The ability of the world’s marine life to cope with global temperatures in the first full year in which they exceeded the 1.5°C Paris Agreement threshold has been revealed in a new study by King Abdullah University of Science & Technology (KAUST) in Saudi Arabia. The short answer? Not well.
The university’s assessment of marine ecosystems’ response to extreme heat is said to be one of the first to be published. It involved analysing 201 ecological-impact events that occurred worldwide between July 2023 and June 2024.
This coincided with year-round marine heat extremes across much of the ocean, with almost a third of the 201 events occurring outside the tropics, in what have traditionally been cooler ecosystems.
This, according to KAUST, means that environmental monitoring, which has traditionally focused on summer heat extremes, now misses a significant part of the picture.
Mass mortality
Harmful effects were found to range from coral bleaching and algal blooms to species mortality, habitat disruption and fisheries impacts.
More than half of all the events studied ended in mass mortality. The proportion of coral-bleaching events resulting in substantial mortality was almost three times higher than during the previous global bleaching event of 2014-2017.
No major marine ecosystem was spared, says KAUST, including places scientists had previously considered safe. Eighteen of the 50 coral-reef regions globally designated as most resistant to climate change were adversely affected, raising serious questions about existing conservation strategies.
Nearly a quarter of the events directly impacted fisheries and aquaculture, with a single disease outbreak in Norway causing estimated losses of $2 billion.
The researchers found that 98% of documented ecological impacts were associated with unusually warm sea temperatures, though other drivers such as major storms and other extreme weather events played a part in the negative outcomes.
Unintended consequence
An unintended consequence of the research was said to be that it identified potential patterns of heightened vulnerability and exposure across different ecosystems and regions. This could help scientists and policy-makers better understand where ecological and socio-economic risks might increase if global warming remains static or goes on rising, says KAUST.
The international team of scientists drew on data from scientific literature, monitoring programmes and documented observations from around the world, resulting they say in one of the biggest and most comprehensive such records ever assembled.
Research scientist Dr Shannon Klein was lead author of the paper, just published in One Earth. “This study provides a real-world snapshot of how marine ecosystems responded during an exceptional period of ocean warmth,” she said.
“One of the clearest findings was that impacts were not confined to traditional summer heat extremes. We found evidence of ecological disruption across seasons, which suggests that understanding and responding to ocean warming requires year-round monitoring and assessment.”
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