Kyra Naumoff Shields, PhD (kshields@pitt.edu)

March 30, 2011

Based on text from: Chemical Fate and Transport in the Environment

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Describe & understand: • Radiation balance of Earth • Radiative Forcing • Long-Lived GHG Water vapor

Carbon dioxide

Methane

CFCs

• Short-Lived GHG Nitrous oxide

Ozone

Fine aerosol particles

Black carbon

2

Earth’s temperature – balance btwn solar radiation input and reflection and reradiation of energy from Earth and its atmosphere back to space (figure 2-30)

3 Source: http://www.uwsp.edu/geo/faculty/ritter/images/atmosphere/energy/radiation_balance_usgs_large.jpg

4

Source: http://www.uwsp.edu/geo/faculty/ritter/images/atmosphere/energy/radiation_balance_usgs_large.jpg

Solar constant ~ 1400 W/m2

Projected area

intercepting the solar radiation is πr2 (r = Earth’s radius)

Earth’s surface area is

4πr2

Mean solar radiation

received outside Earth’s atmosphere is ~1/4 solar constant ~ 350 W/m2

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Source:

http://home.iprimus.com.au/nielsens/solrad.html

Some absorbed by the atmosphere and clouds

Some reflected back into space • Clear skies: ~ 80 to 85% solar radiation reaches Earth

• Cloudy skies: ~50% reaches Earth’s surface

• Generally, ~ a third of solar radiation that reaches Earth’s surface is reflected

Remaining energy is absorbed • Earth’s temperature increases

• Rate of radiation in the long-wave, infrared spectrum increases

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Albedo • percentage of solar energy reflected back by a surface

Blackbody

• Idealized physical body that absorbs all incident energy at all wavelengths

• Stefan-Boltzmann law (J = sigma * T4) (gives rate of reradiation) Where: sigma = Stefan-Boltzmann constant 5.7x10-12 W/(cm2*K4)

T = absolute temperature

Wien’s displacement law • Gives the wavelength of maximum emission

• Product of absolute temperature of a radiating blackbody and the wavelength corresponding to maximum energy (lambda max) is a constant

• Lambda max (cm) * T = 0.29 (T = absolute temperature)

Wave number: reciprocal of wavelength

• In the infrared portion of the spectrum, absorbance data are expressed as a function of reciprocal wavelength

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Values range from 0 for no reflection to 1 for complete reflection of light striking the surface.

• can be expressed as a percentage (albedo multiplied by 100), i.e. grass has an albedo of about .23 aka 23% of it is reflected away.

8 Source: http://www.uwsp.edu/geo/faculty/ritter/images/atmosphere/energy/radiation_balance_usgs_large.jpg

What mean surface temperature would be predicted for Earth if it had no atmosphere? Assume it behaves as a blackbody.

• ~350 W/m2 of solar radiation would be received if atmospheric effects ignored

• Earth reflects ~35% of received radiation

• Use Stefan-Boltzmann law to solve for T

• J = sigma * T4

• T = 251 K or -22°C (estimated Earth surface temp)

What would be the wavelength at which maximum energy is

reradiated by Earth at that temperature? Lambda max = 0.29/251 K = 12µM

What is the corresponding wave number? =1/lambda = 1/0.0012cm = 870/cm

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Not all energy re-radiated by Earth escapes back to space • Annual mean global temp = 15°C (~60°F)

• Atmospheric gases and vapors scatter some of incoming solar radiation & trap long-range infrared radiation and reradiate a fraction of the absorbed energy back to Earth

Source:

http://en.wikipedia.or

g/wiki/File:The_green

_house_effect.svg

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11

Source: http://www.esrl.noaa.gov/gmd/

5 major naturally occurring (long-lived) gases: • Water vapor

• Carbon dioxide CO2

• Ozone O3

• Methane CH4

• Nitrous Oxide NO2

Human activity increased mixing ratios

• Also released other anthropogenic GHG (e.g. CFCs)

