Climate change and pollution

Eleanor J Highwood

Department of Meteorology, University of Reading

MSc Intelligent Buildings April 2002

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?

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?

• Temperature changes

• Sea level rise

• Precipitation changes

• Mountain glaciers

• Snow cover

Temperature changes 1Global 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 mid-latitudes 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

30% of incoming solar radiation reflected to space by clouds, surface, molecules and particles in the atmosphere (albedo).

S0 (1- p) re2 = 4 re

2 Te4

Radiation and climate

IPCC 2001

The “natural greenhouse effect”

Earth radiates to spaceAtmosphere absorbs radiation from ground and re-emits less radiation since it is colder (=0.77)

Ts

4

Ta4

Ta4

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 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

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

VolcanoesLarge 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

• CO2 (carbon dioxide)

• CH4 (methane)

• N2O (nitrous oxide)

• CFCs/HCFCs/HFCs (chlorofluorocarbons/hydrochlorofluorocarbons/hydrofluorocarbons)

Strengths of greenhouse gasesGas Lifetime

(years)Forcing perppbv (Wm-2)

Forcing so far(Wm-2)

GWP rel. toCO2 (100 yrs)

GWP rel. toCO2 (500 yrs)

CO2 Variable 1.8x10-5 1.56 1 1CH4 12.2 3.7 x 10-4 0.46 21 6.5N2O 120 3.7 x 10-3 0.14 310 170HFC-23 264 0.18 11700 9800HFC-32 5.6 0.11 650 200HFC-41 3.7 0.02 150 45HFC-125 32.6 0.20 1300 920HFC-134a 14.6 0.17 1300 420SF6 3200 0.64 0.002 239000 34900CF4 50000 0.10 0.007 6500 10000C2F6 10000 0.23 9200 14000C3F8 2600 0.24 7000 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:– 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• 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 Wm-2), 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)

More evaporation at the surface

More water vapour in the atmosphere

Water vapour is a greenhouse gas, therefore

+ve feedback

Snow/ice - temperature feedback

T (e.g. due to CO2)

Less snow and ice

Planetary albdeo increases

More solar energy is absorbed at the surface, therefore

+ve feedback

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 - longitude

(paleoclimate models)

Latitude - altitude

(chemistry models)

3-D models

“slab ocean”Coupled atmosphere/ocean models

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.

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 (1961-1990)

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

Stabilised emissions

Stabilised

CO2 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.

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 emission while using appliance

+ GWP of refrigerant + GWP of insulator

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?

• Aerosols

• Biosphere feedbacks

• Regional climate change

• Parameterisations for climate models

“ Real knowledge is to know the extent of one’s ignorance”

Confucius

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

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

Fog droplets form on smoke aerosols

SO2 absorbs into these droplets

SO2 oxidised to form sulphuric acid

Formation of “London smog”

Photochemical “Los Angeles” smog

Hydrocarbons and NOx from vehicles

+

sunlight

+

stagnant weather conditions

High concentrations of nitrogen oxides, ozone, CO, aldehydes

From Hobbs (2000)

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 disastersMeuse Valley,Belgium, 1930

DonoraPennsylvania1948

Pozo Rico,Mexico, 1950

London, UK1952

Bhopal, India1984

London, UK,1991

Mortality andMorbidity

Deaths: 60Ill: 6000

Deaths:15Ill: 5900

Deaths: 22 Deaths: 4000Ill: > 20000

Deaths: 2500?Ill: 10000?

Deaths: 160

Age groupsaffected

elderly elderly All ages Elderly at first Patients withrespiratoryillnesses

Weather Anticyclonicinversion andfog

Anticyclonicinversion andfog

Nocturnalinversion, lowwinds

Anticyclonicinversion andfog

Nocturnal lowwinds

Anticyclonicinversion andfog as in 1952

GeographicalSetting

River valley River valley coastal River plain River valley

Sources Steel and zincmanufacture

Steel and zincmanufacture

Sulphurrecovery(accident)

Domestic coalburning

Fracturing oftank (accident)

Vehicles

Pollutants SO2, smoke SO2, smoke H2O SO2, smoke Methyl-isocyanide

NO2, particles

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

• Heat

• Noise

• indoor pollution

• “global” pollution (as in greenhouse gases etc)