Panama Canal drought was most likely El Niño driven, study finds

• The study's findings demonstrate that not every extreme weather or climate event is primarily tied to human-caused climate change.

Zoom in: During 2023, Panama saw its third-driest year on record, with all but one of the 8 months in the wet season coming in with below-average rainfall in the area of the Panama Canal watershed, the study found.

• Lowering levels of Lake Gatún, critical to the functioning of the canal and serving as a reservoir for Panamanians, caused canal officials to reduce the number of ships that transit the canal each day.
• This led to lengthy backups and rerouting that cost both shippers and the canal authority. It also came as instability in the Red Sea made the Suez Canal route especially perilous.

What they did: Researchers from institutions in Panama, the U.S. and Europe examined, via peer-reviewed methods, May through December rainfall in and around the region that feeds into Lake Gatún in central Panama, and how that has varied over time.

What they found: The data established clear ties between the drought in Panama and El Niño, which is a natural climate cycle characterized by unusually warm waters in the tropical Pacific Ocean, along with large-scale shifts in weather patterns.

• Increasing demand for water from a growing population also played a role, the study found.
• El Niño doubled the likelihood of the low 2023 rainfall, the researchers concluded.
• No clear long-term precipitation trends emerged in the observational record, and computer models simulating today's climate versus a preindustrial world showed high variability. This prevented scientists from teasing out a climate change signal.
• "With neither climate model data nor a strong physical argument... we therefore cannot conclude that the observed drying is attributable to human-caused climate change," the researchers wrote in their main findings.

Between the lines: The climate study is from the World Weather Attribution group. Scientists affiliated with this project have found that human-caused climate change has boosted the odds and severity of many highly impactful extreme weather and climate events, particularly heat waves and heavy precipitation events.

• Some have criticized this loose-knit group of scientists for consistently finding climate change links to extreme events, despite sparse observational records in an area.

• However, this new study may give the group added credibility by showing it followed the data where it leads. In this case, it ended up showing a weak to nonexistent link to human-caused global warming.
• It isn't the first time the attribution teams have not pinned the blame on climate change, but it is a prominent case since the backups at the Panama Canal got so much attention.

There has been an uptick in the occurrence of large storms, which dump especially heavy rainfall in Panama. That is consistent with what's expected due to human-caused climate change.

• Still, the researchers have relatively high confidence in their work, given the abundance of long-term observational data they had access to.

What they're saying: "The low rainfall last year is another unique example of a weather event that was worsened by El Niño, but not in a significant way by climate change," said Friederike Otto, a climate scientist at Imperial College London who heads up the attribution group, said in a statement.

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