NEW ORLEANS — Extreme coastal flood events, historically occurring with a 1% annual probability, are now approximately 12 times more likely, according to a study published in the journal Nature Climate Change. Human-driven climate change has increased the likelihood of these events by a factor of four.

The Nature Climate Change study analyzed long-term tide gauge records from over 100 sites alongside climate models. This research evaluated data collected from 1900 to 2005. The study concluded its data analysis in 2005 due to limitations in climate models that can attribute events to human-driven climate change beyond that year. Researchers determined that sea level changes in the early 20th century were primarily driven by natural forces, but human contributions to coastal extremes have increased since 2005, suggesting current risks are likely higher than the study's findings indicate.

Since the 1960s, human-caused warming has been the primary driver of rising sea levels. Ben Strauss, chief scientist, said, "Essentially every coastal flood today has human fingerprints on it through climate change. Without the extra bit of sea level rise caused by global heating, most of these events would not have reached the status of flood."

A separate study in the journal Science Advances found that climate change accounted for 58% of days with extreme water levels between 2000 and 2018. This study also found that climate change has nearly tripled the average number of days exceeding extreme water level thresholds since the 1970s. Sönke Dangendorf, an associate professor, stated that greenhouse gas emissions from burning fossil fuels represent the primary human factor driving sea level rise. He added, "In particular since the 1970s, it's by far the dominating factor, and this is of course not good news at the moment. The risk is evolving and with the evolving risk we need to do more for adaptation."

Coastal infrastructure planners must evaluate the financial costs of improving defense systems and determine funding sources to address increasing flood risks. Jeff Williams, a retired oceanographer, stated that the current protections for New Orleans will likely not be adequate beyond the next couple decades. Dangendorf said, "The impacts, even of a relatively little sea level rise, can be pretty impactful on our coasts. There is a silver lining because we have control about how much we emit, right? So we can stop that development, at least to some degree." Global warming trajectories are not currently aligned with the worst-case scenario, but they remain off track to meet best-case emission reduction targets.