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

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Presentation on theme: "Climate change and pollution Eleanor J Highwood Department of Meteorology, University of Reading MSc Intelligent Buildings April 2002."— Presentation transcript:

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 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 Earths 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 Solar energy absorbed by the Earth-atmosphere system = Energy radiated from Earth- Atmosphere system to space 30% of incoming solar radiation reflected to space by clouds, surface, molecules and particles in the atmosphere (albedo). S 0 (1- p ) r e 2 = 4 r e 2 T e 4

22 Radiation and climate IPCC 2001

23 The natural greenhouse effect Earth radiates to space Atmosphere absorbs radiation from ground and re-emits less radiation since it is colder ( =0.77) T s 4 T a 4 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 CO 2 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 dont 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 CO 2 (carbon dioxide) CH 4 (methane) N 2 O (nitrous oxide) CFCs/HCFCs/HFCs (chlorofluorocarbons/hydrochlorofluorocarb ons/hydrofluorocarbons)

38 Strengths of greenhouse gases

39 CO 2 :1 Risen by 31% since 1750, roughly in line with emissions from fossil fuel burning

40 CO 2 :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 CH 4 :1 Increased by 50% since 1750 and continues to increase.

43 CH 4 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 N2ON2O 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 dont affect ozone layer)

47 HFCs No chlorine (therefore dont 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 CF 4 SF 6

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 aerosolScattering aerosolAbsorbing aerosol

54 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

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 CO 2 vs aerosol forcing CO 2 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% CO 2, 20% CH 4 ) 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 CO 2 ) More evaporation at the surface More water vapour in the atmosphere Water vapour is a greenhouse gas, therefore +ve feedback

64 Snow/ice - temperature feedback T (e.g. due to CO 2 ) Less snow and ice Planetary albdeo increases More solar energy is absorbed at the surface, therefore +ve feedback

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 - cant 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 - longitude (paleoclimate models) Latitude - altitude (chemistry models) 3-D models slab ocean Coupled atmosphere/ocean models

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 TPrecip.

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 Legislation Mitigation vs adaptation? To prevent any further rise in CO 2 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 Stabilised emissions Stabilised CO 2 concs in the atmosphere Stabilised surface temperature Stabilised sea level 10s/100s yrs~ 100 years 100s / 1000 yrs Any response to changes we make will be very slow.

89 Kyoto Protocol Reduction of emissions of CO 2, CH 4, N 2 O and basket of 6 gases which includes SF 6 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 CO 2 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 ones 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 - CO 2, CO, NO x, SO 2, H 2 O + 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 SO 2 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 Fog droplets form on smoke aerosols SO 2 absorbs into these droplets SO 2 oxidised to form sulphuric acid Formation of London smog

98 Photochemical Los Angeles smog Hydrocarbons and NO x from vehicles + sunlight + stagnant weather conditions High concentrations of nitrogen oxides, ozone, CO, aldehydes From Hobbs (2000)

99 New winter smog High levels of NO 2 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 SO 2 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)

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