Abstract
Abstract. With recently improved instrumental accuracy, the change in the heat content of the oceans and the corresponding contribution to the change of the sea level can be determined from in situ measurements of temperature variation with depth. Nevertheless, it would be favourable if the same changes could be evaluated from just the sea surface temperatures because the past record could then be reconstructed and future scenarios explored. Using a single column model we show that the average change in the heat content of the oceans and the corresponding contribution to a global change in the sea level can be evaluated from the past sea surface temperatures. The calculation is based on the time-dependent diffusion equation with the known fixed average upwelling velocity and eddy diffusivity, as determined from the steady-state limit. In this limit, the model reduces to the 1966 Munk profile of the potential temperature variation as a function of depth. There are no adjustable parameters in the calculation and the results are in good agreement with the estimates obtained from the in situ data. The method allows us to obtain relevant timescales and average temperature profiles. The evaluation of the thermosteric sea level change is extended back to the beginning of accurate sea surface temperature records. The changes in sea surface temperature from 1880 until the present time are estimated to have produced a thermosteric sea level rise of 35 mm. Application to future IPCC scenarios gives results similar to the average prediction of more complex climate models.
Highlights
Accurate estimates of the change in ocean heat content have become available in the past two years (Domingues et al, 2008; Levitus et al, 2009) providing information on the major part of the global heat accumulation
The resulting global thermosteric sea level increase is an important component in the predictions of future climate change scenarios
We use here a time-dependent version of the Munk (1966) classic steady state analysis of potential temperature and salinity variation as a function of depth and show that it provides an accurate description of average global ocean heat content and thermosteric sea level change
Summary
Accurate estimates of the change in ocean heat content have become available in the past two years (Domingues et al, 2008; Levitus et al, 2009) providing information on the major part of the global heat accumulation. We use here a time-dependent version of the Munk (1966) classic steady state analysis of potential temperature and salinity variation as a function of depth and show that it provides an accurate description of average global ocean heat content and thermosteric sea level change. In the subsequent sections we show that using the advection-diffusion model with Munk’s average values for Az and W to calculate the average ocean heat content and sea level change produces accurate results. The applicability of the advection-diffusion model with Munk’s values for Az and W is extended to the calculation of average global temporal variations, including those occurring in the upper ocean. The solution is required, which uses sea surface temperatures as measured from 1880 to calculate the change in ocean heat content and thermosteric sea level. The report ends with a brief discussion, including the evaluation of the future steric sea level increase predicted from present-day temperatures and from standard IPCC scenarios
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