Enhanced greenhouse effect – more long-wave

radiation emitted by Earth’s surface is trapped and reradiated back to Earth

• Change in available energy know as radiative forcing

12

Source: http://en.wikipedia.org/wiki/File:Atmospheric_Transmission.png 13

14 Source: http://www.ipcc.ch/pdf/presentations/COP15-presentations/sokona_20091208.pdf

The international standard practice is to express greenhouse gases in carbon dioxide (CO2) equivalents (CO2e)

The Intergovernmental Panel on Climate Change (IPCC) provides the generally accepted values for GWP, which changed slightly between 1996 and 2001

• GWP is defined as the ratio of the time-integrated radiative forcing from the instantaneous release of 1 kg of a trace substance relative to that of 1 kg of a reference gas (i.e. CO2)

• Radiative forcing: metric used for the quantitative comparisons of the strength of different human and natural agents in causing climate change

15

Source: http://www.epa.gov/oms/climate/420f05002.htm

65% of greenhouse effect due to water Not greatly influenced by direct anthropogenic

emissions

Source:

http://en.wikipedia.org/wiki/File:BAMS_clim

ate_assess_boulder_water_vapor_2002.png

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Stratospheric water vapor

measurements show a

statistically significant

increase of approximately

1%/year over altitudes

15-28 km

Further patterning limited

by lack of global long-term

measurements

CO2 absorbs 2nd largest amount of long-wave infrared radiation (~32%) Natural sources - Volcanic eruptions

CO2 stored in ocean sediments & rocks Long-lived (hundreds of years)

Source: http://www.esrl.noaa.gov/gmd/ 17

Source:

http://en.wikipedia.org/wiki/File:Maun

a_Loa_Carbon_Dioxide-en.svg

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Uncertainties considerable (MISSING C)

Anthropogenic CO2 fluxes are a significant

fraction of natural ones

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Some enhanced photosynthesis Unpredictable species change &

replacements Net effect of biotic change?

• Store additional CO in form of organic material & lessen effects of anthropogenic CO2 releases (negative feedback)

• Warmer temps favor decomposition of organic material and increase CO2 release (positive feedback)

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Each additional molecule CH4 absorbs ~20times as much long-wave infrared radiation as a molecule of CO2

Increasing at an annual rate of ~0.01ppm/yr (Figure 4-44) Present for tens of years (i.e. globally mixed) Precursor to tropospheric [ozone]

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Emissions in

teragrams/yr

Natural

sources

include

wetlands,

termites,

oceans, etc.

Biospheric

sources include

enteric

fermentation, rice

paddies, biomass

burning, landfills,

animal waste,

domestic sewage

At higher temps, anaerobic decomposition rates of organic material may accelerate & lead to more CH4 in atmosphere

Large CH4 reservoirs in methane clathrate (crystalline icelike structure of water and CH4) in areas of permafrost and beneath certain marine sediments

23

Source:

http://www.epa.

gov/methane/pr

ojections.html

Each additional molecule N20 absorbs ~10,000 times as much long-wave infrared radiation as a molecule of CO2

Long atmospheric residence time…50 to 1700 years

Exclusive anthropogenic source (Figure 4-47)

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25

Source: http://en.wikipedia.org/wiki/Greenhouse_gas

Intergovernmental Panel on Climate Change Assesses the scientific, technical and socio-economic

information relevant for the understanding of the risk of human-induced climate change

5th Assessment underway

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Source: http://www.ipcc.ch/pdf/presentations/20th%20Anniversary%20BFM/pres-wg-1-ipcc.pdf

27

Source:

IPCC, 2007:

Summary for

Policymakers. In:

Climate Change

2007: The Physical

Science Basis

28 Source: http://ehs.sph.berkeley.edu/krsmith/presentations/HEI%20Apr%2010%20used.pdf

29 Source: http://ehs.sph.berkeley.edu/krsmith/presentations/HEI%20Apr%2010%20used.pdf

30 Source: http://ehs.sph.berkeley.edu/krsmith/presentations/HEI%20Apr%2010%20used.pdf

Ozone (warming) • CO, CH4, NOx, non-methane volatile organic carbons (NMVOCs), NOx, water

vapor, aeorsols, sunlight

Nitrous oxide Fine aerosol particles – scatter solar radiation back to space and

lead to cooling • Sulfate, nitrate, organic carbon

• also modify properties of clouds

• except…

Black Carbon (warming) • Absorbs solar radiation and warms atmosphere

Two Key Sources:

