1. Climate change and pollution
Eleanor J Highwood
Department of Meteorology, University of Reading
MSc Intelligent Buildings April 2002

2. Outline: climate change
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?

3. “Climate is what we expect, weather is what we actually get”
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.

4. Has climate changed in the recent past?
Temperature changes
Sea level rise
Precipitation changes
Mountain glaciers
Snow cover

5. 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

6. 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.

7. Variation of warming with time period IPCC 2001

8. Seasonal variation in warming IPCC 2001

9. Temperature changes: 3
Over the period 1950 to 1993, diurnal temperature range has reduced because the nights have warmed more than the days.

10. Sea level changes
Observed rise of m during 20th century. Rises are of order 2mm/year
Mostly due to thermal expansion of oceans

11. Precipitation changes
 over land in tropics and mid-latitudes and  in the subtropics.
NH mid-latitudes have seen an increase of 2-4% in frequency of heavy precipitation events

12. Mountain glaciers
Shrinkage of many glaciers since If it reaches the oceans this contributes to sea-level rise.

13. Snow cover
10% reduction in NH snow cover between 1960s and present day

14. Sea ice
NH sea ice extent has decreased by 10-15% since 1950s

15. 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

16. Changes over past 1000 years (from Mann et al 1999

17. Natural variability:1
There have been large changes in temperature in the past

18. Natural variability:2
Even a climate with no forcing has a lot of variability (IPCC 2001)

19. 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)

20. Fundamental processes
Many interacting components

21. Energy balance S0 (1- p) re2 = 4 re2  Te4
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).

22. Radiation and climate
IPCC 2001

23. The “natural greenhouse effect”
Ta4
Ts4
Ta4
Atmosphere absorbs radiation from ground and re-emits less radiation since it is colder (=0.77)
Earth radiates to space
Atmosphere traps radiation and warms surface so that life can exist.

24. 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.

25. 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

26. Radiative forcing due to  in carbon dioxide
ASR = OLR
System in balance
OLR < ASR
OLR must increase again to balance ASR, so system must warm up. F +ve
CO2 raises  so more radiation comes from cold atmosphere so OLR increases

27. Possible causes of climate change

28. Natural climate change
Solar variability
Volcanic eruptions

29. Solar variability: 1 Changes in the Suns strength
11 year cycle with sunspots
small changes

30. 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

31. 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? )

33. Observed effect on T
IPCC 2001
El Chichon
Pinatubo

34. Anthropogenic causes Greenhouse gases
Ozone changes (stratospheric and tropospheric)
Tropospheric aerosols
Surface albedo changes
Heat pollution

35. 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

37. Greenhouse gases: 2 CO2 (carbon dioxide) CH4 (methane)
N2O (nitrous oxide)
CFCs/HCFCs/HFCs (chlorofluorocarbons/hydrochlorofluorocarbons/hydrofluorocarbons)

38. Strengths of greenhouse gases

39. CO2 :1
Risen by 31% since 1750, roughly in line with emissions from fossil fuel burning

40. 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

41. Carbon cycle

42. CH4 :1
Increased by 50% since 1750 and continues to increase.

43. 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”)

44. N2O Increased by 17% Unprecedented in past 1000 years
Half of current emissions are anthropogenic (fertilisers etc)

45. 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

46. HFCs
No chlorine (therefore don’t affect ozone layer)

47. 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

48. Emission of CFCs etc

49. CF4
SF6

50. 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)

51. Tropospheric ozone changes

52. 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)

53. Aerosols: Direct solar effect
Aerosols scatter and absorb solar radiation
No aerosol
Scattering aerosol
Absorbing aerosol

54. Aerosols: Direct terrestrial effect
Large aerosols (e.g. dust or sulphuric acid in the stratosphere) behave like greenhouse gases.
Aerosol absorbs radiation from ground and re-emits a smaller amount up and down
No aerosol: ground emits to space

