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National Aeronautics and Space Administration
The Greenhouse Effect
www.nasa.gov
Dr. Lin H. Chambers, NASA Langley Research Center
Hampton, Virginia
NASA Climate Day Workshop, Oct. 2011
National Aeronautics and Space Administration 2
The Electromagnetic Spectrum
http://mynasadata.larc.nasa.gov/ElectroMag.html
National Aeronautics and Space Administration 3
The Blackbody Spectrum – The Sun
http://phet.colorado.edu/simulations/sims.php?sim=Blackbody_Spectrum
National Aeronautics and Space Administration 4
The Blackbody Spectrum – Light Bulb
http://phet.colorado.edu/simulations/sims.php?sim=Blackbody_Spectrum
National Aeronautics and Space Administration 5
The Blackbody Spectrum – Light Bulb
http://phet.colorado.edu/simulations/sims.php?sim=Blackbody_Spectrum
Note Scale Change!
National Aeronautics and Space Administration 6
The Electromagnetic Spectrum
http://radiojove.gsfc.nasa.gov/education/educ/radio/tran-rec/exerc/iono.htm
Peak of Earth emission ~10 mm = 104 nm
National Aeronautics and Space Administration 7
The Earth’s Energy Budget
http://mynasadata.larc.nasa.gov/preview_lesson.php?&passid=63
National Aeronautics and Space Administration
At the top of the atmosphere:
+ Sunlight In – Sunlight reflected from clouds/atmosphere– Sunlight reflected from surface – IR emission 0
8
Balancing the Budget - I
http://mynasadata.larc.nasa.gov/preview_lesson.php?&passid=44
Equilibrium
Temperature: -18 °C
National Aeronautics and Space Administration 9
Balancing the Budget - II
At the Earth’s surface:
+ Sunlight absorbed – IR emission+ IR back radiation (greenhouse effect)– Thermals – Evapotranspiration 0
http://mynasadata.larc.nasa.gov/preview_lesson.php?&passid=63http://mynasadata.larc.nasa.gov/preview_lesson.php?&passid=67
Equilibrium
Temperature: 15 °C
National Aeronautics and Space Administration 10
The Enhanced Greenhouse Effect
Starting point:
Earth at equilibrium with net energy input from the Sun.
Average surface temperature 288 K (15 C; ~59 F)
National Aeronautics and Space Administration 11
The Enhanced Greenhouse Effect
The experiment:
Instantaneously double CO2 in concentration in atmosphere
Average energy emitted by Earth drops 4 W/m2 (236 vs 240)
National Aeronautics and Space Administration 12
The Enhanced Greenhouse Effect
Response:
All other things being equal, simple blackbody theory says:
Average surface temperature rises 1.2 K (or C; ~2.1 F)
Energy back in balance
National Aeronautics and Space Administration 13
The Enhanced Greenhouse Effect
Feedbacks:
In Earth system, other processes kick in (water vapor feedback, cloud feedback, ice-albedo feedback, etc).
Net effect: Average surface temperature estimated to rise 2-4.5 K (~3.6 to 8 F)
National Aeronautics and Space Administration 14
Forcings on the Greenhouse
http://ipcc.ch/publications_and_data/ar4/wg1/en/figure-spm-2.html
National Aeronautics and Space Administration
• This figure depicts mostly positive and long-lived forcing agents from 1950 through 2004. The positive forcing agents are items that cause the atmosphere to show an overall warming trend because they trap additional energy in the atmosphere (enhanced greenhouse effect). The greenhouse gasses shown in the figure (carbon dioxide - CO2, methane - CH4, halocarbons, nitrous oxide - N2O and stratospheric + tropospheric ozone - O3) have increased in the atmosphere mostly due to human activities. A natural change from variations in the Sun’s output is shown along the bottom of the graph This figure shows the cumulative effect of small changes. The additional heat trapped each year continues to add up to a warmer Earth.
Physics of Our Atmosphere 15
Energy Balance analysis
http://science-edu.larc.nasa.gov/energy_budget/
National Aeronautics and Space Administration
• Knowing how much additional heat is trapped (because we know how much of these gasses were emitted) the question becomes: where did the energy go? This figure partitions the added energy shown above based on observed changes. So far, a small amount of the energy has gone into warming the ocean – the part of the Earth that stores the most energy. Some has escaped Earth in the form of increased IR emission because of warmer temperatures. Some was reflected to space by aerosols (mostly volcanic in origin) in the stratosphere. The remainder (white band) is inferred to have been rejected due to aerosols (mostly pollution) in the troposphere, and other effects such as a changing reflection of the land surface due to deforestation, for example.
Physics of Our Atmosphere 16
Where did the Energy Go?
http://science-edu.larc.nasa.gov/energy_budget/
National Aeronautics and Space Administration 17
Interactive Applet
http://profhorn.meteor.wisc.edu/wxwise/climate/makeplanet.html
National Aeronautics and Space Administration MY NASA DATA: A REASoN Project 18