Background and motivation

A warmer atmosphere can carry greater quantities of water vapour; approximately 6-7% more is carried per degree K of warming near Earth's surface, as determined by the Clausius-Clapeyron relation (O'Gorman et al., 2012). However, recent studies show that the hydrological sensitivity in the climate system, i.e. the long term precipitation response to equilibrium temperature change, is closer to 2-3% K-1. They conclude that the precipitation response to global warming cannot be explained by the availability of moisture alone (Andrews and Forster, 2010; Andrews et al., 2010; Frieler et al., 2011), but is constrained by the energy budget in the surface-atmosphere system (Allen and Ingram, 2002; O'Gorman et al., 2012).

The energy budget is altered by both natural and anthropogenic influences. Dependent on the physical properties of a climate forcing mechanism it causes either a fast response in precipitation, on a timescales of days to weeks, or a slower response on a timescale of years (Andrews et al., 2010; Ming et al., 2010; Frieler et al., 2011; Pendergrass and Hartmann, 2012). It has been shown that in several models at least in the global mean, fast atmospheric response correlates strongly with the atmospheric component of radiative forcing and the slower response with global surface temperature change (Andrews et al., 2010; Kvalevåg et al., 2013). A thorough investigation of differences in the effects of anthropogenic and natural drivers on precipitation will therefore lead to a reduction in uncertainties in global and regional predictions of both mean and extreme rainfall.

References

• Allen, M. R., and Ingram, W. J.: Constraints on future changes in climate and the hydrologic cycle, Nature, 419, 6903, 224, 10.1038/nature01092, 2002.
• Andrews, T., and Forster, P. M.: The transient response of global-mean precipitation to increasing carbon dioxide levels, Environmental Research Letters, 5, 2, 10.1088/1748-9326/5/2/025212, 2010.
• Andrews, T., Forster, P. M., Boucher, O., Bellouin, N., and Jones, A.: Precipitation, radiative forcing and global temperature change, Geophys. Res. Lett., 37, 10.1029/2010gl043991, 2010.
• Frieler, K., Meinshausen, M., von Deimling, T. S., Andrews, T., and Forster, P.: Changes in global-mean precipitation in response to warming, greenhouse gas forcing and black carbon, Geophys. Res. Lett., 38, 10.1029/2010gl045953, 2011.
• Kvalevåg, M. M., Samset, B. H., and Myhre, G.: Hydrological sensitivity to greenhouse gases and aerosols in a global climate model, Geophys. Res. Lett., 40, 7, 1432-1438, 10.1002/grl.50318, 2013.
• Ming, Y., Ramaswamy, V., and Persad, G.: Two opposing effects of absorbing aerosols on global-mean precipitation, Geophys. Res. Lett., 37, 10.1029/2010gl042895, 2010.
• O'Gorman, P. A., Allan, R. P., Byrne, M. P., and Previdi, M.: Energetic Constraints on Precipitation Under Climate Change, Surv. Geophys., 33, 3-4, 585-608, 10.1007/s10712-011-9159-6, 2012.
• Pendergrass, A. G., and Hartmann, D. L.: Global-mean precipitation and black carbon in AR4 simulations, Geophys. Res. Lett., 39, 10.1029/2011gl050067, 2012.