The world has witnessed an unprecedented surge in marine heatwaves (MHWs) over the past two years, with a staggering 240% increase in the number of MHW days during the summers of 2023-2024 compared to historical records. A recent study published in Nature Climate Change warns that nearly 10% of the world’s oceans have recorded the highest sea surface temperatures (SSTs) ever observed four times higher than the historical annual average.
The primary driver behind this alarming trend is human-induced climate change, which has been further amplified by El Niño a natural climate phenomenon in the Pacific Ocean known for warming sea surface temperatures and record-low global cloud cover.
Escalating Ocean Heatwaves and Their Devastating Consequences
Marine heatwaves occur when ocean temperatures rise abnormally high for prolonged periods, disrupting marine ecosystems and weather patterns. The study highlights that the extreme warming in 2023-2024 triggered at least 100 physical, biological, and societal impacts worldwide.
The prolonged ocean heatwaves contributed to extreme air temperatures in the UK, North America, and Japan, along with severe flooding in Ecuador, Libya, Japan, and Australia. These extreme conditions also fueled devastating storms, including Cyclone Gabrielle, which resulted in 11 deaths and caused damage worth over 14 billion New Zealand dollars.
In the Indian Ocean, marine heatwaves intensified tropical cyclones, including Cyclone Mocha in May 2023 and Cyclone Remal in May 2024. Scientists warn that the Indian Ocean is warming at an alarming rate 1.2°C per century since 1950, with projections suggesting a rise of 1.7°C-3.8°C per century by 2100. The northwestern Indian Ocean, particularly the Arabian Sea, is expected to experience even more severe impacts, with MHW events potentially lasting up to 250 days per year, pushing the region toward a near-permanent heatwave state.
Impact on Marine Life: Mass Mortalities, Coral Bleaching, and Ecosystem Collapse
The prolonged marine heatwaves of 2023-2024 had severe consequences for marine life. Widespread coral bleaching events were recorded, leading to the destruction of vital ecosystems in Japan and Peru. The Gulf of Thailand and the Gulf of Mexico experienced mass fish die-offs, while disruptions in phytoplankton productivity in the North Atlantic raised concerns about long-term impacts on fish and seabird populations.
Several species were forced to migrate to cooler waters. In the North Atlantic, marine species moved into Arctic regions, while the South Pacific witnessed a rise in whale and dolphin strandings. In the Mediterranean Sea, rising ocean temperatures triggered a disease outbreak that threatened the extinction of the fan mussel the region’s largest shellfish.
Economic Fallout: Fisheries and Tourism Take a Hit
The economic consequences of marine heatwaves have been severe, affecting fisheries, aquaculture, and marine tourism. In Peru, shifting anchovy populations forced a shutdown of commercial fisheries, causing an estimated loss of $1.4 billion. The global coral bleaching event negatively impacted snorkeling and scuba diving tourism, forcing the closure of several diving hotspots. Aquaculture industries in the Mediterranean Sea and the Gulf of Thailand also suffered significant losses.
Despite these escalating threats, the study reveals that most affected regions lacked proper response strategies. Many governments and organizations failed to issue timely warnings or implement mitigation measures due to limited resources, lack of coordination, and poor communication among institutions.
Urgent Need for Better Forecasting and Climate Action
The researchers emphasize the need for improved forecasting systems to provide longer preparation windows for policymakers and industries. While forecasts for 2023-2024 were generally accurate, some critical misses led to inadequate disaster response.
With marine heatwaves expected to become more frequent and severe in the coming decades, scientists call for immediate action to mitigate their impacts. Strengthening global efforts to reduce greenhouse gas emissions, implementing early warning systems, and developing adaptation strategies for vulnerable regions are crucial steps to address this growing crisis.
If left unchecked, marine heatwaves could push the world’s oceans into a new era of extreme and unpredictable conditions, with dire consequences for marine biodiversity, coastal communities, and the global economy.