55. Aerosols: Indirect effects
Some aerosols can alter the properties of clouds, changing their reflectivity or lifetime

56. Aerosol forcing
Magnitude and sign of forcing depends on distribution and mixing
Very spatially non-uniform distributions

57. 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

58. CO2 vs aerosol forcing
CO2
Sulphates

59. Land albedo changes
Land use changes alter the albedo and the amount of solar radiation reflected back to space.

60. Heat pollution
Urban and industrial regions output large amounts of local heat.
Important regionally and may modify the circulation

61. Radiative forcing since 1750
GHG: Wm-2 (60% CO2, 20% CH4)
Tropospheric ozone: Wm-2
Stratospheric ozone: Wm-2
Tropospheric aerosols (direct):
sulphates (-0.4 Wm-2), biomass (-0.2 Wm-2), organics (-0.1 Wm-2), black carbon (+0.2 Wm-2), dust ?
Indirect effect: -0 to -2 Wm-2
Solar: +/- 0.2 Wm-2

62. 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.

63. Water vapour - temperature feedback
 T (e.g. due to CO2)
Water vapour is a greenhouse gas, therefore
More evaporation at the surface
+ve feedback
More water vapour in the atmosphere

64. Snow/ice - temperature feedback
 T (e.g. due to CO2)
More solar energy is absorbed at the surface, therefore
Less snow and ice
+ve feedback
Planetary albdeo increases

65. 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?

66. Other feedbacks
biosphere

67. 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

68. 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

69. Model validation Simulate present day climate
Individual components such as radiation / convection
Simulate past climates of Earth
Simulate climates of other planets

71. Hierarchy of models 0 dimensions (e.g. simple energy balance model)
Latitude - altitude
(chemistry models)
Latitude - longitude
(paleoclimate models)
3-D models
Coupled atmosphere/ocean models
“slab ocean”

72. Types of experiments “Equilibrium 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.
“Transient response”
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.

73. Temperature changes

74. 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.

75. Future temperature changes
Increases in global mean temperature of 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

76. T
Precip.

77. 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

78. 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

79. Other future changes: 2
Change in frequency and duration of extreme events
Possible but very uncertain changes in weather events

80. 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

81. 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)

82. Percentage change in average crop yields for the climate change scenario:
wheat, maize and rice.
(From Met Office)

83. Change in natural vegetation type
(From Met. Office)

84. Change in water stress, due to climate change, in countries using more than 20% of their potential water resources
(From Met Office)

85. Potential transmission of malaria
a) baseline climate conditions ( )
b) climate change scenario for the 2050s.
(From Met Office)

86. 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

87. Mitigation vs adaptation?
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

88. Timescale for future change
10s/100s yrs
~ 100 years
100s / 1000 yrs
Stabilised
CO2 concs in the atmosphere
Stabilised surface temperature
Stabilised sea level
Stabilised emissions
Any response to changes we make will be very slow.

89. 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?

90. 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 emission while using appliance
+ GWP of refrigerant + GWP of insulator

91. 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

92. What is there still to do?
Aerosols
Biosphere feedbacks
Regional climate change
Parameterisations for climate models
“ Real knowledge is to know the extent of one’s ignorance”
Confucius

93. Pollution: 1 “Smog” including ozone Particulates “PM10” Acid rain Heat
(Noise)
Primary and secondary sources of pollutants: adverse effects of secondary pollutants are often more severe

94. 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

95. 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”

96. 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

97. Formation of “London smog”
Fog droplets form on smoke aerosols
SO2 absorbs into these droplets
SO2 oxidised to form sulphuric acid

98. Photochemical “Los Angeles” smog
From Hobbs (2000)
Hydrocarbons and NOx from vehicles +
sunlight
stagnant weather conditions
High concentrations of nitrogen oxides, ozone, CO, aldehydes

99. New “winter” smog
High levels of NO2 resulting from vehicle emissions of NO, low temperatures and stagnant meteorology

100. 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)

101. Air pollution disasters

102. 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.

103. 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

104. Other pollution Heat Noise indoor pollution
“global” pollution (as in greenhouse gases etc)