A simple explanation for the sensitivity of the hydrologic cycle to surface temperature and solar radiation and its implications for global climate change Max-Planck-Institut für Biogeochemie, Jena, Germany
05 Dec 2013
Received: 30 Jul 2013 – Published in Earth Syst. Dynam. Discuss.: 14 Aug 2013 Abstract. The global hydrologic cycle is likely to increase in strength with global
warming, although some studies indicate that warming due to solar absorption
may result in a different sensitivity than warming due to an elevated
greenhouse effect. Here we show that these sensitivities of the hydrologic
cycle can be derived analytically from an extremely simple surface energy
balance model that is constrained by the assumption that vertical convective
exchange within the atmosphere operates at the thermodynamic limit of maximum
power. Using current climatic mean conditions, this model predicts a
sensitivity of the hydrologic cycle of 2.2% K−1 to
greenhouse-induced surface warming which is the sensitivity reported from
climate models. The sensitivity to solar-induced warming includes an
additional term, which increases the total sensitivity to 3.2% K−1.
These sensitivities are explained by shifts in the turbulent fluxes in the
case of greenhouse-induced warming, which is proportional to the change in
slope of the saturation vapor pressure, and in terms of an additional
increase in turbulent fluxes in the case of solar radiation-induced warming.
We illustrate an implication of this explanation for geoengineering, which
aims to undo surface temperature differences by solar radiation management.
Our results show that when such an intervention compensates surface warming,
it cannot simultaneously compensate the changes in hydrologic cycling because
of the differences in sensitivities for solar vs. greenhouse-induced surface
warming. We conclude that the sensitivity of the hydrologic cycle to surface
temperature can be understood and predicted with very simple physical
considerations but this needs to reflect on the different roles that solar and
terrestrial radiation play in forcing the hydrologic cycle.
Revised: 15 Oct 2013 – Accepted: 25 Oct 2013 – Published: 05 Dec 2013
Citation: Kleidon, A. and Renner, M.: A simple explanation for the sensitivity of the hydrologic cycle to surface temperature and solar radiation and its implications for global climate change, Earth Syst. Dynam., 4, 455-465, doi:10.5194/esd-4-455-2013, 2013.