Ocean Thermal Extremes in the Philippines during the Warmest Recorded Years

Marine heatwaves (MHWs) and marine cold spells (MCSs) represent critical ocean thermal extremes with profound ecological and socioeconomic consequences, yet their regional characteristics and drivers remain poorly constrained in many tropical, biodiversity-rich regions. The Philippines, located at the center of global marine biodiversity, is particularly vulnerable to such extremes but has received limited attention in high-resolution analyses, especially during recent exceptionally warm years. In this study, we investigate the spatiotemporal characteristics of MHWs and MCSs in Philippine waters using the Global Ocean Physics Reanalysis from the Copernicus Marine Environment Monitoring Service (CMEMS) at 0.083° × 0.083° spatial resolution. Events are detected following percentile-based definitions using a recent climatological baseline period (1993–2022), with particular emphasis on the warmest years on record (2023–2025).

Our analysis reveals pronounced regional contrasts in the frequency, intensity, and duration of MHWs and MCSs across the Philippine seas, reflecting the strong influence of local ocean–atmosphere interactions and basin-scale circulation. MHWs exhibit increasing persistence and intensity during recent years, while MCSs display asymmetric behavior consistent with long-term ocean warming. The enhanced spatial resolution captures fine-scale coastal and shelf processes that are unresolved in coarser products, reducing uncertainties in the detection of thermal extremes and highlighting localized hotspots of extreme warming and cooling.

This work aims to improve understanding of how large-scale ocean–atmosphere variability manifests as regional thermal extremes in a tropical, archipelagic setting. By providing an updated, high-resolution characterization of both warming and cooling extremes during the warmest recorded years, the study contributes to ongoing efforts to improve monitoring, predictability, and risk assessment of ocean thermal extremes in biodiversity-rich and socioeconomically vulnerable regions such as the Philippines.