Overview of the Climate System

Raymond NajjarPenn 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

PortlandsWinter 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 Infrared image

Minneapolis

Source: Nese and Grenci (2010)

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

solar radiation terrestrial radiation

Dominant Dominant greenhougreenhouse gasse gas

Increasing due to human activity

Sources: Nese & Grenci (2010), Kiehl & Trenberth (1997)

60%

26%

8%

6%

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) + 4T4

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 cycleBlack = 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

Source: www.pmel.noaa.gov/tao

Temperature section in the Equatorial Pacific

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

ReferencesDenman, 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

Source: Global Carbon Project, www.globalcarbonproject.org/carbonbudget

CO2 emissions from human activity (black) compared with the rate of increase in

atmospheric CO2 (blue)

Source: Global Carbon Project