<p>This paper systematically analyses the natural convection heat transfer between the hydrosphere and the atmosphere, and mainly deals with spherical configurations that are a realistic representation of the two regions. Classical natural-convection concept in these areas is revisited through several recent developments, including convection at very high temperature differences, the effect of changing hydrosphere density, and the consideration of thermal and other physical properties in the atmosphere like thermal slip and porous media. The flow configuration, convection currents, and heat transfer rates are analysed using various dimensionless parameters such as Grashof number, Prandtl number, Darcy number and temperature variation parameters. The reviewed studies indicate that the thermal and velocity fields were greatly influenced by the density variations in the hydrosphere and by the thermal discontinuities and porosity in the atmosphere. By combining insights from numerical modeling and theoretical formulations, the present paper provides a logical basis for understanding the energies exchanged at the hydrosphere-atmosphere boundary and simultaneously points out the major research areas in the integrated transport processes, climate-sensitive modeling, and geophysical fluid dynamics. Notably, heat transfer initially increases with Darcy number, reaching a maximum at Da = 1.5, and decreases at higher values. This trend arises because low Da corresponds to restricted flow and limited heat transfer, intermediate Da enhances convective circulation, and high Da allows the flow to bypass thermal boundaries, slightly reducing overall heat transfer.</p>