A PDRMIP Multimodel Study on the Impacts of Regional Aerosol Forcings on Global and Regional Precipitation

Abstract

Atmospheric aerosols such as sulfate and black carbon (BC) generate inhomogeneous radiative forcing and can affect precipitation in distinct ways compared to greenhouse gases (GHGs). Their regional effects on the atmospheric energy budget and circulation can be important for understanding and predicting global and regional precipitation changes, which act on top of the background GHG-induced hydrological changes. Under the framework of the Precipitation Driver Response Model Intercomparison Project (PDRMIP), multiple models were used for the first time to simulate the influence of regional (Asian and European) sulfate and BC forcing on global and regional precipitation. The results show that, as in the case of global aerosol forcing, the global fast precipitation response to regional aerosol forcing scales with global atmospheric absorption, and the slow precipitation response scales with global surface temperature response. Asian sulfate aerosols appear to be a stronger driver of global temperature and precipitation change compared to European aerosols, but when the responses are normalized by unit radiative forcing or by aerosol burden change, the picture reverses, with European aerosols being more efficient in driving global change. The global apparent hydrological sensitivities of these regional forcing experiments are again consistent with those for corresponding global aerosol forcings found in the literature. However, the regional responses and regional apparent hydrological sensitivities do not align with the corresponding global values. Through a holistic approach involving analysis of the energy budget combined with exploring changes in atmospheric dynamics, we provide a framework for explaining the global and regional precipitation responses to regional aerosol forcing.

Dynamical response of Mediterranean precipitation to greenhouse gases and aerosols

“…In other words, the precipitation trends during the past 110 years in the Mediterranean are likely to be only weakly sensitive to scattering aerosols that were not modeled (e.g., organic carbon, nitrate) or the uncertainties in aerosol negative forcing (probably not even for indirect forcing, as they were included in sulfate simulations for most models). The small sensitivity of SO 4 is likely due to compensation between local and remote effects (Liu et al, 2018). Combined with its small ERF, the role of SO 4 appears to be negligible during this period.…”

“…Hence this study focuses on aspects of the response that appear to be less sensitive to those interactions as they are relatively robust across the models (despite some emission-driven models using interactive aerosols while others used climatological fields). Many PDRMIP studies have taken this approach Myhre et al, 2017;Stjern et al, 2017;Liu et al, 2018;Richardson et al, 2018), though further work with models incorporating more realistic aerosol-cloud in-teractions would of course be valuable in determining the veracity of all conclusions from the project.…”

Arctic Amplification Response to Individual Climate Drivers

“…The greater impact of European emissions is likely due to factors connected with the nearer proximity of Europe to the Arctic but may also be related to a saturation of aerosol‐cloud interactions over East Asia, as well as a greater climatological cloud cover, which could mask the direct aerosol forcing in that region (Kasoar et al, ). In another PDRMIP analysis, Liu et al () also found that the forcing from European SO 4 increases had a stronger efficacy in terms of global temperatures and precipitation effects than that from the Asian region. In the present study, we find that the concentration‐based models do not show this difference, at least in the Arctic.…”

“…The Precipitation Driver Response Model Intercomparison Project (PDRMIP) (Myhre et al, ) provides a unique data set that allows for investigations into climate responses to separate and clearly defined climate drivers, such as greenhouse gases or aerosols, in a multimodel framework. This has led the way for several studies that have investigated various aspects of climate driver‐response relationships from a global perspective (Liu et al, ; Samset et al, ; Samset et al, ; Stjern et al, ). Here we use the PDRMIP data set to analyze the climate response in the Arctic (defined as the region north of 60°N).…”

Contrasting Tropical Climate Response Pattern to Localized Thermal Forcing Over Different Ocean Basins

“…The ITCZ shifts toward a warmer hemisphere in all ocean basins regardless of the spatial pattern of surface heating anomalies, whether an external forcing is spread over the entire North Atlantic region or concentrated in a narrow region along the Gulf Stream (L'Hévéder et al, 2015). Sulfate aerosols over Asia leads the ITCZ to shift southward across the Pacific, Atlantic, and Indian Ocean basins (Liu et al, 2018). Sulfate aerosols over Asia leads the ITCZ to shift southward across the Pacific, Atlantic, and Indian Ocean basins (Liu et al, 2018).…”