Transcript cchange - University of Reading

Climate change and pollution
Eleanor J Highwood
Department of Meteorology,
University of Reading
MSc Intelligent Buildings April 2002
Outline: climate change
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What is climate?
Has climate changed in the recent past?
If so has any change been unusual?
What might have caused climate to change?
Can we model climate change?
What might happen in the future?
What is there left to do?
What is climate?
“Climate is what we expect, weather is what
we actually get”
A full description of climate includes:
global means, geographical, seasonal and
day-to-day variations of
temperature, precipitation, radiation, clouds,
snow cover etc.
Has climate changed in the recent
past?
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•
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•
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Temperature changes
Sea level rise
Precipitation changes
Mountain glaciers
Snow cover
Temperature changes 1
Global mean T of air at Earth’s surface has 
by 0.6 +/- 0.2 C over the 20th century.
IPCC
2001
Temperature changes: 2
• Regional changes can be much larger than
global means; some places have also
cooled: “global warming” is a misnomer.
• Size of warming depends on time period
considered and time of year considered.
Variation of warming with time period IPCC 2001
Seasonal variation in warming IPCC 2001
Temperature changes: 3
• Over the period 1950 to 1993, diurnal
temperature range has reduced because the
nights have warmed more than the days.
Sea level changes
• Observed rise
of 0.1 - 0.2m
during 20th
century. Rises
are of order
2mm/year
• Mostly due to
thermal
expansion of
oceans
Precipitation changes
•  over land in
tropics and midlatitudes and  in
the subtropics.
• NH mid-latitudes
have seen an
increase of 2-4% in
frequency of heavy
precipitation events
Mountain
glaciers
• Shrinkage of
many glaciers
since 1890. If it
reaches the
oceans this
contributes to
sea-level rise.
Snow cover
• 10% reduction in
NH snow cover
between 1960s and
present day
Sea ice
• NH sea ice
extent has
decreased by
10-15% since
1950s
Have changes been unusual?
Proxy records:
–
–
–
–
tree rings (past 100 years)
shallow ice cores
corals
deep sea sediments (past 10, 000 years)
Natural variability: changes resulting from
interactions between components of climate
system
Changes over past 1000 years (from Mann et al 1999
Natural
variability:1
There have been large
changes in
temperature in the past
Natural variability:2
Even a climate with no forcing has a lot of
variability (IPCC 2001)
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)
Fundamental processes
• Many interacting components
Energy balance
Solar energy absorbed by
the Earth-atmosphere
system
=
Energy radiated from
Earth- Atmosphere
system to space
S0 (1- p) re2 = 4 re2  Te4
30% of incoming solar radiation reflected to space by clouds,
surface, molecules and particles in the atmosphere (albedo).
Radiation and climate
IPCC 2001
The “natural greenhouse effect”
Ta4
Ts4
Ta4
Earth radiates to space
Atmosphere absorbs radiation from
ground and re-emits less radiation
since it is colder (=0.77)
Atmosphere traps radiation and warms surface so that life can
exist.
Radiative forcing, F
• Radiative forcing measures the change to
the energy budget of the atmosphere.
Positive  surface T 
Negative  surface T 
• Easier to calculate than change in
temperature, but related to temperature
change by T= F where  is the climate
sensitivity.
Radiative forcing due to  in
solar output
ASR = OLR
System in
balance
ASR > OLR
OLR must increase
to balance ASR, so
system must warm
up. F +ve
Radiative forcing due to  in
carbon dioxide
ASR = OLR
System in
balance
OLR < ASR
CO2 raises  so more
radiation comes from
cold atmosphere so OLR
increases
OLR must increase
again to balance
ASR, so system
must warm up. F
+ve
Possible causes of climate change
Natural climate change
• Solar variability
• Volcanic eruptions
Solar variability: 1
• Changes in
the Suns
strength
– 11 year
cycle with
sunspots
– small
changes
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
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 impact
only lasts a few years (apart from cumulative effect? )
Observed effect on T
IPCC
2001
El Chichon
Pinatubo
Anthropogenic causes
• Greenhouse gases
• Ozone changes (stratospheric and
tropospheric)
• Tropospheric aerosols
• Surface albedo changes
• Heat pollution
Greenhouse gases: 1
• Water vapour is most important natural
greenhouse gas, but we don’t usually
change it directly
• 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
Greenhouse gases: 2
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CO2 (carbon dioxide)
CH4 (methane)
N2O (nitrous oxide)
CFCs/HCFCs/HFCs
(chlorofluorocarbons/hydrochlorofluorocarb
ons/hydrofluorocarbons)
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
CO2 :1
Risen by 31%
since 1750,
roughly in line
with emissions
from fossil
fuel burning
CO2 :2
• Rate of recent increase has been
unprecedented
• Also increased by deforestation in the
tropics and biomass burning
• Lifetime of 200 years and is slow to
respond to changes in emissions
Carbon cycle
CH4 :1
• Increased
by 50%
since 1750
and
continues
to increase.
