
10s/100s yrs
~ 100 years
Stabilised
Stabilised
emissions
CO2 concs
in the
atmosphere
Stabilised
surface
temperature
100s / 1000
yrs
Stabilised
sea level
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What have we found so far?
• Climate change is unlikely to be solely the
result of either natural or anthropogenic
effects
• Complexity is still an issue, especially
interaction of biosphere and other
components
• Model predictions quite good for global
temperatures – but regional predictions still
uncertain
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Websites on Climate Change
• Intergovernmental Panel on Climate Change
http://www.ipcc.ch/index.htm
• DEFRA website on climate change:
http://www.defra.gov.uk/environment/climatechange/
• UK Climate Impacts Programme:
http://www.ukcip.org.uk/
• climateprediction.net – take part in online climate
change experiment:
http://www.climateprediction.net/index.php
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