Presentation on theme: "Climate change and pollution"— Presentation transcript:
1Climate change and pollution Eleanor J HighwoodDepartment of Meteorology, University of ReadingMSc Intelligent Buildings April 2002
2Outline: 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 oftemperature, precipitation, radiation, clouds, snow cover etc.
4Has climate changed in the recent past? Temperature changesSea level risePrecipitation changesMountain glaciersSnow cover
5Temperature changes 1Global mean T of air at Earth’s surface has by 0.6 +/- 0.2 C over the 20th century.IPCC 2001
6Temperature changes: 2Regional 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.
9Temperature changes: 3Over the period 1950 to 1993, diurnal temperature range has reduced because the nights have warmed more than the days.
10Sea level changesObserved rise of m during 20th century. Rises are of order 2mm/yearMostly due to thermal expansion of oceans
11Precipitation 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
12Mountain glaciersShrinkage of many glaciers since If it reaches the oceans this contributes to sea-level rise.
13Snow cover10% reduction in NH snow cover between 1960s and present day
14Sea iceNH sea ice extent has decreased by 10-15% since 1950s
15Have changes been unusual? Proxy records:tree rings (past 100 years)shallow ice corescoralsdeep sea sediments (past 10, 000 years)Natural variability: changes resulting from interactions between components of climate system
16Changes over past 1000 years (from Mann et al 1999
17Natural variability:1There have been large changes in temperature in the past
18Natural variability:2Even a climate with no forcing has a lot of variability (IPCC 2001)
19What 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)
20Fundamental processes Many interacting components
21Energy balance S0 (1- p) re2 = 4 re2 Te4 Solar energy absorbed by the Earth-atmosphere systemEnergy radiated from Earth- Atmosphere system to space=S0 (1- p) re2 = 4 re2 Te430% of incoming solar radiation reflected to space by clouds, surface, molecules and particles in the atmosphere (albedo).
23The “natural greenhouse effect” Ta4Ts4Ta4Atmosphere absorbs radiation from ground and re-emits less radiation since it is colder (=0.77)Earth radiates to spaceAtmosphere traps radiation and warms surface so that life can exist.
24Radiative forcing, FRadiative 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.
25Radiative forcing due to in solar output ASR = OLRSystem in balanceASR > OLROLR must increase to balance ASR, so system must warm up. F +ve
26Radiative forcing due to in carbon dioxide ASR = OLRSystem in balanceOLR < ASROLR must increase again to balance ASR, so system must warm up. F +veCO2 raises so more radiation comes from cold atmosphere so OLR increases
28Natural climate change Solar variabilityVolcanic eruptions
29Solar variability: 1 Changes in the Suns strength 11 year cycle with sunspotssmall changes
30Solar variability: 2 Changes in Sun-Earth geometry Sun-Earth distance, tilt of Earth and ellipse of orbitact over very long timescales, many thousands of yearspossibly play a role in inducing ice ages but not important on past 250 years time scaleat current time provides a cooling influence on climate
31VolcanoesLarge eruptions like Pinatubo (1991) put clouds of sulphur dioxide gas into stratosphere, above the weather.cloud of sulphuric acid droplets scatter and absorb solar radiationcooling of surface and warming of stratosphereBut, aerosols only last a few years, so generally climate impact only lasts a few years (apart from cumulative effect? )
35Greenhouse gases: 1Water vapour is most important natural greenhouse gas, but we don’t usually change it directlyStrength of a greenhouse gas depends onstrength of absorption of infra-red radiationoverlap of absorption with other gaseslifetime in the atmosphereamount added over given period of time
42CH4 :1Increased by 50% since 1750 and continues to increase.
43CH4Current concentrations have not been exceeded in 420 thousand yearsFrom rice-growing, domestic cattle, waste disposal and fossil fuel burning12 year lifetime (a quick-fix for “global warming”)
44N2O Increased by 17% Unprecedented in past 1000 years Half of current emissions are anthropogenic (fertilisers etc)
45CFCsCFCs 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
47HFCs No chlorine (therefore don’t affect ozone layer) BUT they are powerful greenhouse gases and very long-livedEntirely anthropogenic in origin (and used in a variety of odd ways!)Rising quickly in the atmosphere
50Ozone Spatially non-uniform Radiative forcing depends critically on level at which ozone changes:troposphere: ozone has increased and produces a positive radiative forcingstratosphere: 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)
52Tropospheric 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)
53Aerosols: Direct solar effect Aerosols scatter and absorb solar radiationNo aerosolScattering aerosolAbsorbing aerosol
54Aerosols: 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 downNo aerosol: ground emits to space
55Aerosols: Indirect effects Some aerosols can alter the properties of clouds, changing their reflectivity or lifetime
56Aerosol forcingMagnitude and sign of forcing depends on distribution and mixingVery spatially non-uniform distributions
57Aerosol forcingCannot be used to cancel out greenhouse gas forcing (patterns are completely different)Response may also be differentIndirect effect is very uncertain but potentially large
62Can we model climate change? At the simplest level we can relate:T=FBut what is ? Represents feedbacks between climate components.Many feedbacks, three very important ones.
