Recent Climate, Energy Balance
and the Greenhouse Effect
David B. Reusch
Penn State/New Mexico Tech
dreusch@ees.nmt.edu
CVEEN 7920/Geol 571
~4 x 1026 W
W = watts = power = energy/sec
~4 x 1026 W
W = watts = power = energy/sec
~4 x 1026 W
W = watts = power = energy/sec
W = watts = power = energy/sec
Basic Balance
 342 W/m2 of shortwave radiation input
from the Sun is balanced by…
 Earth outputs totaling 342 W/m2 of
 Reflected/scattered
shortwave
 Absorbed/re-emitted longwave
 So what temperature is that?
Earth’s Average Temperature
 An input of 342 W/m2 translates to a
mean surface temperature of -18 °C
 We know that TA is actually 15 °C so
what’s missing?
 The short answer: an atmosphere which
provides the natural greenhouse effect
E=
4
T
~4 x 1026 W
W = watts = power = energy/sec
Natural Greenhouse Effect
What Wavelength?
 Sun ~6000 K, Earth ~288 K
 Dominant Wavelength
 Inversely
related to temperature (Wien’s)
 Hotter -> shorter wavelength
 Sun @ 0.48 m (480 nm; visible)
 Earth @ 10 m (infrared or IR)
 Radiation emitted over a range of
wavelengths
2897
6

*10 m
T
Solar Peak
Terrestrial
Peak
Note: shape of
Earth’s spectrum.
It’s modified by the
atmosphere!
What Happens To Insolation?




Reflection
Scattering
Absorption
Transmission
Reflection
 Change in direction of a wave on
encountering an interface
 Atmosphere, clouds and surface
 Measured by albedo
Reflection (and albedo)
a = 35-75%
a5-85%
Scattering
 Random redirection of light by the
atmosphere
 Wavelength and particle concentration
dependence
 Rayleigh (blue skies) and Mie (white
clouds) are main processes
Scattering
Absorption
 Energy taken up by object (photon is
absorbed and destroyed)
 Anything absorbed must be re-emitted
to maintain equilibrium
 At Earth temperatures, this converts
shortwave into longwave when energy
is re-emitted
Absorption
Absorption
 Atmosphere absorbs selectively (only
some wavelengths)
 Mostly transparent in visible range
 Broad range of longwave absorbed by
various greenhouse gases
 Stratospheric O2 & O3 absorb UV
http://wxpaos09.colorado.edu/radiation/background.html
UV & Visible
IR or longwave
http://www.atmos.washington.edu/~dennis/Energy_Flow.gif
Shortwave
31% reflected directly
49% absorbed by surface
20% absorbed by atmosphere
http://www.atmos.washington.edu/~dennis/Energy_Flow.gif
390 W/m2 is energy from
a body at 15 °C
Longwave
http://www.atmos.washington.edu/~dennis/Energy_Flow.gif
Longwave
http://www.atmos.washington.edu/~dennis/Energy_Flow.gif
Longwave
http://www.atmos.washington.edu/~dennis/Energy_Flow.gif
Balance incoming
Outgoing Longwave Radiation
http://www.cdc.noaa.gov/
Additional complexity
 Earth is a rough sphere
 Slope,
aspect
 Latitude
 Time/space varying albedo (reflectivity)
 Vegetation,
snow/ice, soils, moisture
 Human land use change
 Atmospheric composition/structure, clouds
 Ocean, ice
Composition: Stable
 Main components of dry atmosphere
are pretty stable (~99%)
 78% N2, 21% O2
 Long-term (geologic) rise in oxygen
 Changes in stable isotope ratios
Composition: Variable
 Minor by volume (< 1%) but major by
climate effect in many cases (GHGs)
 Reactive (S, N, Cl cycles)
 Non-reactive (CO2, CFCs)
 Water vapor (up to 4% by volume)
 Particulates (aerosols)
 Variation exists over many time and
space scales
Greenhouse gases
 Certain naturally occurring trace gases
change the atmosphere’s energy balance
 Carbon
dioxide (CO2), Methane (CH4)
 Water vapor and others…
 Contribution to warming varies
 By
concentration
 By “radiative efficiency”
 By lifetime in the atmosphere
Leading Greenhouse Gases
Gas
Concentration
Carbon Dioxide (CO2)
380 ppm
Methane (CH4)
1700 ppb
Nitrous oxide (N2O)
Ozone (O3)
 Mexicoare
~one
million
Note: concentrations
approximate!

500 ppb
70 ppb
people
India ~one billion people
http://www.ipcc.ch/present/graphics/2001syr/large/02.01.jpg
http://www.ipcc.ch -- Climate Change 2007: Summary for Policymakers
Seasonal Cycle
in NH Biota
Anthropogenic
Influence
33
Solar Base = 342 W m-2
Recent Change
and Variability
Recent Climate Variations:
Surface Air Temperature
http://www.ipcc.ch -- Climate Change 2007: The Physical Science Basis (Chapter 3)
Fi gur e 3. 1
Ranked Global Temperatures
Tied
http://www.ncdc.noaa.gov/sotc
Spatial Changes in Temperature
http://www.ipcc.ch -- Climate Change 2007: The Physical Science Basis (Chapter 3)
http://nsidc.org/data/glacier_photo/repeat_photography.html
Muir Glacier, Alaska, August 13, 1941, photo by W.O. Field
http://nsidc.org/data/glacier_photo/repeat_photography.html
Muir Glacier, Alaska, August 31, 2004, photo by B.F. Molnia, USGS
Grinnell Glacier 1938-2005
Glacier National Park
1938
1981
http://en.wikipedia.org/wiki/Retreat_of_glaciers_since_1850
2005
Spatial Changes in Precipitation
http://www.ipcc.ch -- Climate Change 2007: The Physical Science Basis (Chapter 3)
Recent Climate Variations: Sea Level
http://www.ipcc.ch -- Climate Change 2007: The Physical Science Basis (Chapter 5)
Arctic Sea Ice Trends
http://nsidc.org/sotc/sea_ice.html
Sept 2007 All-time Minimum
http://nsidc.org/news/press/2007_seaiceminimum/20071001_pressrelease.html
500 Million Years of Change
http://en.wikipedia.org/wiki/User:Dragons_flight/Images
500 Million Years of Change
http://en.wikipedia.org/wiki/User:Dragons_flight/Images
500 Million Years of Change
http://en.wikipedia.org/wiki/User:Dragons_flight/Images
Today is Different
 Rates of change not seen in geologic
record
 World did not have nearly 7 billion
people