Theme Session 1.1
Past and future variability and change in ocean climate
Title: Observed ocean climate changes: a review based on the IPCC AR4 and subsequent works
Lynne D. Talley
Scripps Institution of Oceanography, UCSD, La Jolla, CA, USA
Changes in ocean temperature, salinity, oxygen and circulation over the past several decades, and their relation to changes in atmospheric forcing, were thoroughly synthesized in the Intergovernmental Panel on Climate Change's Fourth Assessment Report, published in February 2007. The conclusions of that synthesis were based on peer-reviewed materials published prior to 2006. Primary conclusions are the following, based on these published materials. From 1955 to 2003, the oceans were warming, with 2/3 of the heating in the upper 700 m. The warming was not uniform; the subpolar North Atlantic and North Pacific and tropical Pacific warm pool were cooling, but not enough to offset the global warming trend. Global mean sea level was rising, and the rate was increasing; like temperature, sea level changes also exhibited large regional variations. Salinity is changing regionally, with higher latitudes and the Pacific freshening, while lower latitudes and the Atlantic and Indian are becoming saltier, roughly consistent with a stronger atmospheric hydrological cycle, which is consistent with a warmer atmosphere and hence climate change. Oxygen had been decreasing in the pycnocline in subpolar regions, consistent with decreased ventilation at the base of the climatological pyncocline. On the other hand, circulation trends were not robust. The Atlantic meridional overturning circulation was of particular interest, but variability was dominated by interannual and decadal change; any trends were too weak in comparison to be apparent. The work reviewed in the IPCC was principally based on research ship-based observations and local experiments; climatologies were constructed by simple processing of these regional data sets. Many of the newer results that are brought together here are also based on direct regional observations. Newer products also include the growing body of distributed subsurface float profiles (Argo) as well as data assimilation for the Topex/Poseidon altimetry period. Ocean and climate models are also providing important information for interpreting the observed changes.