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Abstract El Niño/Southern Oscillation variability has conspicuous impacts on ecosystems and severe weather. Here, we probe the effects of anthropogenic aerosols and greenhouse gases on El Niño/Southern Oscillation variability during the historical period using a broad set of climate models. Increased aerosols significantly amplify El Niño/Southern Oscillation variability primarily through weakening the mean advection feedback and strengthening the zonal advection and thermocline feedbacks, as linked to a weaker annual cycle of sea surface temperature in the eastern equatorial Pacific. They prevent extreme El Niño events, reduce interannual sea surface temperature skewness in the tropical Pacific, influence the likelihood of El Niño/Southern Oscillation events in April and June and allow for more El Niño transitions to Central Pacific events. While rising greenhouse gases significantly reduce El Niño/Southern Oscillation variability via a stronger sea surface temperature annual cycle and attenuated thermocline feedback. They promote extreme El Niño events, increase SST skewness, and enlarge the likelihood of El Niño/Southern Oscillation peaking in November while inhibiting Central Pacific El Niño/Southern Oscillation events. 

Abstract In the era of escalating climate change, understanding human impacts on marine heatwaves (MHWs) becomes essential. This study harnesses climate model historical and single forcing simulations to delve into the individual roles of anthropogenic greenhouse gases (GHGs) and aerosols in shaping the characteristics of global MHWs over the past several decades. The results suggest that GHG variations lead to longer-lasting, more frequent, and intense MHWs. In contrast, anthropogenic aerosols markedly curb the intensity and growth of MHWs. Further analysis of the sea surface temperature (SST) probability distribution reveals that anthropogenic GHGs and aerosols have opposing effects on the tails of the SST probability distribution, causing the tails to expand and contract, respectively. Climate extremes such as MHWs are accordingly promoted and reduced. Our study underscores the significant impacts of anthropogenic GHGs and aerosols on MHWs, which go far beyond the customary concept that these anthropogenic forcings modulate climate extremes by shifting global SST probabilities via modifying the mean-state SST. 

Abstract The Pacific Decadal Oscillation has been suggested to play an important role in driving marine heatwaves in the Northeast Pacific during recent decades. Here we combine observations and climate model simulations to show that marine heatwaves became longer, stronger and more frequent off the Northeast Pacific coast under a positive Pacific Decadal Oscillation scenario, unlike what is found during a negative Pacific Decadal Oscillation scenario. This primarily results from the different mean-state sea surface temperatures between the two Pacific Decadal Oscillation phases. Compared to the cool (negative) phase of the Pacific Decadal Oscillation, warmer coastal sea surface temperatures occur during the positive Pacific Decadal Oscillation phase due to reduced coastal cold upwelling and increased net downward surface heat flux. Model results show that, relative to the background anthropogenic global warming, the positive Pacific Decadal Oscillation in the period 2013–2022 prolongs marine heatwaves duration by up to 43% and acts to increase marine heatwaves annual frequency by up to 32% off the Northeast Pacific coast.