CH4
• Current concentrations have not been
exceeded in 420 thousand years
• From rice-growing, domestic cattle, waste
disposal and fossil fuel burning
• 12 year lifetime (a quick-fix for “global
warming”)
N2O
• Increased by
17%
• Unprecedented
in past 1000
years
• Half of current
emissions are
anthropogenic
(fertilisers etc)
CFCs
CFCs contain chlorine which damages the
ozone layer in the stratosphere. They last 50
years or more and so built up in the
atmosphere during 1970s/80s. Banned
under Montreal Protocol

Replaced temporarily by HCFCs which still
contain chlorine but break down in
atmosphere much more quickly
HFCs
• No chlorine (therefore don’t affect ozone
layer)
HFCs
• No chlorine (therefore don’t affect ozone
layer)
BUT
• they are powerful greenhouse gases and
very long-lived
• Entirely anthropogenic in origin (and used
in a variety of odd ways!)
• Rising quickly in the atmosphere
Emission of CFCs etc
CF4
SF6
Ozone
• Spatially non-uniform
• Radiative forcing depends critically on level
at which ozone changes:
– troposphere: ozone has increased and produces
a positive radiative forcing
– 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 surface)
Tropospheric ozone changes
Tropospheric aerosols
• Tiny particles (or droplets)
• Many different types from both natural and
anthropogenic sources:
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–
–
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dust (from land-use change)
sulphates (fossil fuel burning)
soot (fossil fuel and biomass burning)
organic droplets (fossil fuel and biomass
burning)
Aerosols: Direct solar effect
• Aerosols scatter and absorb solar radiation
No aerosol
Scattering aerosol
Absorbing aerosol
Aerosols: Direct terrestrial effect
• Large aerosols (e.g. dust or sulphuric acid in
the stratosphere) behave like greenhouse
gases.
No aerosol: ground emits to
space
Aerosol absorbs radiation from
ground and re-emits a smaller
amount up and down
Aerosols: Indirect effects
• Some aerosols
can alter the
properties of
clouds, changing
their reflectivity
or lifetime
Aerosol forcing
• Magnitude and sign of forcing depends on
distribution and mixing
• Very spatially non-uniform distributions
Aerosol forcing
• Cannot be used to cancel out greenhouse
gas forcing (patterns are completely
different)
• Response may also be different
• Indirect effect is very uncertain but
potentially large
CO2 vs aerosol forcing
CO2
Sulphates
Land albedo changes
• Land use changes alter the albedo and the
amount of solar radiation reflected back to
space.
Heat pollution
• Urban and industrial regions output large
amounts of local heat.
• Important regionally and may modify the
circulation
Radiative forcing since 1750
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GHG: +2.43 Wm-2 (60% CO2, 20% CH4)
Tropospheric ozone: +0.35 Wm-2
Stratospheric ozone: -0.15 Wm-2
Tropospheric aerosols (direct):
– sulphates (-0.4 Wm-2), biomass (-0.2 Wm-2),
organics (-0.1 Wm-2), black carbon (+0.2 Wm2), dust ?
• Indirect effect: -0 to -2 Wm-2
• Solar: +/- 0.2 Wm-2
Can we model climate change?
At the simplest level we can relate:
T=F
But what is ? Represents feedbacks between
climate components.
Many feedbacks, three very important ones.
