Climate Change and Air Quality

Transcription

1 Climate Change and Air Quality SW PA Air Quality Action June 6, 2007 Peter J. Adams Associate Professor Civil and Environmental Engineering Engineering and Public Policy

2 Outline Climate Change Primer What we know, what we don t Airborne Particulate Matter effects on climate Climate Change effects on air pollution

3 Earth s Energy Balance Solar Energy In Short wave (mostly visible) electromagnetic radiation Terrestrial Energy Out Long wave (invisible) electromagnetic radiation 235 Watts per square meter (W/m 2 ) 235 Watts per square meter (W/m 2 ) If energy in equals energy out, temperature stays the same

4 (Natural) Greenhouse Effect 0 ºF (-18 ºC) Atmosphere Greenhouse gases absorb then re-emit some of the energy leaving Surface 60 ºF (15 ºC)

5 (Enhanced) Greenhouse Effect Atmosphere Human activities emit extra greenhouse gases +2.5 Watts per sq meter Surface

6 Climate Forcing Forcing: Any change in the Earth s energy balance, incoming or outgoing, imposed by humans or another external factor (e.g. sun) Example: change in sun intensity Normal year: 235 W/m 2 Intense year: 236 W/m 2 Climate Forcing = 236 W/m W/m 2 = +1 W/m 2

7 Climate Forcing Forcing: Any change in the Earth s energy balance, incoming or outgoing, imposed by humans or another external factor (e.g. sun) Climate forcings that warm Earth are positive More incoming energy (as in example) Less outgoing energy Climate forcings that cool Earth are negative Less incoming energy More outgoing energy Climate forcings measured in Watts per square meter (W/m 2 )

8 Greenhouse Gases (GHGs) *Nitrous Oxide (N 2 O): 0.15 W/m 2 Agricultural activities (synthetic fertilizers, livestock) and biomass burning Chlorofluorocarbons (CFCs): 0.35 W/m 2 Refrigerants, aerosol propellants banned by international agreements *Methane (CH 4 ): 0.5 W/m 2 Agriculture, natural gas refining, landfills *Carbon Dioxide (CO 2 ): 1.5 W/m 2 Fossil fuel combustion (coal, oil, natural gas, most electricity) and deforestation Energy use is #1 issue *indicates there are also natural sources of this compound

9 Anthropogenic greenhouse gases (well known) Source: IPCC Third Assessment Report

10 Climate Response Response: How much climate changes because of a given forcing People care about temperature/rainfall more than forcings Scientists predict 2.5 F to 10.5 F temperature increase by 2100 from global warming If forcing is well known why is response so uncertain?

11 Simplest Climate Model 3.5 Temperature Change (K) High sensitivity Low sensitivity Forcing (W m -2 )

12 Climate Sensitivity Sensitivity: How much climate would change for a given change in energy in/out (i.e. response per forcing) A major goal of climate models is to determine the sensitivity of the Earth to change Climate sensitivity is currently not very well known Low estimate: 0.3 C per W/m 2 High estimate: 1 C per W/m 2 Low sensitivity: Earth s climate is stable, resists change, tends to return to current state High sensitivity: Climate is unstable, amplifies small changes

13 Climate Feedbacks: A Domino Effect More CO 2 More evaporation Higher temperature Less snow and ice EASY HARD More water vapor More clouds? Darker planet Still higher temperature Smaller temperature increase? Still higher temperature + feedback - feedback? + feedback

14 Climate Feedbacks There is a direct correspondence between feedbacks and climate sensitivity Positive feedbacks imply More warming than initially expected High climate sensitivity Bad news Negative feedbacks imply Less warming than expected Low climate sensitivity Good news Determing how much warming will happen (i.e. climate sensitivity) means we must understand feedbacks

15 Summary: Primer Forcing is a change in amount of energy entering or leaving Earth KNOWN: Forcing from greenhouse gases is 2.5 W/m 2 (+/- 10%) We care about climate response (e.g. how much temperature changes) UNCERTAIN: Sensitivity of climate to our forcings (0.3 to 1.0 ºC per W/m 2 forcing) Sensitivity depends on feedbacks : response of sea ice, water vapor, clouds etc Climate models do not agree on what sensitivity is

16 Outline Climate Change Primer What we know, what we don t Airborne Particulate Matter effects on climate Climate Change effects on air pollution

17 Source: IPCC Third Assessment Report

18 Aerosols Scattering Sunlight Dust and smoke over Australia (Terra)

19 Aerosols Absorbing Sunlight photo courtesy of Jay Apt Kuwaiti oil fires

20 Aerosols and Clouds AVHRR satellite false color image Rosenfeld, Science (2000) Power plant Lead smelter Port Oil refineries Blue: clear sky Red: darker clouds (large droplets) Green: brighter clouds (small droplets)

21 Aerosols and Clouds Aerosol Particles Cloud Droplets Clean Air Polluted Air Brighter, more persistent clouds

22 Source: IPCC Third Assessment Report Example: Total forcing on climate cloud be 2.5 W/m 2 (GHG) + 0 W/m 2 (particles) = +2.5 W/m W/m 2 (GHG) + -2 W/m 2 (particles) = +0.5 W/m 2

23 Aerosols and Climate Uncertainty Aerosol + GHG forcing GHG forcing High sensitivity Temperature Change (K) ?? Low sensitivity th century T increase Forcing (W m -2 )

24 Summary Airborne Particles Airborne particles (aerosols) influence climate Absorb/reflect sunlight Determine cloud brightness and precipitation Forcings associated with particles are much more uncertain than greenhouse gases Greenhouse gases: 2.5 W/m 2 (+/- 10%) Particles and cloud brightness: 0 to -2 W/m 2 Total forcing (particles plus greenhouse gases) to date is uncertain Complicates effort to use past as a climate experiment to measure senstivity

25 Outline Climate Change Primer What we know, what we don t Airborne Particulate Matter effects on climate Climate Change effects on air pollution

26 Ozone with T +2.5K Additional sensitivity study with T effect on PAN chemistry alone gave very similar results Change in MDA8 ozone (ppb) with +2.5 K (uniform)

27 Seasonal Ozone Response Episode probability (%)

28 Winter PM2.5 with T +2.5K PM 2.5 Nitrate Total PM 2.5

29 Nitrate: Humidity +10% (July)

30 Summary Climate and Air Pollution All aspects of air pollution depend on weather and climate Climate change almost certainly will make ozone pollution worse over next ~50 years higher temperature natural and anthropogenic VOC emissions stagnation episodes Harder to say effect of PM pollution temperature affects PM species differently rainfall changes important but hard to predict

31 Conclusions Climate change greenhouse warming real, well understood magnitude of climate (temperature) response harder to predict but still significant Airborne particulate matter (PM) scatters/absorbs sunlight affects cloud properties probably significant net cooling on climate Climate change will make ozone pollution worse will probably have significant effect on PM but harder to quantify