Credit: CC0 Public DomainYale University has just published a study that suggests that aerosols in our atmosphere could temporarily cool the ocean temperature in the eastern equatorial Pacific.These findings were published in Nature Climate Change. They suggest that the modest warming seen in the tropical Pacific over the past decade may have been temporary and that there will be more drastic changes. These results may also help climate scientists to make better predictions about how global warming will impact weather patterns, ecosystems and storm impacts across the Pacific Rim.Ulla Heede (first author), a Yale graduate student in the Department of Earth & Planetary Sciences, stated that scientists must understand how the tropics are changing as a result of global warming.Alexey Fedorov is a Yale climate scientist and professor of ocean and atmospheric sciences at the Faculty of Arts and Sciences. He is also the study's senior author. Fedorov's research focuses on global weather systems and phenomena, such as the Atlantic meridional turning circulation, which is one of the largest water circulation systems on the planet, and El Nio events.Fedorov and Heede focus their new study on the eastern equatorial Pacific Ocean. This region is characterized by cold waters that rise to the surface driven by trade winds. These winds are periodically relaxed, resulting in El Nio, which is the warm phase, unusually warm water, of the El Nio Southern Oscillation.If the eastern Pacific heats faster than the surrounding oceans, this indicates a slower pace of atmospheric tropical circulation called the Walker circulation. This results in a decrease in both the trade winds as well as the amount of cold waters rising from the ocean bottoms.Fedorov stated that a slowdown in tropical circulation would lead to changes to El Nio events, and the tropical rain belt. These changes will affect all societies in the tropics, and further afield.Despite numerous climate models predicting a slowdown, it has not yet occurred. The region actually has warmed less than the surrounding areas, or even cooled, in recent decades while the tropical atmospheric circulation has strengthened. It begs the question, "Is this natural climate variability? Or are there other factors at play?"The Yale study found that it was atmospheric aerosols. These are tiny particles that can be emitted from multiple sources including human activities.Heede stated that it is well-known that aerosols from combustion and air pollution have a cooling effect on Earth's climate. He also said that they have partially cancelled out some warming effects of greenhouse gases since preindustrial times. Our study shows that aerosols may be contributing to the delay of eastern Equatorial warming, and the slowdown in tropical circulation. This is something that would not have happened otherwise.Heede said, "It's important to remember that this delay in the implementation of climate change policies is temporary." As greenhouse gas emissions rise further, they will be the dominant factor in tropical Pacific climate. This could lead to an increase in eastern Pacific warming.Researchers believe that eastern Equatorial warming delays will persist for many decades.Fedorov and Heede suggested that there could be a thermostat-like mechanism in the tropical Pacific, which is contributing to the slowing down of warming. Trade winds cause cold water to rise in the eastern equatorial region of the Pacific. Global warming means that the deeper oceans warm slower than the surface waters. This contributes to a delay of warming the eastern equatorial Pacific while the temperature in the western equatorial Pacific continues rising. These two factors are critical to the strength of the trade winds. They depend on the east/west ocean temperature contrast and maintain the upwelling relatively cooler waters until that ocean is warm enough to overcome the effect.The researchers used datasets from the Coupled Model Intercomparison Project (6CMIP6) for the study. This is a long-term international climate research program that uses a collection of 40 climate models. Researchers conducted climate simulations for historical periods and projected future climate scenarios.Continue reading Scientists are more confident in projecting ENSO changes as a result of global warmingInformation: Ulla K.Heede et. al., Eastern equatorial Pacific heating delayed by aerosols, and thermostat response to carbon dioxide increase, Nature Climate Change (2021). Information from Nature Climate Change Ulla K.Heede et. al., Eastern equatorial Pacific heating delayed by aerosols, and thermostat response to carbon dioxide increase, (2021). DOI: 10.1038/s41558-021-01101-x
