A rare “triple dip” La Niña, which kept Pacific Ocean temperatures low for three consecutive years, may have set the stage for a significant rise in global heat observed in 2023.

While a rise in global temperatures was anticipated due to greenhouse gas emissions and warm surface waters, a peak was not expected until early 2024. From September 2023 indicates this surge has come earlier than forecasted.

Julius Mex from the University of Leipzig, Germany, and his team sought to understand the events of late 2023 that triggered this exceptional heat. “Our goal is to clarify why temperature changes in the Northern Decay were so extreme,” he states.

Utilizing a dataset that amalgamates historical weather records with climate models, the research team explored various factors, including the Pacific’s circulation, temperature, cloud coverage, radiation, and precipitation for the years 2022 and 2023.

The findings suggest that the Pacific’s cool La Niña conditions, persisting since 2020, were pivotal. They suppressed ocean warmth, fostered the creation of lowland clouds, and enhanced solar radiation reflection.

When the El Niño pattern emerged in 2023, the shift from La Niña to El Niño was so pronounced that it affected air circulation and precipitation patterns in the Western Pacific, releasing more heat into the atmosphere than initially expected.

Simultaneously, this transition led to a sharp decrease in cloud coverage over the Eastern Pacific Ocean, allowing for enhanced absorption of solar radiation. “This could drive significant annual temperature fluctuations,” notes Mex.

Karsten Hautin from Leipzig University, although not involved in the research, expressed agreement with the conclusions. “With a triple dip La Niña, the ocean fails to release heat,” he explains. “As a result, heat accumulates in the deeper ocean layers before eventually surfacing.”

Mex emphasizes that their findings indicate the reduction of ocean cloud cover as a critical element in the sharp temperature increase observed in 2023. “It fits perfectly,” he concludes.

Richard Allan from the University of Reading in the UK notes advances in understanding how cloud coverage shifted over the Pacific in 2022 and 2023. Nevertheless, he highlights that anthropogenic climate change, alongside decreases in cooling aerosol pollution, significantly contributes to diminished ocean cloud cover and escalating temperatures.

“The magnitude of the global temperature rise in 2023 resulted not only from heightened planetary heating due to increased greenhouse gases but also from the reduction and dimming of clouds connected with decreasing aerosol particle pollution,” Allan remarks.