Water vapour - temperature
feedback
 T (e.g. due
to CO2)
Water vapour
is a
greenhouse
gas, therefore
+ve feedback
More water
vapour in the
atmosphere
More
evaporation at
the surface
Snow/ice - temperature feedback
 T (e.g. due
to CO2)
More solar
energy is
absorbed at the
surface,
therefore
+ve feedback
Planetary albdeo
increases
Less snow and
ice
Cloud feedback
• Clouds can reflect solar radiation (low thick
clouds) and act as greenhouse gases (high
thin clouds)
• Uncertain as to how clouds changes in a
changing climate or how these changes
would feedback to climate
• positive or negative feedback?
Other feedbacks
• biosphere
Climate modelling
We use climate models to:
– model present day climate and understand
physical processes
– model past climate and attribute change to
particular mechanisms
– predict future climate change
Types of model:1
• There are 2 approaches of model
• “empirical statistical”: based on
extrapolation from previous climates that
have occurred - can’t predict anything new
• “first principles”: based on fundamental
mathematical equations governing fluid
dynamics - can predict new situations
Model validation
• Simulate present day climate
• Individual components such as radiation /
convection
• Simulate past climates of Earth
• Simulate climates of other planets
Hierarchy of models
0 dimensions (e.g. simple
energy balance model)
Latitude - altitude
Latitude - longitude
(chemistry models)
(paleoclimate models)
3-D models
“slab ocean”
Coupled
atmosphere/ocean
models
Types of experiments
“Equilibrium response”
“Transient response”
Perturb the atmosphere
and do a long simulation
until energy balance us
restored at a new
equilibrium, then record
temperature change.
Can be done with a
simplified model.
Perturb the atmosphere
and examine the
temperature as a function
of time - allows us to
examine what happens at
a given time, but needs a
good ocean and is more
more expensive.
Temperature changes
What might happen in the future
“Human influences will continue to change
atmospheric composition throughout the
21st century” (IPCC,2001)
We can have most confidence in those
changes predicted consistently by several
different models.
Future temperature changes
• Increases in global mean temperature of 1.4
- 5.8 C by the year 2100
• Greater warming over land than over ocean,
especially in North America and northern
and central Asia during the cold season
• Probably an increase in number of hot days
and decrease in cold days
• Night-time increase more than day-time
T
Precip.
Future sea level changes
• Rise by a further 0.09 to 0.88m by the year
2100
• Half of this rise comes from thermal
expansion, remainder from melting glaciers
and the Greenland ice sheet
Other future changes:1
• Increases in global averages and variability
of both precipitation and evaporation (NH
mid-lats more rain than snow)
• Increased summer heating decreases soil
moisture
• recent trends for SST patterns to become
more El Nino -like
Other future
changes: 2
• Change in
frequency and
duration of extreme
events
• Possible but very
uncertain changes
in weather events
Impacts
• Increases in heatwaves - increase in
mortality due to heat stress
• flooding
• coastal erosion
• agricultural yields decrease in places
• extension of desertification
• pressure on water resources
• spread of disease and pest to new areas
The number of people at risk by the 2080s by the coastal
regions under the sea-level rise scenario and constant
(1990s) protection, showing the regions where coastal
wetlands are most threatened by sea-level rise.
(From Met Office)
Percentage change in average
crop yields for the climate
change scenario:
wheat, maize and rice.
(From Met Office)
Change in natural
vegetation type
(From Met. Office)
Change in water stress,
due to climate change, in
countries using more than
20% of their potential
water resources
(From Met Office)
Potential transmission
of malaria
a) baseline climate
conditions (19611990)
b) climate change
scenario for the
2050s.
(From Met Office)
Impacts for the UK
Much harder to predict regional climate
change
• Northwards shift of vegetation by 50-80km
per decade
• impacts on wildlife, soils, water resources
and agriculture in South
Legislation
Mitigation vs adaptation?
• To prevent any further rise in CO2 we
would need to cut emissions by 60%
• Can stressed ecosystems adapt fast enough?
• Migration is in many places impossible
Timescale for future change
10s/100s yrs
Stabilised
Stabilised
emissions
CO2 concs
in the
atmosphere
~ 100 years
100s / 1000 yrs
Stabilised
surface
temperature
Any response to changes we make will be very slow.
Stabilised
sea level
Kyoto Protocol
• Reduction of emissions of CO2, CH4, N2O
and “basket of 6 gases” which includes SF6
and several of the HFCs
• Role of carbon sinks uncertain
• Ratification (particularly by US)?
• Role of developing nations?
