Review on Ocean Heat Content Variation and Ocean Warming OutlineIntroductionIntroductionTemporal Variability of Upper Ocean Heat Content Temporal Variability of Upper Ocean Heat Content Temporal Variability of Upper Ocean Heat Content Temporal Variability of Upper Ocean Heat Content GCM Model simulation resultsGCM Model simulation resultsPCM Model simulation resultsPCM Model simulation resultsPCM Model simulation resultsInterannual variability of upper ocean heat contentInterannual variability of upper ocean heat contentInterannual variability of upper ocean heat contentInterannual variability of upper ocean heat contentInterannual variability of upper ocean heat contentInterannual variability of upper ocean heat contentLarge-scale trends in salinityLarge-scale trends in salinitySummaryReview on Ocean Heat Content Variation and Ocean WarmingLei Huang11/25/2008Outline¾ Introduction¾ Temporal and Spatial Variability ¾ GCM Model simulation results ¾ PCM Model simulation results ¾ Interannual variability ¾ Large-scale trends in salinityIntroductionGlobal mean surface temperature anomaly relative to 1961–1990 Mean surface temperature anomalies during the period 1995 to 2004 with respect to the average temperatures from 1940 to 1980¾Understanding how ocean warming and the resulting thermal expansion contributes to rising sea levels is critically important to understanding climate change, and forecasting future temperature rises.¾Scientists found that from 1961 to 2003, ocean temperatures to a depth of 700 metres, contributed to an average rise in sea levels of 0.52 millimetre-per-year compared to a 0.32 millimetre rise reported by the IPCC 2007.¾“Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.”-----IPCC 2007IntroductionTemporal Variability of Upper Ocean Heat Content• The anomaly fields for the Atlantic and Indian oceans show a positive correlation.• In each basin before the mid-1970s, temperatures relatively cool, whereas after the mid-1970s these oceans are in a warm state.• Both Pacific Ocean basins exhibit quasi-bidecadal changes in upper ocean heat content, with the two basins positively correlated. • A decadal-scale oscillation in North Pacific sea surface temperature (Pacific Decadal Oscillation) has been identified.-- Levitus et al., 2000Temporal Variability of Upper Ocean Heat Content-- Levitus et al., 2000• Consistent warming signal in each ocean basin, not monotonic. • North and south Pacific and Indian oceans are positively correlated, suggesting the same basin-scale forcings. • The temporal variability of the South Atlantic differs significantly from the North Atlantic, due to the deep convective processes that occur in the North Atlantic.• The delayed warming of the Indian Ocean may be due to the sparsity of data in the Indian Ocean before 1960.Temporal Variability of Upper Ocean Heat ContentTemperature difference (C) at 1750-m depth of the North Atlantic for (A) 1970-74 minus 1955-59 and (B) 1988-92 minus 1970-74.--Levitus et al., 2000Temporal Variability of Upper Ocean Heat ContentHeat storage for the North Atlantic for 1988-92 minus 1970-74. (A) Integral between the surface and 300-m depth; (B) integral between the surface and 3000-m depth.--Levitus et al., 2000¾ coupled ocean-atmosphere-ice model ¾ global in domain and consists of GCMs of the atmosphere and ocean¾ Atmosphere: 3.75°longitude by 2.25°latitude, with 14 vertical levels.¾ Ocean: 1.875°longitude by 2.25°latitude, with 18 vertical levels. ¾ Over oceanic regions, a thermodynamic sea ice model is used that includes the advection of ice by surface ocean currents.GCM Model simulation resultsGCM Model simulation results-- Levitus et al., 2001Time series of various components of the observed and simulated global heat content.Two ensembles of integrations: the first ensemble includes the radiativeeffects of the observed temporal variations in GHGs, sulfate aerosols, solar irradiance, and volcanic aerosols over the past century; the second ensemble omits the radiative effects of changes in solar irradiance and volcanic aerosols.First ensemble, linear trend, excellent agreement with the observed estimate Second ensemble, 70% larger than in first one or than the observed estimate.The difference is primarily due to the radiative effects of volcanic activity.¾ Parallel Climate Model (PCM): a state-of-the-art global climate model. ¾ Using no flux-correction scheme, forced by observed and estimated concentrations of greenhouse gases and the direct effect of sulfate aerosols on the atmosphere.PCM Model simulation resultsPCM Model simulation results-- Barnett et al., 2001Decadal values of anomalous heat content in various ocean basins.Decadal temperature anomalies (°C) in various ocean basins since 1870 from the PCMPCM Model simulation results-- Barnett et al., 2001Modeled and observed temporal and vertical changes in the temperature in the upper 2000 m of the data-rich North Pacific and North Atlantic Oceans. Detection and attribution diagramInterannual variability of upper ocean heat content-- Willis et al., 2004Globally averaged heat content variability.• A considerable warming trend• The 10-year heat increase from mid-1993 to mid-2003 implied an average warming rate of 0.86 ±0.12 watts per square meter of ocean• A significant amount of interannual variability is present in the time series of the difference field-- Willis et al., 2004Maps of 10-year change in heat content.(a) Difference estimate (combined altimeter and in situ data); (b) Estimate from in situ data alone. The curves on the right-hand side show the zonal integral of the maps in watts per meter of latitude; (c) Number of in situ profile per 10° box.Interannual variability of upper ocean heat content-- Willis et al., 2004Globally averaged heat storage variability.¾ A rapid warming during the onset of the 1997–1998 El Nino, followed by a slight cooling in the latter part of 1998.¾ Significant inter-annual variability.¾ An error bar of 0.6 W/m2 for the time series of the difference estimate.-- Willis et al., 2004Maps of heat storage variability. Each map is a 1-year average centered on the year shown.Interannual variability of upper ocean heat content-- Willis et al., 20049 Time-latitude plot of zonally integrated heat content.9 The most prominent feature is the