PHL Seas Hit Record Heat After El Niño

By Francis Allan L. Angelo

A new study has revealed that marine heatwaves persisted in Philippine waters for up to three months after the 2023-2024 El Niño ended, setting new records for sea surface temperatures and raising alarm over marine ecosystem stress.

The research, titled “Evolution of Marine Heatwave in the Philippines During and After the 2023/24 El Niño”, was conducted by scientists from the University of the Philippines Marine Science Institute and funded by the Department of Science and Technology – PCAARRD.

Rachel Francisco, Dr. Charina Lyn Amedo-Repollo, and Chloie Ann Libatog of the Physical Oceanography and Observation Laboratory worked with Dr. Maria Vanessa Baria-Rodriguez of the Interactions of Marine Bionts and Benthic Ecosystems Laboratory to investigate marine heatwaves in the Philippines.

The research was recently published in the IOP Conference Series: Earth and Environmental Science.

According to the study, daily sea surface temperatures (SSTs) peaked at 30.45°C in mid-June 2024, surpassing historical records including the 2015-2016 El Niño event.

Using satellite-derived data from the Operational Sea Surface Temperature and Ice Analysis Near Real-Time (OSTIA-NRT) dataset, researchers tracked SSTs from March 2023 to August 2024 to assess the evolution of marine heatwaves (MHWs) in the region.

PAGASA issued an El Niño Watch in March 2023, with the event officially beginning in July and peaking between November 2023 and January 2024, before returning to neutral conditions in May 2024.

Despite the El Niño’s official end, anomalously high SSTs persisted across the archipelago through August 2024, driven by residual El Niño warming and the onset of the southwest monsoon.

The study identified two main clusters of MHW anomalies: the first occurred from November 2023 to January 2024 during the northeast monsoon season, and the second, more intense group appeared from April to August 2024.

Researchers observed that MHWs typically formed in the north and migrated southward, with the second group showing broader spatial coverage and intensity, particularly west of the country.

Although the northeast monsoon typically cools northern waters, it was insufficient to counteract El Niño-induced warming, resulting in sustained heat anomalies in northwest Philippine waters.

By contrast, the southwest monsoon brought warm, moist air that intensified SSTs, sustaining marine heatwaves well beyond the El Niño’s conclusion.

Globally, SSTs reached a record-high average of 21.09°C in February 2024, according to the European Centre for Medium-Range Weather Forecasts, but the Philippines recorded daily peaks nearly 10°C higher.

Marine heatwaves are defined as prolonged periods of unusually warm ocean temperatures exceeding the 90th percentile threshold over a 30-year climatology for at least five consecutive days.

These extreme events are known to disrupt marine food chains, cause mass coral bleaching, and alter breeding and migration cycles of marine species.

The National Oceanic and Atmospheric Administration (NOAA) declared the fourth global coral bleaching event in April 2024, with observations of “bleaching-level heat stress” across the Pacific, Atlantic, and Indian Oceans.

In the Philippines, the heat index soared to 55°C in April 2024, and below-normal rainfall intensified drought-like conditions in various provinces.

Previous studies have shown a sharp rise in marine heatwave occurrences in the Philippines, from just seven in the 1980s to 37 in the 2010s, with the strongest events linked to El Niño phases.

This latest study points to the compounded effects of global climate patterns like El Niño and local monsoon systems in intensifying MHWs in the Philippine maritime domain.

The authors emphasized that understanding these compound drivers is critical for designing marine conservation efforts and preparing adaptive strategies for ecosystems under escalating climate pressure.

Experts warn that without rapid emissions reduction and enhanced ocean monitoring, events like these may become more frequent and prolonged in a warming climate.