Warmer Oceans are Not the Positive Spring Breakers May Think
By Erika Pietrzak, June 8, 2025
Our ocean covers around 70 percent of the Earth’s surface, but harbors about ninety percent of global warming. The amount of heat energy the ocean has absorbed over the last six decades is more than eight times the amount of energy humans used over that time period for cooking, electricity, industry, heating, etc.
Source: NASA
Our ocean covers around 70 percent of the Earth’s surface and is a prime example of how global warming is impacting the planet’s life and future. According to NASA, about ninety percent of global warming is occurring in the ocean. Since 1992, the ocean’s heat content has increased by 287 zettajoules. The amount of heat energy the ocean has absorbed over the last six decades is more than eight times the amount of energy humans used over that time period for cooking, electricity, industry, heating, and more. In fact, the last decade has seen the warmest ocean temperatures since at least the 1800s, with 2024 marking the warmest year for the ocean on record. This warming is not just alarming on paper, but negatively impacts hundreds of millions of people worldwide.
The ocean has a tremendous ability to store and release heat over extended periods of time. This places the ocean in a central role in stabilizing Earth’s climate system. However, its ability to retain heat means that changes to the ocean can have delayed impacts, making it difficult for many individuals to understand how their actions affect ocean ecosystems. The ability of the ocean to retain heat results in the ocean's heat content constantly increasing, meaning “the atmosphere has been spared from the full extent of global warming for now.” Across the globe, the North Atlantic Ocean, Indian Ocean, Arctic Ocean, and Southern Oceans experience hotter ocean temperatures than the rest of the world’s waters.
The upper layers of the ocean account for about 63 percent of the total increase of the amount of stored heat in ocean systems from 1971 to 2010, with the next 700 meters holding another 30 percent of that heat. The top 700 meters of our oceans have warmed about 1.5 degrees Fahrenheit since 1901. Heat accumulates faster in the upper layers (where most of the marine life exists), but is averaged over the full depth of the ocean through the movement caused by waves.
Source: NOAA
The 1.5 degree increase since 1901 is “enough to transform marine biodiversity, change ocean chemistry, raise sea levels, and fuel extreme weather.” This heat does not dissipate, but rather moves into new spaces. Warming temperatures in the ocean cause the water molecules to expand, which is responsible for one third to one half of global sea level rise. Scientists estimate that sea levels could rise by 15 inches by 2100. In addition to this, scientists recently discovered that the warming of the top 6,500 feet of the ocean to be about 40 percent higher than previously estimated. This resulted in an average rise of 4.5 millimeters between 2013 and 2021.
Whether its thinning ice shelves, evaporating water, melting glaciers, or direct reheating of the atmosphere, exchanges of heat affect every aspect of the ocean. The Arctic is warming three times faster than the global average, despite air temperatures only being twice the global average. The melting of snow and ice exposes darker sea ice, resulting in an increase in solar energy absorbed due to the increased albedo of these surfaces. Moreover, the geographic heat distribution “in the Arctic strongly suggests that the decrease in sea ice coverage has enhanced the warming.”
Rising ocean temperatures are responsible for increasingly intense hurricanes, heavier rainfall, and stronger snowstorms. These warm waters energize hurricanes and tropical storms, while warmer ocean surface temperatures increase evaporation and atmospheric moisture, boosting precipitation levels. Changes in ocean temperatures have significant repercussions for ocean weather patterns and currents, which will exacerbate extreme weather conditions, whether that be drought or flooding, in regions across the globe. Warming ocean temperatures melt polar ice into the sea, which melts as freshwater and changes the density of the seawater. The fresher, warmer water does not sink as fast or deep as seawater, changing ocean circulation patterns.
Ocean warming does not just cause property damage– it causes loss of life. Aquacultures and fisheries are threatened by these changes, weakening food security for the millions of people who depend on these industries. According to the United Nations, 680 million people live in coastal low-lying areas.
Marine life is also burdened by ocean warming. Marine species are migrating further north to find cooler temperatures and food sources as the ocean grows warmer. Warming oceans “encourage frequent, lengthy marine heatwaves, where temperatures can jump several degrees or more above average.” Marine heatwaves have doubled in frequency and become longer lasting since the 1970s. This increases the likelihood of massive bleaching events. Marine ecosystems are highly sensitive to any changes and this rapid, unprecedented warming is moving too fast for species to adapt to keep up.
Roughly one-third of the atmosphere’s carbon dioxide is absorbed by the ocean. Heating oceans fosters oxygen-depleted dead zones that render them inhabitable to marine life. Warmer oceans also hold more carbon dioxide, which increases acidity in the ocean. Acidification harms corals, snails, and many other marine life forms by dissolving their calcium carbonate shells. The ocean has experienced a 25 percent increase in acidity and today sits at 8.1 (more acidic than the ideal 8.4), which has resulted in mass coral bleaching. Scientists estimate that the ocean could lose 70 to 80 percent of its coral reefs by 2045.
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