Are Changes in Global Precipitation Constrained by the Tropospheric Energy Budget?

Abstract

A tropospheric energy budget argument is used to analyze twentieth-century precipitation changes. It is found that global and ocean-mean general circulation model (GCM) precipitation changes can be understood as being due to the competing direct and surface-temperature-dependent effects of external climate forcings. In agreement with previous work, precipitation is found to respond more strongly to anthropogenic and volcanic sulfate aerosol and solar forcing than to greenhouse gas and black carbon aerosol forcing per unit temperature. This is due to the significant direct effects of greenhouse gas and black carbon forcing. Given that the relative importance of different forcings may change in the twenty-first century, the ratio of global precipitation change to global temperature change may be quite different. Differences in GCM twentieth-and twenty-first-century values are tractable via the energy budget framework in some, but not all, models. Changes in land-mean precipitation, on the other hand, cannot be understood at all with the method used here, even if land-ocean heat transfer is considered. In conclusion, the tropospheric energy budget is a useful concept for understanding the precipitation response to different forcings but it does not fully explain precipitation changes even in the global mean.

Cloud Adjustment and its Role in CO2 Radiative Forcing and Climate Sensitivity: A Review

“…It is changes in condensational heating and associated precipitation/surface evaporation that play this role (e.g., Mitchell et al 1987;Allen and Ingram 2002;Lambert and Allen 2009). Global mean precipitation initially decreases following an increase in CO 2 through rapid tropospheric adjustment processes, then increases on a multi-annual timescale associated with changes in global surface temperature.…”

“…For example, the condensational heating associated with precipitation provides a link between the hydrological cycle and radiative processes such as cloud feedback (Stephens 2005;Stephens and Ellis 2008). An advantage of this approach is that precipitation adjustments, particularly in response to greenhouse gases or black carbon aerosol, are subject to energetic constraints and provide a more robust signal across climate models than cloud adjustments do, and therefore are potentially easier to observe in transient forcing scenarios (e.g., Lambert and Allen 2009;Frieler et al 2011). However, there is still substantial disagreement on recent precipitation trends across datasets (e.g., Arkin et al 2010), presenting a considerable challenge if attempting to tease out adjustment processes.…”

The sensitivity of the modeled energy budget and hydrological cycle to CO<sub>2</sub> and solar forcing

“…on the different forcing agents (Shiogama et al, 2010a;Lambert and Allen, 2009). It is widely accepted that the global mean precipitation change per unit temperature change is more sensitive to changes in aerosols or solar radiation than to changes in CO 2 concentrations (Allen and Ingram, 2002;Gillett et al, 2004;Andrews et al, 2009;Liepert and Previdi, 2009;Bala et al, 2010).…”

Causes of Robust Seasonal Land Precipitation Changes*

“…Global and regional precipitation changes may be influenced by a complex range of factors including the direct response to greenhouse gas forcing and to the warming of the atmosphere (Allen and Ingram 2002;Lambert and Allen 2009), changes in atmospheric circulation (e.g., Ineson and Scaife 2009; Kenyon and Hegerl 2010), sea surface temperature changes (e.g., Hoerling et al 2012;Yoshioka et al 2007;Lyon and DeWitt 2012;Hoerling et al 2012), and regional changes in vegetation (e.g., Wang et al 2004) and stratospheric aerosols (e.g., Gillett et al 2004).…”

“…Thus, areas that export moisture get drier and areas that import water get wetter . However, the increase in global precipitation is constrained by tropospheric radiative cooling with precipitation increasing at a slower rate than column water vapor (Allen and Ingram 2002;Lambert and Allen 2009). There must therefore be a corresponding decrease in the convective mass flux, implying weakening atmospheric circulation in the tropics, where most moist convection occurs (Vecchi et al 2006;Lu et al 2007).…”