• Smith et al. Public health benefits of strategies to reduce GHG emissions: health implications of short-lived GH pollutants. Lancet 2009

• Unger et al. Attribution of climate forcing to economic sectors. PNAS 2010

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Secondary pollutant formed via photochemical rxns involving nitrogen oxides and VOCs in presence of UV light

Background tropospheric [O3] tripled since pre-industrial times

Very short-lived (hours to days)

32

Source: http://en.wikipedia.org/wiki/Greenhouse_gas

Associated with mortality, morbidity (including asthma exacerbation) and hospital admissions for respiratory causes

Causes effects through 2 primary mechanisms: • Direct oxidative stress

• Damaging the pulmonary system and draining energy from normal cell functions towards defense mechanisms

33 Source: http://www.epa.gov/apti/ozonehealth/population.html

Stable in troposphere but oxidizes to ozone-reactive NO in the stratosphere

Each additional molecule N20 absorbs ~200 times as much long-wave infrared radiation as a molecule of CO2

Increasing at an annual rate of ~0.8ppb(v)/year

Short-lived (days to weeks)

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Nitrification • Oxidation of ammonium (NH4+) to nitrate • Carried out by chemoautotrophic bacteria in oxygenated

environments with NH4+ • Fraction NH4+ converted to N2O is ~<1% (influenced by

pH and [O2]) Stimulated in heavily fertilized agricultural systems

Denitrification • Nitrate is used as an oxidant by organisms in the

degradation of organic material (produces N2O)

• N2O release enhanced by low pH, low temperature, high nitrate

• Influenced by agricultural management practices

35

Source: http://pubs.usgs.gov/fs/fs07203/

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Sulfates are secondary products from transformations of precursor emissions

• Emitted as SO2, converted to sulfate depending on local conditions

Cooling effect –

• May explain why models generally predict given our greenhouse gas emissions, the earth should have warmed considerably more than it has in reality

• Can sometimes be coated with black carbon to make brown carbon, which has warming potential

Dirty, mixed-up and short-lived

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Source: Smith et al. Lancet. 2009

Findings from a meta-analysis showed positive associations between sulphate exposure and daily measures of lung function, symptoms and asthma drug use

Findings from American Cancer Society Cancer Prevention Study II reported increased mortality from all natural causes, cardiopulmonary and cardiovascular disease and lung cancer associated with long-term exposure

• Harvard Six-Cities study reported similar results

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Source:

http://www.ucar.edu/communications/quarterly/summer98/

sulfate.html

Dark colored fine PM containing a large fraction of elemental carbon

Derived exclusively from incomplete combustion

Strongly warming and increase

heat absorption if deposited on snow or ice

• e.g. Himalayan glaciers or in the Arctic

Lifespan is days to weeks and

thus effects depend on local conditions

No official inventories produced

39 Source: Smith et al. Lancet. 2009

Epidemiological evidence linking measured BC and elemental carbon (EC) to health outcomes is scarce • routine government monitoring is not done in sufficient

locations • No standard measurement method

Black carbon and black smoke highly correlated • Black smoke measured using a standard method

Smith et al analysis of black smoke and daily mortality detected significant, positive associations with all-cause, cardiovascular and respiratory mortality

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41 Source: Unger et al 2010.

42 Source: Unger et al 2010.

43 Source: http://en.wikipedia.org/wiki/File:Greenhouse_Gas_by_Sector.png

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Source: Unger et al 2010.

International agreement linked to the United Nations Framework Convention on Climate Change

Major feature of the Kyoto Protocol is that it sets binding targets for 37 industrialized countries and the European community for reducing GHG emissions

• amount to an average of 5% against 1990 levels over the five-year period 2008-2012.

The Kyoto mechanisms are:

• Emissions trading – known as “the carbon market"

• Clean development mechanism (CDM)

• Joint implementation (JI)

By the end of the first commitment period of the Kyoto Protocol in

2012, a new international framework needs to have been negotiated and ratified that can deliver the stringent emission reductions indicated by the IPCC

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Source: http://unfccc.int/kyoto_protocol/items/2830.php

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