Aerosol-forced AMOC changes in CMIP6 historical simulations.

Menary, Matthew; Robson, Jon; Allan, Richard P.; Booth, Ben B. B.; Cassou, Christophe; Gastineau, Guillaume; Gregory, Jonathan M.; Hodson, Daniel L. R.; Jones, Colin; Mignot, Juliette; Ringer, Mark A.; Sutton, Rowan; Wilcox, Laura; Zhang, R.

doi:10.5194/egusphere-egu2020-2379

Cited by 27 publications

(57 citation statements)

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“…A similar compensating effect by air‐sea heat flux was shown before for the case of GHGs induces NAWH (Gervais et al, 2018; Menary & Wood, 2018). Hence, we conclude that the local increase in surface temperature over the North Atlantic is caused by changes in the ocean heat flux (in agreement with previous studies; Cai et al, 2006; Delworth & Dixon, 2006; Menary et al, 2020). This is also consistent with previous studies (Caesar et al, 2018; Chemke et al, 2020; Cheng et al, 2013; Drijfhout et al, 2012; Gervais et al, 2018; Marshall et al, 2015; Menary & Wood, 2018; Piecuch et al, 2017; Rahmstorf et al, 2015; Robson et al, 2016; Woollings et al, 2012) showing that the NAWH is driven by a reduction in meridional heat flux in the ocean.…”

Section: Resultssupporting

confidence: 93%

“…In addition, we note that in the Full-forcing case the ensemble mean temperature difference demonstrates a reduction between 1920 and 1960, followed by a recovery up to 1990. This trend is consistent with the strongest aerosol effect on the AMOC during the latter period (Menary et al, 2020).…”

Section: 1029/2020gl090778supporting

confidence: 88%

“…We note that large uncertainties regarding the magnitude and spatial distribution of the aerosol forcing remain (Bellouin et al, ). A recent paper showed that the strength of the aerosol forcing in the different models and, in particular the representation of aerosol‐cloud interactions, can have a strong effect on the aerosol‐driven strengthening of the AMOC (Menary et al, 2020). Since the location of the warming hole is different in the different models (Figure 1), in Figure 2, we present the analysis of the local temperature contrast around its location in the multimodel mean.…”

Section: Resultsmentioning

confidence: 99%

“…A temperature increase in the North Atlantic due to aerosol forcing (Figures 1 and 2) could be caused either by air‐sea heat flux changes or by changes in the ocean heat flux (especially of the AMOC; Cai et al, 2006; Delworth & Dixon, 2006; Menary et al, 2020). Figure 3 presents the changes in all the different components of the air‐sea flux (sensible heat Q SH , latent heat Q LH , surface radiative longwave

F_{LW}^{SFC}

, and radiative shortwave flux

F_{SW}^{SFC}

changes) and its sum.…”

Section: Resultsmentioning

confidence: 99%

“…However, despite differences in forcing structure, previous studies demonstrated a similar spatial pattern of response of surface temperature to GHGs and aerosol forcing (with an opposite sign; Xie et al, 2013). Specifically, aerosol forcing was shown to strengthen the AMOC and hence to oppose the GHGs effect (Cai et al, 2006; Delworth & Dixon, 2006; Menary et al, 2020). The aerosol strengthening of the AMOC was explained by a combination of temperature and salinity effects on the sea water density in the North Atlantic (Delworth & Dixon, 2006).…”

Section: Introductionmentioning

confidence: 99%

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Aerosol Forcing Masks and Delays the Formation of the North Atlantic Warming Hole by Three Decades

Dagan

Stier

Watson-Parris

2020

Geophysical Research Letters

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The North Atlantic warming hole (NAWH) is referred to as a reduced warming, or even cooling, of the North Atlantic during an anthropogenic-driven global warming. A NAWH is predicted by climate models during the 21st century, and its pattern is already emerging in observations. Despite the known key role of the North Atlantic surface temperatures in setting the Northern Hemisphere climate, the mechanisms behind the NAWH are still not fully understood. Using state-of-the-art climate models, we show that anthropogenic aerosol forcing opposes the formation of the NAWH (by leading to a local warming) and delays its emergence by about 30 years. In agreement with previous studies, we also demonstrate that the relative warming of the North Atlantic under aerosol forcing is due to changes in ocean heat fluxes, rather than air-sea fluxes. These results suggest that the predicted reduction in aerosol forcing during the 21st century may accelerate the formation of the NAWH. Plain Language Summary Anthropogenic aerosols are particles suspended in the atmosphere, which were released due to anthropogenic activity. These particles have a general cooling effect on the Earth due to their interactions with radiation and with clouds. Here we show that the surface temperature in the North Atlantic Ocean is predicted to increase due to aerosol forcing (despite the global cooling). This trend is the opposite of the surface temperature trend predicted due to increase in greenhouse gases (global warming with a warming "hole" in the North Atlantic, trend known as the North Atlantic warming hole-NAWH). Using state-of-the-art climate models, we show that aerosol forcing delays the formation of the NAWH by about 30 years. This trend could have important climatic impacts due to the key role of the North Atlantic surface temperatures in setting the Northern Hemisphere's climate and due to the predicted reduction in aerosol forcing in the next few decades.

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