5.2.4 Air-Sea Fluxes and Meridional Transports

The global average changes in ocean heat content discussed above are driven by changes in the air-sea net energy flux (see Section 5.2.2.1). At regional scales, few estimates of heat flux changes have been possible. During the last 50 years, net heat fluxes from the ocean to the atmosphere demonstrate locally decreasing values (up to 1 W m^–2 yr^–1) over the southern flank of the Gulf Stream and positive trends (up to 0.5 W m^–2 yr^–1) in the Atlantic central subpolar regions (Gulev et al., 2006). At the global scale, the accuracy of the flux observations is insufficient to permit a direct assessment of changes in heat flux. Air-sea fluxes are discussed in Section 3.5.6.

Estimates of the climatological mean oceanic meridional heat transport derived from atmospheric observations (e.g., Trenberth and Caron, 2001) and from oceanographic cross sections (e.g., Ganachaud and Wunsch, 2003) are in fair agreement, despite considerable uncertainties (see Appendix 5.A.2). The ocean heat transport estimate derived from integration of climatological air-sea heat flux fields (e.g., Grist and Josey, 2003) is in good agreement with an independent oceanographic cross section at 32°S. Estimates of changes in the Atlantic meridional heat transport are discussed in Section 5.3.2.