63Water vapour - temperature feedback T (e.g. due to CO2)Water vapour is a greenhouse gas, thereforeMore evaporation at the surface+ve feedbackMore water vapour in the atmosphere
64Snow/ice - temperature feedback T (e.g. due to CO2)More solar energy is absorbed at the surface, thereforeLess snow and ice+ve feedbackPlanetary albdeo increases
65Cloud feedbackClouds 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 climatepositive or negative feedback?
67Climate modelling We use climate models to: model present day climate and understand physical processesmodel past climate and attribute change to particular mechanismspredict future climate change
68Types 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
69Model validation Simulate present day climate Individual components such as radiation / convectionSimulate past climates of EarthSimulate climates of other planets
71Hierarchy of models 0 dimensions (e.g. simple energy balance model) Latitude - altitude(chemistry models)Latitude - longitude(paleoclimate models)3-D modelsCoupled atmosphere/ocean models“slab ocean”
72Types 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.
74What 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.
75Future temperature changes Increases in global mean temperature of C by the year 2100Greater warming over land than over ocean, especially in North America and northern and central Asia during the cold seasonProbably an increase in number of hot days and decrease in cold daysNight-time increase more than day-time
77Future sea level changes Rise by a further 0.09 to 0.88m by the year 2100Half of this rise comes from thermal expansion, remainder from melting glaciers and the Greenland ice sheet
78Other future changes:1Increases in global averages and variability of both precipitation and evaporation (NH mid-lats more rain than snow)Increased summer heating decreases soil moisturerecent trends for SST patterns to become more El Nino -like
79Other future changes: 2Change in frequency and duration of extreme eventsPossible but very uncertain changes in weather events
80ImpactsIncreases in heatwaves - increase in mortality due to heat stressfloodingcoastal erosionagricultural yields decrease in placesextension of desertificationpressure on water resourcesspread of disease and pest to new areas
81The 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)
82Percentage change in average crop yields for the climate change scenario: wheat, maize and rice.(From Met Office)
83Change in natural vegetation type (From Met. Office)
84Change in water stress, due to climate change, in countries using more than 20% of their potential water resources(From Met Office)
85Potential transmission of malaria a) baseline climate conditions ( )b) climate change scenario for the 2050s.(From Met Office)
86Impacts for the UK Much harder to predict regional climate change Northwards shift of vegetation by 50-80km per decadeimpacts on wildlife, soils, water resources and agriculture in South
87Mitigation vs adaptation? LegislationMitigation 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
88Timescale for future change 10s/100s yrs~ 100 years100s / 1000 yrsStabilisedCO2 concs in the atmosphereStabilised surface temperatureStabilised sea levelStabilised emissionsAny response to changes we make will be very slow.
89Kyoto ProtocolReduction of emissions of CO2, CH4, N2O and “basket of 6 gases” which includes SF6 and several of the HFCsRole of carbon sinks uncertainRatification (particularly by US)?Role of developing nations?
90Measures for Kyoto Protocol Global Warming Potentials (accounts for strength and lifetime of greenhouse gases)Total Equivalent Warming Impact (TEWI)e.g. for a refrigerantEffect of CO2 emission while using appliance+ GWP of refrigerant + GWP of insulator
91What have we found so far? Climate change is unlikely to be solely the result of either natural or anthropogenic effectsComplexity is still an issue, especially interaction of biosphere and other componentsCan get good representation of past climate change using greenhouse gases and aerosols
92What is there still to do? AerosolsBiosphere feedbacksRegional climate changeParameterisations for climate models“ Real knowledge is to know the extent of one’s ignorance”Confucius
93Pollution: 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
94Pollution: 2 Short -term and long-term risks from exposure Short-term: eye irritation, asthmaLong term: strain on immune system, cancerEffects of anthropogenic pollution extend beyond the immediate urban area
95Pollution sourcesCombustion - CO2, CO, NOx, SO2, H2O + unburnt hydrocarbonsEmissions from cars are important in formation of photochemical smogLow temperature sources: e.g. leakage from natural gas lines, evaporation of solvents, fertilisers, refrigerants and electronics industryCompared by “emission factor”
96Classical (or London) “smog” Smoke+fog - heavily polluted air in cities due to SO2 and aerosols from fossil fuel burningInfamous 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
97Formation of “London smog” Fog droplets form on smoke aerosolsSO2 absorbs into these dropletsSO2 oxidised to form sulphuric acid
98Photochemical “Los Angeles” smog From Hobbs (2000)Hydrocarbons and NOx from vehicles+sunlightstagnant weather conditionsHigh concentrations of nitrogen oxides, ozone, CO, aldehydes
99New “winter” smogHigh levels of NO2 resulting from vehicle emissions of NO, low temperatures and stagnant meteorology
100Pollution meteorology Usually the atmosphere can disperse even quite high emissions of pollutantsCalm conditions, valleys and coastal areas are particularly at risk due to local circulationsVertical movement is controlled by temperature profile of atmosphere (e.g. inversions)
102Particulates, PM10Released 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.
103Acid rain Key environmental issue in 1980s Rainfall of very low pH value or dry deposition of acidic gaseous and particulate constituentsUsually attributed to SO2 from fossil fuel burning or nitrogen oxide emissions and often falls at great distance from sourceCountries with high rainfall (e.g. Sweden) most at risk