Abstract
Abstract. Some large-scale components of the Earth's climate system have been identified as policy-relevant “tipping elements”, meaning that anthropogenic forcing and perturbations may push them across a tipping point threshold, with potential global scale impact on ecosystems and concomitant environmental and social phenomena. A pronounced change in the amplitude and/or frequency of the El Niño–Southern Oscillation (ENSO) is among such tipping elements. Here, we use the Planet Simulator (PlaSim), an Earth system model of intermediate complexity, to investigate the potential impact on global climate and terrestrial ecosystems of shifting the current dynamics of the ENSO into a permanent El Niño. When forced with sea surface temperature (SST) derived from observations, the PlaSim model yields a realistic representation of large-scale climatological patterns, including realistic estimates of the global energy and water balances, and gross primary productivity (GPP). In a permanent El Niño state, we found significant differences in the global distribution of water and energy fluxes, and associated impacts on GPP, indicating that vegetation production decreases in the tropics, whereas it increases in temperate regions. We identify regions in which these El Niño-induced changes are consistent with potential state transitions in global terrestrial ecosystems, including potential greening of western North America, dieback of the Amazon rainforest, and further aridification of south-eastern Africa and Australia.
Highlights
Earth’s current climatology can be considered a steady state of a non-equilibrium system (Kleidon, 2010) in which constant influx of solar radiation and internal feedback mechanisms stall equilibrium, so that properties of the climate system can remain relatively close to mean values
Differences between Planet Simulator (PlaSim) and observations indicate that the model overestimates the outgoing solar radiation at TOA, as a result of more solar radiation being reflected both at the surface and atmosphere, and less solar radiation being absorbed by the atmosphere
The surface energy balance in the model shows realistic estimates of thermal, latent heat (LH), and sensible heat (SH) fluxes, with a slightly overestimated Bowen ratio (SH / LH) of 0.23 as compared to 0.21 in both ERA-Interim and TFM11. These biases in the surface fluxes are likely to be related to prescribed values of aerodynamic roughness length (Yang et al, 2002), which has been related to ERA-Interim biases (Zhou and Wang, 2016)
Summary
Earth’s current climatology can be considered a steady state of a non-equilibrium system (Kleidon, 2010) in which constant influx of solar radiation and internal feedback mechanisms stall equilibrium, so that properties of the climate system can remain relatively close to mean values. It is becoming increasingly clear that the Earth’s climate system as a whole, as well as some of its large-scale components or subsystems, have tipping points (i.e. critical thresholds in forcing and/or a feature of the system) at which the system shifts from one state (e.g. current climate) to another (e.g. future climate) (Lenton et al, 2008; Scheffer et al, 2009). A tipping element is a large-scale component of the Earth system that may pass over a tipping point with the potential to alter global climate. A pronounced change in the amplitude and/or frequency of the El Niño– Southern Oscillation (ENSO), including its shift into a permanent El Niño state, is among the policy-relevant tipping elements identified by Lenton et al (2008). Greenhouse warming in climate projections can lead to more frequent El Niño events, because it diminishes temperature gradients in the eastern equatorial Pacific Ocean, which facilitate the changes in convection zones that are observed during this phenomenon (Cai et al, 2014; Latif et al, 2015)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
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 call
