Oceans feel the heat from human climate pollution

Heating up

By absorbing over 90 percent of the excess heat trapped in the atmosphere by greenhouse gases, oceans are warming at an accelerating rate. According to Angelique Melet, an oceanographer at the European Mercator Ocean Monitor, the rate of ocean warming has more than doubled since 1993, as reported by the UN's IPCC climate expert panel. Average sea surface temperatures reached new records in 2023 and 2024, and despite a brief respite at the start of 2025, temperatures remain historically high.

The Mediterranean Sea has recorded new temperature highs for the past three years, alongside the North Atlantic and Arctic oceans. Marine heatwaves have doubled in frequency, lasting longer and affecting a wider area. Warmer seas can intensify storms, while the rising temperatures devastate species like corals and seagrass beds, which cannot migrate. Scientists predict that 70 to 90 percent of corals may be lost this century if global warming reaches 1.5 degrees Celsius, a threshold expected to be breached in the early 2030s.

Relentless rise

As liquids and gases warm, they expand and occupy more space. In oceans, thermal expansion, combined with the melting of ice caps and glaciers, is causing sea levels to rise. Research indicates that the pace of ocean rising has doubled in the last three decades and could double again by 2100, potentially reaching about one centimeter per year. Approximately 230 million people live less than a meter above sea level, facing increasing risks from floods and storms. Melet emphasizes that ocean warming and sea-level rise are inescapable processes, but reducing greenhouse gas emissions can mitigate the damage and provide time for adaptation.

More acidity, Less Oxygen

The ocean not only stores heat but has also absorbed 20 to 30 percent of human carbon dioxide emissions since the 1980s, leading to increased acidity. This acidification weakens corals and complicates the calcification process for shellfish, crustaceans, and certain plankton. Oxygen concentration in ocean waters is another critical indicator, as its loss is linked to warming waters and other complex factors.

Reduced sea ice

Mid-February saw a record low in combined Arctic and Antarctic sea ice cover, dropping more than a million square miles below the pre-2010 average. This reduction creates a vicious cycle: less sea ice allows more solar energy to warm the water, leading to further ice melt. This phenomenon, known as "polar amplification," accelerates global warming, particularly at the poles, as explained by Guinaldo.