Overview of the Climate System
Raymond Najjar
Penn State Department of Meteorology
• Definition of climate
• Climate system components
• Earth’s energy balance & the greenhouse effect
• Water and carbon cycles
• Internal variability vs. forced variability (ENSO example)
• Natural forcings vs. human-induced forcings
Climate of a region:
Statistical description of that
region’s weather
Portlands
Winter
temperature
probability
distributions
Portland, ME
(43.7°N)
Portland, OR
(45.5°N)
Source: NWS Climate
Prediction Center
Factors affecting a region’s climate
•
•
•
•
•
•
Latitude
Elevation
Proximity to ocean
Prevailing wind direction
Atmospheric composition
Land surface type
Visible image
Minneapolis
Source: Nese and Grenci (2010)
Infrared image
Minneapolis
Source: CLIVAR Program
Source: Wallace and Hobbs (2006). Based on Earth Radiation
Budget Experiment (ERBE), 1985-1986
Source: Wallace and Hobbs (2006). Based on Earth Radiation Budget Experiment
(ERBE), 1985-1986
Source: Wallace and Hobbs (2006). Based on Earth Radiation Budget Experiment
(ERBE), 1985-1986
Average = 30 W m-2
(warming)
Shortwave forcing average = 50 W m-2 (cooling)
Net effect: clouds cool 20 W m-2
Source: National Research Council (2008)
Global energy balance
Source: Kiehl & Trenberth (1997)
IR radiative forcing of the climate
IR radiation leaving the surface that is
absorbed in atmosphere
= 390 W m-2 – 235 W m-2 = 155 W m-2
Cloud IR forcing = 30 W m-2
Greenhouse gas forcing = 125 W m-2
Absorptivity of gases in the atmosphere
6%
8%
26%
60%
solar radiation
terrestrial radiation
Sources: Nese & Grenci (2010), Kiehl & Trenberth (1997)
Increasing
due to
human
activity
Dominant
greenhouse
gas
Contribution
to GHG
forcing
Calculation of surface temperature
without greenhouse forcing
Energy in = Energy out
Incoming solar = reflected solar + outgoing IR
1366 W m-2 = (0.30)(1366 W m-2) + 4sT4
T = 254 K = -19° C = 2° F
Greenhouse effect warms surface ~60° F
The global water cycle
Source: Trenberth et al. (2007)
The global carbon cycle
Black = preindustrial, Red = 1990s change
Denman et al. (2007)
CO2 role in greenhouse effect
• ~ 25% of clear-sky greenhouse effect
• ~ 20% of total greenhouse effect
• ~ 0.06% of the mass of the atmosphere
Forced vs. internal
variability of climate
• Forced: due to “external” processes;
e.g. solar, volcanic, & humans
• Internal: unforced variability; e.g.
ENSO, NAO, PDO, AMO, etc.
Current conditions in
the Tropical Pacific
Source: www.pmel.noaa.gov/tao
Temperature section in the Equatorial Pacific
Source: www.pmel.noaa.gov/tao
Source: www.pmel.noaa.gov/tao
Source: Nese and Grenci (2010)
ENSO variability over the past 60 years
MEI computed from surface winds, surface air and water
temperature, and cloud fraction
Source: www.esrl.noaa.gov/psd/enso/mei/
Natural vs. Human-induced
forcing of climate
• Natural: solar, earth-orbital, volcanic
• Human-induced: land use change,
greenhouse gases, aerosols, soot
Discussion
References
Denman, K.L., Brasseur, G., Chidthaisong, A., Ciais, P., Cox, P.M., Dickinson, R.E.,
Hauglustaine, D., Heinze, C., Holland, E., Jacob, D., Lohmann, U.,
Ramachandran, S., da Silva Dia, P.L., Wofsy, S.C., Zhang, X., 2007. Couplings
between changes in the climate system and biogeochemistry. In: S. Solomon, D.
Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, T. Tignor, H.L. Miller
(Editors), Climate Change 2007: The Physical Science Basis. Contribution of
Working Group I to the Fourth Assessment Report of the Intergovernmental
Panel on Climate Change. Cambridge University Press, Cambridge University
Press, Cambridge, United Kingdom and New York, NY, USA.
Kiehl, J.T., Trenberth, K.E., 1997. Earth's annual global mean energy budget. Bulletin
of the American Meteorological Society 78, 197-208.
National Research Council Committee on Scientific Accomplishments of Earth
Observations from Space, 2008. Earth Observations from Space: The First 50
Years of Scientific Achievements. The National Academies Press, Washington,
D. C., 142 pp.
Nese, J.M., Grenci, L.M., 2010. A World of Weather: Fundamentals of Meteorology,
Fifth Edition. Kendall Hunt Publishing Company, Dubuque, Iowa, 794 pp.
Trenberth, K.E., Smith, L., Qian, T., Dai, A., Fasullo, J., 2007. Estimates of the
Global Water Budget and Its Annual Cycle Using Observational and Model Data.
Journal of Hydrometeorology 8, 758-769.
Wallace, J.M., Hobbs, P.V., 2006. Atmospheric Science: An Introductory Survey,
Second Edition. Elsevier, Inc., Oxford, UK, 483 pp.
Extra slides
CO2 emissions from human activity (black) compared
with the rate of increase in atmospheric CO2 (blue)
Source: Global Carbon Project, www.globalcarbonproject.org/carbonbudget
Source: Global Carbon Project