Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability

Abstract

Systematic climate shifts have been linked to multidecadal variability in observed sea surface temperatures in the North Atlantic Ocean. These links are extensive, influencing a range of climate processes such as hurricane activity and African Sahel and Amazonian droughts. The variability is distinct from historical global-mean temperature changes and is commonly attributed to natural ocean oscillations. A number of studies have provided evidence that aerosols can influence long-term changes in sea surface temperatures, but climate models have so far failed to reproduce these interactions and the role of aerosols in decadal variability remains unclear. Here we use a state-of-the-art Earth system climate model to show that aerosol emissions and periods of volcanic activity explain 76 per cent of the simulated multidecadal variance in detrended 1860-2005 North Atlantic sea surface temperatures. After 1950, simulated variability is within observational estimates; our estimates for 1910-1940 capture twice the warming of previous generation models but do not explain the entire observed trend. Other processes, such as ocean circulation, may also have contributed to variability in the early twentieth century. Mechanistically, we find that inclusion of aerosol-cloud microphysical effects, which were included in few previous multimodel ensembles, dominates the magnitude (80 per cent) and the spatial pattern of the total surface aerosol forcing in the North Atlantic. Our findings suggest that anthropogenic aerosol emissions influenced a range of societally important historical climate events such as peaks in hurricane activity and Sahel drought. Decadal-scale model predictions of regional Atlantic climate will probably be improved by incorporating aerosol-cloud microphysical interactions and estimates of future concentrations of aerosols, emissions of which are directly addressable by policy actions.

The 2014 Hot, Dry Summer in Northeast Asia

“…The HadGEM3-A response to SST may be exaggerated by a lack of air-sea coupling in the model (e.g., Zhu and Shukla 2013), and the SST changes themselves may have an anthropogenically driven component. In particular, drought in northern China has previously been linked to PDO and AMO variability, which are potentially driven, at least in part, by AA changes (Booth et al 2012;Zhang et al 2013;Allen et al 2014;Boo et al 2015).…”

Imprint of the Atlantic multi-decadal oscillation and Pacific decadal oscillation on southwestern US climate: past, present, and future

“…Although there have been several attempts to deduce the past AMO behavior (Latif et al 2004;Delworth and Mann 2000;Keenlyside et al 2008;Ting et al 2009;Chylek et al 2011Chylek et al , 2012Knudsen et al 2011) its future evolution is uncertain. Booth et al (2012) based on the HadGEM2-ES earth system model simulation suggested that the twentieth century observed Atlantic variability was caused by anthropogenic aerosols. However, Zhang et al (2013) showed that this assumed aerosol driver is not compatible with the observed twentieth century North Atlantic variability.…”

Decreased Response Contrast of Hadley Circulation to the Equatorially Asymmetric and Symmetric Tropical SST Structures during the Recent Hiatus

“…For instance, the contribution from sulfate aerosols (e.g. Booth et al 2012), the North Atlantic Oscillation , the eastern Pacific SST (Kosaka and Xie 2013), Pacific trade winds (England et al 2014), the Interdecadal Pacific Oscillation (Dai et al 2015), and the Pacific Decadal Oscillation (Trenberth and Fasullo 2013). Irrespective of the cause of the hiatus in the past decades, the changes in the temperature may alter the meridional distribution of SST (Adam et al 2014), which may affect the HC in turn.…”