Abstract
Theory and model evidence indicate a higher global hydrological sensitivity for the same amount of surface warming to solar as to greenhouse gas (GHG) forcing, but regional patterns are highly uncertain due to their dependence on circulation and dynamics. We analyse a multi-model ensemble of idealized experiments and a set of simulations of the last millennium and we demonstrate similar global signatures and patterns of forced response in the tropical Pacific, of higher sensitivity for the solar forcing. In the idealized simulations, both solar and GHG forcing warm the equatorial Pacific, enhance precipitation in the central Pacific, and weaken and shift the Walker circulation eastward. Centennial variations in the solar forcing over the last millennium cause similar patterns of enhanced equatorial precipitation and slowdown of the Walker circulation in response to periods with stronger solar forcing. Similar forced patterns albeit of considerably weaker magnitude are identified for variations in GHG concentrations over the 20th century, with the lower sensitivity explained by fast atmospheric adjustments. These findings differ from previous studies that have typically suggested divergent responses in tropical precipitation and circulation between the solar and GHG forcings. We conclude that tropical Walker circulation and precipitation might be more susceptible to solar variability rather than GHG variations during the last-millennium, assuming comparable global mean surface temperature changes.
Highlights
In response to surface warming caused by a radiative forcing agent, global precipitation increases at an almost fixed rate of about 2.4%–2.6% degree−1 of global warming, independently of the nature of the agent (Andrews et al 2010, O’gorman et al 2012, Allan et al 2020)
Previous analysis of last millennium simulations have suggested that periods of high solar forcing increase sea surface temperature (SST) gradients in the equatorial Pacific Ocean and decrease rainfall, while increasing greenhouse gas (GHG) concentrations have the opposite effect (Mann et al 2009, Liu et al 2013)
Proxy reconstructions of surface temperature have suggested a cooling in the equatorial Pacific during the Medieval Climate Anomaly (MCA) that coincided with elevated solar activity, but model simulations do not provide support for such a La-Nina like response (Otto-Bliesner et al 2015)
Summary
In response to surface warming caused by a radiative forcing agent, global precipitation increases at an almost fixed rate of about 2.4%–2.6% degree−1 of global warming, independently of the nature of the agent (Andrews et al 2010, O’gorman et al 2012, Allan et al 2020) This temperature dependent increase in precipitation is commonly referred to as the slow component of the apparent (total) hydrological sensitivity, to differentiate from the rapid component, often of opposite sign, associated with near-instantaneous changes in the atmospheric energy budget and properties (Bala et al 2010, Myhre et al 2018). This mechanism is not effective in the case of increasing TSI, which is a driver that predominately warms the surface
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
