Global warming is reflected mainly in the oceans, which absorb almost 90 % of excess heat in the climate system. According to NOAA, 2024 was the warmest year on record for the ocean surface as well – virtually all The oceans have reached record temperatures this year. The European Copernicus service reported that the average annual surface temperature outside the polar regions rose to 20.87 °C (0.51°C above the 1991–2020 normal). Similarly, Berkeley Earth reports that global ocean surface temperatures in 2024 reached approximately +1.15 °C more than pre-industrial levels (1850–1900). This data confirms that the oceans are warming globally faster than ever before.

• NOAA (USA): “2024 was the warmest year on record for the ocean surface as well.” Warming is accumulating at depth: since 1970, the highest values of thermal energy in the ocean (upper 2000 m) have been reached.
• Copernicus (EU): Extra-polar average SST (Sea Surface Temperature) reached in 2024 20.87 °C, which represents a record anomaly of +0.51 °C compared to the reference period.
• Berkeley Earth: Sea surface warming resulted in a record annual anomaly of +1.15°C (compared to 1850–1900), with the steepest increase observed in the data history occurring between 2022–2024.

Scientific connection to climate change

Rising ocean temperatures are linked to potential “climate tipping points” where irreversible changes occur:

• AMOC weakening: The Atlantic Meridional Overturning Circulation (AMOC) carries warm water northward. Several studies warn that AMOC weakening or collapse could occur as early as the mid-21st century. Analyses of climate indicators have shown “strong evidence” that the AMOC is approaching a bifurcation threshold. For example, Danish scientists have warned of the possibility of an “imminent AMOC collapse” between 2025 and 2095, most likely around mid-century. A weakening AMOC would have dramatic consequences – for example, model simulations show that a complete collapse would significantly cool northern Europe and shift tropical rain belts (European winters would be up to 4°C colder). Another effect would be a sharp rise in local sea levels – studies predict an additional ~15–20 cm of sea level rise on the US East Coast just from a weaker AMOC.
• Coral bleaching: Ocean storms and marine heatwaves are causing massive coral bleaching. Already in 2023, temperatures in the Caribbean seas reached extreme values (over 38 °C) and corals lost their symbiotic algae. NOAA warns that in the summer of 2024, Another global wave of coral bleaching – the fourth on record and the most extensive to date. Long-term temperature extremes and increasing acidification are significantly reducing the ability of corals to restore coral reefs, threatening biodiversity and fisheries off the coast of tropical countries.
• Reducing the carbon potential of the oceans: As the ocean warms, its capacity to sequester CO₂ also changes. Model studies show that at high emissions, the anthropogenic ocean carbon synopsis will only result in a limit of ~1 PgC/year, even if CO₂ emissions continue to increase. Warming causes impaired mixing of water layers and lower CO₂ solubility, which in practice means a gradual "depletion" of the ocean's natural capacity to absorb carbon.
• Melting glaciers and rising sea levels: Rapid loss of ice sheets (Greenland, Antarctica) is adding fresh water to the oceans and raising sea levels. This fresh water input is reducing the salinity of the Atlantic, which further threatens the stability of the AMOC circulation (so-called salt feedback). IPCC warns that the loss of ice sheet mass has occurred on a human scale irreversible (even after achieving emission targets, it will take several centuries for the situation to stabilize).

Climatic consequences of ocean warming

The ocean controls both weather and ecosystems. Higher surface temperatures mean more moisture in the atmosphere, stronger storms, and more extreme weather:

• Intense tropical cyclones: Increased energy in the water leads to stronger hurricanes. Studies show that global warming increased the maximum wind speeds of ~80 % Atlantic hurricanes from 2019–2023 by an average of +29 km/h. In 2024, this effect was evident for all eleven Atlantic hurricanes, whose wind speeds increased by approximately 5–23 km/h due to warmer waters. Such intensification represents an enormous increase in potential damage, as each category on the Saffir-Simpson scale carries approximately a fourfold increase in damage (e.g., 2→3).
• Extreme rainfall and floods: Warmer oceans release more water vapor, which fuels more intense storms and torrential rain. The EPA points out that extreme single-day rainfall events have been increasing rapidly in recent decades. In the U.S., the amount of land exposed to single-day rainfall events has been decreasing almost continuously since 1995, and other regions of the world are seeing similar trends. The intense moisture currents are associated with flooding, erosion, and flash floods that destroy infrastructure and agriculture.
• Oceanic heat waves and animal deaths: Long periods of extremely warm water (ocean heat waves) have already led to major changes in ecosystems. For example, the Pacific heat wave (2013–2016) caused massive fish and crab die-offs as planktonic fish populations migrated to cooler waters, and thousands of seal pups and seals starved to death. Ecosystem imbalances spread up the food chain – for example, plankton in the waters are sensitive to temperature and when it is exceeded, their biomass decreases, which also reduces food for larger fish and cetaceans. A good example is the forecast for the Atlantic coastal fisheries in the US: with the current warming trend, the catch will fall by up to 20–30 % by 2060, as thermophilic species migrate north and fishing traditions are disrupted.
• Coral reefs and biodiversity: Corals – the foundation of many food chains in tropical seas – are bleaching and dying as temperatures rise. Massive bleaching (the loss of algae in symbiosis with corals) reduces reefs’ resistance to disease and threatens thousands of species that depend on coral habitats. NOAA already indicated in 2024 the potential for the “most extensive” coral bleaching in history, affecting all oceans.

Future scenarios and the threat of tipping points

Scientists are investigating whether we are approaching irreversible changes:

• AMOC collapse: If the AMOC stability boundary breaks, it will occur sudden climate transition. Some projections speak of a possible collapse of the AMOC as early as around 2050. In such a scenario, for example, Europe would cool significantly (the northern part would contrast with global warming) and the moisture of tropical rains would shift further south. This extreme development would have a local cooling effect ("Europe alone"), but the rest of the world would continue to warm. IPCC SR-Oceans states that the only technically achievable prevention is related to saving fossil fuels - if emissions are reduced, further warming will stop and the risk of such tipping points will decrease.
• Irreversible acidification and the "triple threat": The continued rise in CO₂ is reducing ocean pH (acidification). Some have already decreased by ~0.1 pH since 1850. The IPCC emphasizes that warming, acids and oxygen depletion (deoxygenation) in the ocean are among the phenomena that will remain irreversible for centuries to millennia. The EU-funded COMFORT project warns that the combination of these three factors (the so-called “triple threat”) creates feedback loops with the risk of “irreversible” systemic reversals in the oceans. In other words, if we exceed critical CO₂ concentrations, rapid reef collapses, oxygen depletion and other effects can be triggered, from which the natural system would no longer be able to easily return to its previous trajectory.

Sources: The latest global ocean data and analysis are provided by NOAA and Copernicus, complemented by independent assessments by Berkeley Earth. Climate impacts and potential tipping points are described in current scientific studies (e.g. Rahmstorf et al. on AMOC, Climate Central on hurricanes, Terhaar on the Ocean Carbon Synopsis, or the IPCC and the COMFORT project on irreversible changes). Each of these sources documents the seriousness of ocean warming and the challenges that lie ahead. JRi