Extended Data Fig. 2: Variations in the wet Bowen ratio (β_w) from wet to the hypothetically driest conditions.

a, Illustration of the difference in \({\beta }_{w}\) when an ocean grid cell were artificially dried up completely. The grey curve shows the saturation vapor pressure (\({e}^{* }/\gamma\)) as a function of temperature (\(T\)), while the two dashed lines represent air and surface isenthapic processes with constant enthalpy, \(T+e/\gamma\), from wet to the driest conditions. Temperature and vapor pressure for the air and surface are shown in blue for the wet state, pink for the dry state, and purple for the driest state. b, Illustration of changes in \({\beta }_{w}\) when surface and air temperatures change proportionally from wet to the driest conditions for the ocean grid cell. The x-axis refers to the mean surface and air temperature. The blue line shows \({\beta }_{{pt}}\) inferred from the Priestley-Taylor equation (PETpt) for the same ocean grid cell. c-d, Frequency distribution of the sensitivities of \({\beta }_{w}\) and \({\beta }_{{pt}}\) to mean temperature, that is, the ratio of the differences in \({\beta }_{w}\) and \({\beta }_{{pt}}\) over the difference in mean temperature (\(d{\beta }_{w}/{dT}\) and \(d{\beta }_{{pt}}/{dT}\)) between wet and the driest conditions, for ocean grid cells in 2020 and 2100, based on 32 CMIP6 models. Mean sensitivities of \({\beta }_{w}\) and \({\beta }_{{pt}}\) across all grid cells are shown in parentheses.