Kyra Naumoff Shields, PhDAlbedo • percentage of solar energy reflected back by a surface Blackbody...
Transcript of Kyra Naumoff Shields, PhDAlbedo • percentage of solar energy reflected back by a surface Blackbody...
Kyra Naumoff Shields, PhD ([email protected])
March 30, 2011
Based on text from: Chemical Fate and Transport in the Environment
1
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
5
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
6
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
7
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
9
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
10
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
16
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
18
Uncertainties considerable (MISSING C)
Anthropogenic CO2 fluxes are a significant
fraction of natural ones
19
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)
20
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]
21
22
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)
24
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
26
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
31
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)
34
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
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
37
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
38
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
40
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
44
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
45
Source: http://unfccc.int/kyoto_protocol/items/2830.php
#40
#14
46