Measures for Kyoto Protocol
• Global Warming Potentials (accounts for
strength and lifetime of greenhouse gases)
• Total Equivalent Warming Impact (TEWI)
e.g. for a refrigerant
Effect of CO2
+ GWP of refrigerant + GWP of insulator
emission while
using
appliance
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
• Can get good representation of past climate
change using greenhouse gases and aerosols
What is there still to do?
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Aerosols
Biosphere feedbacks
Regional climate change
Parameterisations for climate models
“ Real knowledge is to know the extent of
one’s ignorance”
Confucius
Pollution: 1
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“Smog” including ozone
Particulates “PM10”
Acid rain
Primary and secondary
Heat
sources of pollutants: adverse
effects of secondary
(Noise)
pollutants are often more
severe
Pollution: 2
• Short -term and long-term risks from
exposure
• Short-term: eye irritation, asthma
• Long term: strain on immune system,
cancer
• Effects of anthropogenic pollution extend
beyond the immediate urban area
Pollution sources
• Combustion - CO2, CO, NOx, SO2, H2O +
unburnt hydrocarbons
• Emissions from cars are important in
formation of photochemical smog
• Low temperature sources: e.g. leakage from
natural gas lines, evaporation of solvents,
fertilisers, refrigerants and electronics
industry
• Compared by “emission factor”
Classical (or London) “smog”
• Smoke+fog - heavily polluted air in cities
due to SO2 and aerosols from fossil fuel
burning
• Infamous London smog of 1952: 4 days and
implicated in death of 4000 people (but may
have been due to coincident low
temperatures)
• very rare since air pollution regulations
Formation of “London smog”
Fog droplets form on smoke aerosols
SO2 absorbs into these droplets
SO2 oxidised to form sulphuric acid
Photochemical “Los Angeles”
smog
Hydrocarbons and NOx from
vehicles
From Hobbs (2000)
+
sunlight
+
stagnant weather conditions
High concentrations of nitrogen oxides, ozone, CO, aldehydes
New “winter” smog
• High levels of NO2 resulting from vehicle
emissions of NO, low temperatures and
stagnant meteorology
Pollution meteorology
• Usually the atmosphere can disperse even
quite high emissions of pollutants
• Calm conditions, valleys and coastal areas
are particularly at risk due to local
circulations
• Vertical movement is controlled by
temperature profile of atmosphere (e.g.
inversions)
Air pollution disasters
Meuse Valley,
Belgium, 1930
Mortality and
Morbidity
Age groups
affected
Deaths: 60
Ill: 6000
elderly
Donora
Pennsylvania
1948
Deaths:15
Ill: 5900
elderly
Weather
Anticyclonic
inversion and
fog
River valley
Anticyclonic
inversion and
fog
River valley
Nocturnal
inversion, low
winds
coastal
Anticyclonic
inversion and
fog
River plain
Nocturnal low
winds
Steel and zinc
manufacture
Steel and zinc
manufacture
Domestic coal
burning
Fracturing of
tank (accident)
Vehicles
SO2, smoke
SO2, smoke
Sulphur
recovery
(accident)
H2O
SO2, smoke
Methylisocyanide
NO2, particles
Geographical
Setting
Sources
Pollutants
Pozo Rico,
Mexico, 1950
London, UK
1952
Bhopal, India
1984
London, UK,
1991
Deaths: 22
Deaths: 2500?
Ill: 10000?
Deaths: 160
All ages
Deaths: 4000
Ill: > 20000
Elderly at first
Patients with
respiratory
illnesses
Anticyclonic
inversion and
fog as in 1952
River valley
Particulates, PM10
• Released again from fossil fuel burning
(and dust associate with vehicles)
• Can stick to lung walls if inhaled (especially
if charged particles)
• Concentrations are often higher inside cars
in heavy traffic than by the side of the road
due to air intake into cars.
Acid rain
• Key environmental issue in 1980s
• Rainfall of very low pH value or dry
deposition of acidic gaseous and particulate
constituents
• Usually attributed to SO2 from fossil fuel
burning or nitrogen oxide emissions and
often falls at great distance from source
• Countries with high rainfall (e.g. Sweden)
most at risk
Other pollution
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•
•
•
Heat
Noise
indoor pollution
“global” pollution (as in greenhouse gases
etc)