5.A.2 Heat Transports

Estimates of meridional heat transport (MHT) derived from the surface heat balance involve the integration of the zonally averaged balances in the longitudinal direction. This integration also implies the integration of uncertainties in the zonally averaged estimates. For instance, an uncertainty in zonally averaged estimates of ±10 W m^–2 results in an uncertainty of 0.5 × 10¹⁵ W in MHT in the Atlantic and nearly twice that value in the Pacific. Thus, all climatological estimates of MHT based on the surface heat balance have considerable uncertainties, and estimates of MHT variability are unlikely to be significant when derived from the surface heat balance.

In addition to the uncertainties in diagnostic computations of transports from vertical sections, estimates of MHT based on oceanic cross sections are largely influenced by sparse sampling of these sections during continuous time periods. As a result, there is no way to discriminate between the long-term signals and interannual variability using the estimates of MHT for individual years.