Brief IntroductionQuantifying Heat ContentConsequences of Temperature and Salinity ChangesConclusions (and Questions!)Oceanic Climate Change: Contributions of HeatContent, Temperature, and Salinity Trends toGlobal WarmingChristopher M. MirabitoInstitute for Computational Engineering and SciencesThe University of Texas at [email protected] 4, 2008Brief IntroductionQuantifying Heat ContentConsequences of Temperature and Salinity ChangesConclusions (and Questions!)Outline1Brief Introduction2Quantifying Heat Content3Consequences of Temperature and Salinity Changes4Conclusions (and Questions!)C. Mirabito Oceanic Climate ChangeBrief IntroductionQuantifying Heat ContentConsequences of Temperature and Salinity ChangesConclusions (and Questions!)The World OceanIt is the largest component of global climate system (recall that thecryosphere is the second largest), and has the largest heat capacityof any component [1, 6].It covers approximately 70% of the Earth’s surface.Half of the human population lives within 100 km of the coast;two-thirds within 400 km.It affects global precipitation, wind fields, jet streams, and stormtracks (including those of hurricanes and tropical cyclones) [1].Salinity affects the polar ice cap extent [1].C. Mirabito Oceanic Climate ChangeBrief IntroductionQuantifying Heat ContentConsequences of Temperature and Salinity ChangesConclusions (and Questions!)Causes of Oceanic Climate VariabilityNaturalNorth Atlantic Oscillation (NAO)Pacific Decadal Oscillation (PDO)El Ni˜no-Southern Oscillation (ENSO)Volcanic activityIce sheet meltingVery low frequency forcings which occur on time scales of severalhundred to a thousand years [4]AnthropogenicIncreases in CO2, CFCs, and other GHGs in the atmosphere affectthe ocean through surface layer mixing [1, 3, 4].C. Mirabito Oceanic Climate ChangeBrief IntroductionQuantifying Heat ContentConsequences of Temperature and Salinity ChangesConclusions (and Questions!)More about NAO and PDONAO: Bidecadal-scale air pressure oscillation inwhich high/low pressure centers over Icelandand the Azores vary in strength. NAO shiftedto a positive phase during the late 1970s.PDO: Quasi-bidecadal oscillation in Pacific watertemperatures. During a positive phase,eastern Pacific waters warm while westernwaters cool. PDO shifted to a positive phaseduring the late 1970s. PDO and NAO arehighly correlated [1].Image courtesy Wikipedia.C. Mirabito Oceanic Climate ChangeBrief IntroductionQuantifying Heat ContentConsequences of Temperature and Salinity ChangesConclusions (and Questions!)NAO at WorkFigure: Temperature difference (in◦C) at 1750 m for the North Atlantic for (a)1970–74 minus 1955–59 and (b) 1988–92 minus 1970–74. Figure takenfrom [2].Notice: During a negative NAO phase (e.g. before the late 1970s), muchof the North Atlantic warms. The opposite occurs during a positive NAOphase. Temperature changes are most pronounced in the North AtlanticSubpolar Gyre [1, 2].C. Mirabito Oceanic Climate ChangeBrief IntroductionQuantifying Heat ContentConsequences of Temperature and Salinity ChangesConclusions (and Questions!)Outline1Brief Introduction2Quantifying Heat Content3Consequences of Temperature and Salinity Changes4Conclusions (and Questions!)C. Mirabito Oceanic Climate ChangeBrief IntroductionQuantifying Heat ContentConsequences of Temperature and Salinity ChangesConclusions (and Questions!)Calculating Changes in Heat ContentThe total heat content Q (J) of a substance contained in some volume Vcan be expressed asQ =ZVρcpT dV ,where ρ is the density (kg · m−3) of the material, cpis the specific heatcapacity at constant pressure (J · kg−1·◦C−1), and T is the temperature(◦C).Since we wish to explore changes in heat content, we must calculate∆Q =ZVρcp∆T dV .C. Mirabito Oceanic Climate ChangeBrief IntroductionQuantifying Heat ContentConsequences of Temperature and Salinity ChangesConclusions (and Questions!)Estimate of ∆QAs a first-order estimate of ∆Q on a global scale from 1955 to 1996,takeρ = 1027 kg · m−3from [8],cp= 4184 J · kg−1·◦C−1from [7],∆T = 0.10◦C from [1]1, andV = 1.3703 × 1018m3from [8].Then∆Q ≈ 5.89 × 1023J,which has the same order of magnitude as the Levitus et al. [2] value of1.82 × 1023J.1This value is valid only from 1961 to 2003, but will be used here for simplicity.C. Mirabito Oceanic Climate ChangeBrief IntroductionQuantifying Heat ContentConsequences of Temperature and Salinity ChangesConclusions (and Questions!)Oceanic and Global Heat ContentClimate system Time period ∆Qcomponent of change (J)World Ocean 1955–1996 1.82 × 1023Continental glaciers 1955–1996 8.1 × 1021Global atmosphere 1955–1996 6.6 × 1021Antarctic sea ice extent 1950s–1970s 3.2 × 1021Mountain glaciers 1961–1997 1.1 × 1021NH sea ice extent 1978–1996 4.6 × 1019Arctic perennial sea ice volume 1950s–1990s 2.4 × 1019Table: A comparison of the contributions of various global climate systemcomponents to changes in global heat content. Table taken from [3] andslightly modified.Notice that the contribution from the World Ocean dominates that fromall other climate system components. This is not surprising sincecp,sea≈ 4.2cp,airand ρsea≈ 850ρair.C. Mirabito Oceanic Climate ChangeBrief IntroductionQuantifying Heat ContentConsequences of Temperature and Salinity ChangesConclusions (and Questions!)Spatial Variability of Temperature ChangesOur estimate of ∆Q was crude because spatial (and temporal) variabilityin ∆T and ρ (more on this later) was neglected. Temperatures (and thusheat content) change on gyre scales:Figure: Longitudinally-averaged temperature anomalies. Red areas indicatewarming; blue areas, cooling. Figure taken from [1].C. Mirabito Oceanic Climate ChangeBrief IntroductionQuantifying Heat ContentConsequences of Temperature and Salinity ChangesConclusions (and Questions!)Outline1Brief Introduction2Quantifying Heat Content3Consequences of Temperature and Salinity Changes4Conclusions (and Questions!)C. Mirabito Oceanic Climate ChangeBrief IntroductionQuantifying Heat ContentConsequences of Temperature and Salinity ChangesConclusions (and Questions!)Equation of StateThe following relationship between the density of seawater, temperature,salinity, and pressure holds:ρ(S, T , p) ≈ 1027 − 0.15(T − 10) + 0.78(S − 35) + 0.045.This is the equation of state (vastly simplified. . . the real equation ofstate contains 15 terms!) [8]. Notice that there is no
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