Abstract
A straightforward mechanism based on properties of the moist adiabat is proposed to construe the observed latitudinal and longitudinal distribution of the anthropogenic forcing efficiency. Considering precipitation patterns at the planetary scale, idealized environmental adiabats leading to low-pressure systems are deduced. When the climate system responds to a small perturbation, which reflects radiative forcing that follows increasing anthropogenic emissions, the dry and moist adiabatic lapse rates move away from each other as the temperature of the moist adiabat at the altitude z = 0 increases. When the atmosphere becomes unstable, under the influence of the perturbation, a positive feedback loop occurs because of a transient change in the emission level height of outgoing longwave radiation in the saturated absorption bands of water vapor. During these periods of instability, the perturbation of the climate system is exerted with the concomitant warming of the surface temperature. In contrast, the return of the surface temperature to its initial value before the development of the cyclonic system is very slow because heat exchanges are mainly ruled by latent and sensible heat fluxes. Consequently, the mean surface temperature turns out to result from successive events with asymmetrical surface–atmosphere heat exchanges. The forcing efficiency differs according to whether atmospheric instability has a continental or oceanic origin. Hence the rendition of the latitudinal and longitudinal distribution of the observed surface temperature response to anthropogenic forcing, which specifies in detail the mechanisms involved in the various climate systems, including the Arctic amplification.
Highlights
Latitudinal responses of the Earth to the anthropogenic forcing, we have first to consider the evolution of the moist adiabat versus the temperature Tz=0 at the altitude z = 0
The way to make the atmosphere unstable is based on the properties of the moist adiabat as the air rises to the level of free convection
A straightforward mechanism was proposed, aiming at controlling the amplitude of the surface air temperature (SAT) response to anthropogenic forcing according to the various local climate systems
Summary
State of the Art. How increasing anthropogenic emissions lead to an increase of the greenhouse effect is often misunderstood and questioned. The increase in the surface air temperature (SAT) observed since the 1970s cannot be attributed to the natural variability of the climate and anthropogenic forcing is no longer a doubt. The SAT response to anthropogenic forcing is essentially governed by water vapor in the atmosphere and cloud feedbacks. Contrary to commonly accepted ideas, amplifying effects are not a consequence of the greenhouse effect resulting from the supposed increased atmospheric water vapor associated with the increased temperature. The regions least affected by anthropogenic warming are such that the increase in water vapor with temperature occurs in the free troposphere [1]
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