Greenhouse Effect:
Earth’s Blanket
What is a greenhouse?
Wikipedia | GNU
Smithsonian
Greenhouse Effect
Process by which thermal radiation from a planetary surface is absorbed by
atmospheric greenhouse gases, and is re-radiated in all directions
What gets in and what is blocked?
© 2011 The Pennsylvania State University
Albedo
 Reflecting power of a




surface
Ratio of reflected radiation
from the surface to
incident radiation upon it
No units
0.3 is the global average
albedo
Why are urban areas
warmer than rural areas?
Surface
Albedo
Fresh Asphalt
0.04
Worn Asphalt
0.12
Conifer forest
(Summer)
0.08 - 0.15
Deciduous trees
0.15 - 0.18
Bare soil
0.17
Green grass
0.25
Desert sand
0.4
New concrete
0.55
Ocean ice
0.5 - 0.7
Fresh snow
0.80 - 0.90
Earth’s Energy Budget
NOAA|NWS
Greenhouse Gas (GHG)
 Gas in an atmosphere that
absorbs and emits radiation
within the thermal infrared
range
 GHG’s in Earth’s atmosphere in
order of abundance





NASA
Water Vapor (H2O)
Carbon Dioxide (CO2)
Methane (CH4)
Nitrous Oxide (N2O)
Ozone (O3)
GHG Concentration
 Depends on rates of emission and rates of
removal
 If emissions increase with time, atmospheric
concentration will increase with time, regardless
of the atmospheric lifespan of the gas
Water Vapor - H2O
Natural Source
•Evaporation of water
•Sublimation of ice
•Plant and animal respiration
Anthropogenic
source
•Evaporation and transpiration losses from watering lawns
Lifespan
•9 days in the atmosphere
Location
•Troposphere
Does it do us any
good?
•Supports life
•Triggers convection currents
•Leads to cloud formation
Carbon Dioxide - CO2
Natural Source
•Animal and plant respiration
•Ocean-atmosphere exchange
•Photosynthesis (sink)
Anthropogenic
source
•Fossil fuel combustion
•Deforestation (lack of sink)
Lifespan
•More than half is removed within a century
•A small fraction (20%) can remain in the atmosphere for
many millenia
Location
•Troposphere
Does it do us any
good?
•Photosynthesis
Methane - CH4
Natural Source
•Wetlands
•Termites
Anthropogenic
source
•Raising ruminant animals (cattle)
•Energy production from coal and natural gas
•Rice agriculture
•Biomass burning
Lifespan
•12 years
•Removed by chemical processes in the atmosphere
Location
•Troposphere
•Stratosphere
Does it do us
any good?
•Helps regulate temperature
Nitrous Oxide - N2O
Natural Source
•Oceans
•Chemical oxidation of ammonia in the atmosphere
•Soils
Anthropogenic
source
•Transformation of fertilizer nitrogen into N2O and its subsequent
emission from agricultural soils
•Biomass burning
•Raising cattle
Lifespan
•110 years
•Destroyed in the stratosphere by solar radiation
Location
•Troposphere
•Stratosphere
Does it do us any
good?
•Helps regulate temperature
Ozone - O3
Natural Source
•Formed when O2 molecule photodissociates after absorbing an IR photon
•Free O molecule bonds with O2 to form O3
Anthropogenic source
•Chlorofluorocarbons (CFC’s) contain molecules which can destroy ozone in the
stratosphere
•Tropospheric ozone formed from reactions with carbon monixide, methane, and other
volitile organic compounds
•Tropospheric ozone is found in smog
Lifespan
•Tropospheric ozone (a few days)
•Stratosphere – long lived due to the oxygen-ozone cycle
Location
•Stratosphere (Ozone Layer)
•Troposphere (harmful)
•Mesosphere
Does it do us any
good?
•Stratospheric ozone protects us from 97-99% of the sun’s UV radiation
Some GHG Concentration Trends
NOAA | accessed via Wikipedia
What if … there were no GHG’s?
 Would Earth be very hot or very cold? … WHY?
VS.
 Would the air be very dry or very wet?
Hint: What is the most abundant GHG?
Goldilocks Principle
Earth … Just Right
Venus … Too Hot
Mars .. Too Cold
 Extremely dense
 Almost no atmosphere
 Perfect atmosphere to
atmosphere
 High concentration of
CO2
 High surface
temperature of 464˚C
 Low concentration of
sustain life
 Correct
concentration of
GHG’s
 Temperature range of
10˚C to 20˚C
NASA | Image processing by R. Nunes
CO2
 Wide temperature
range of -135˚C to
30˚C
NASA | accessed via Wikipedia
NASA | accessed via Wikipedia
NASA | accessed via Wikipedia
Global Warming?
Why do we use the term “Global Warming”?
2000–2009 was the warmest decade on record worldwide