Ocean variability and its influence on the detectability of greenhouse warming signals

Technical Report · Sat Jan 01 04:00:00 EST 1994

OSTI ID:140925

Santer, B D ^[1]; Mikolajewicz, U; Brueggemann, W; Hasselmann, K; Hoeck, H; Maier-Reimer, E ^[2]; Cubasch, U ^[3]; Wigley, T M.L. ^[4]

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1. Lawrence Livermore National Lab., CA (United States)
2. Max-Planck-Institut fuer Meteorologie, Hamburg (Germany)
3. Deutsches Klimarechenzentrum, Hamburg (Germany)
4. UCAR Office for Interdisciplinary Earth Sciences, Boulder, CO (United States)

Recent investigations have considered whether it is possible to achieve early detection of greenhouse-gas-induced climate change by observing changes in ocean variables. In this study, we use model data to assess some of the uncertainties involved in estimating when we could expect to detect ocean greenhouse warming signals. We distinguish between detection periods and detection times. As defined here, detection period is the length of a climate time series which must be available in order to detect a given linear trend in the presence of the natural climate variability. Detection period is defined in model years and is independent of reference time and the real time evolution of the signal. Detection time is computed for an actual time-evolving signal from a greenhouse warning experiment and depends on the experiment`s start date. Two sources of uncertainty are considered - those associated with the level of natural variability or noise, and those associated with the time-evolving signals. We analyze the ocean signal and noise for spatially-averaged ocean circulation indices such as ice volume, heat and fresh water fluxes, rate of deep water formation, salinity, temperature, and transport of mass. The signals for these quantities are taken from recent time-dependent greenhouse warming experiments performed by the Hamburg group with a coupled ocean-atmosphere General Circulation Model. The natural variability noise is derived from a 300-year control run performed with the same coupled atmosphere-ocean model and from two long (> 3,000 year) stochastic forcing experiments in which an uncoupled ocean model was forced by white-noise surface flux variations. In the first experiment the stochastic forcing was restricted to the fresh water fluxes, while in the second experiment the ocean model was additionally forced by variations in wind stress and heat fluxes. The mean states and ocean variability are very different in the three natural variability integrations.

• Research Organization: Lawrence Livermore National Lab., CA (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 140925
• Report Number(s): UCRL-ID--115329; PCMDI--14; ON: DE94008670
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
AIR-WATER INTERACTIONS
DETECTION
GENERAL CIRCULATION MODELS
GREENHOUSE EFFECT
SEAS