The El Niño phenomenon, in the context of climate change and a decrease in atmospheric aerosols, is believed to be the driving force behind many recent climate records.
In recent weeks, climate records have been shattered globally. On July 4, a new record was set for the highest global average temperature, surpassing the previous record from July 3. The average sea surface temperature also reached an all-time high, while Antarctic sea ice coverage hit a record low.
Pedestrians seeking shade in Beijing on July 6. (Photo: Jiang Qiming/China News Service/VCG)
On the same day, July 4, the World Meteorological Organization declared the onset of El Niño, paving the way for a surge in global temperatures and disruption of weather and climate patterns. In the context of global warming, El Niño conditions amplify the effects, pushing temperatures to new heights. This is accompanied by a decrease in aerosol levels, which are tiny particles that can redirect solar radiation. Therefore, these two factors are likely responsible for the record heat experienced in both the atmosphere and the oceans.
The rapid warming we are witnessing is largely due to the ongoing El Niño phenomenon, combined with the warming trend caused by greenhouse gas emissions from human activities. Researchers have identified El Niño when sea surface temperatures in various regions of the Pacific warm significantly. Warmer sea surface temperatures contribute to higher average temperatures on land.
The most recent strong El Niño event occurred in 2016, but since then, we have emitted 240 million tons of CO2 into the atmosphere. El Niño does not create additional heat but redistributes existing heat from the ocean into the atmosphere. The vast ocean, which covers 70% of the planet’s surface, can store enormous amounts of heat due to its particularly high thermal capacity. This is why 90% of the excess heat from global warming is absorbed by the oceans.
The heat circulation currents between the Earth’s surface and the deep sea play a crucial role. During an El Niño event, trade winds over the Pacific weaken, and the upwelling of cold water along the South American Pacific coast diminishes. This results in warming of the upper layers of the ocean.
Higher than normal sea surface temperatures were recorded in the first 400 meters of the Pacific Ocean in June 2023. Because cold water is denser than warm water, this warm layer prevents colder seawater from rising to the surface. The warm seawater in the Pacific also leads to increased storm activity, releasing more heat into the atmosphere through a process known as latent heat. This means that the heat accumulated from global warming, which had been stored in the ocean during the recent La Niña event, is now being released into the surface waters, breaking records.
Another factor certainly contributing to the unusual warming is the decrease in aerosols across the Atlantic Ocean. Aerosols are tiny particles that can redirect incoming solar radiation. Injecting aerosols into the stratosphere is one of the geoengineering measures that humans can employ to mitigate the impacts of global warming, although reducing greenhouse gas emissions is still far more effective.
The absence of aerosols can also lead to increased temperatures. A 2018 study concluded that 35% of the sea surface temperature changes in the Atlantic during the Northern Hemisphere summer could be explained by changes in Saharan dust. Recent levels of Saharan dust over the Pacific have been unusually low. Similarly, new international regulations on sulfur particle emissions from marine fuels introduced in 2020 have led to a global decrease in sulfur dioxide emissions. The combination of these factors is why many average surface temperature records are being challenged.
