World's oceans absorbed a record 23 zettajoules of heat last year, report finds

The world's oceans absorbed a record 23 zettajoules of heat last year, according to a new report, an influx of thermal energy that has left ocean waters hotter, higher and increasingly less hospitable to marine life.

The amount of heat added to the seas was almost 40 times greater than the total energy used by humanity over the same period, illustrating the scale of thermal energy now being absorbed by the world's oceans each year. Researchers say the finding underscores the outsized role oceans play in absorbing excess heat generated by climate change, acting as a buffer that has so far spared the atmosphere from even more extreme warming.

Rising seas and acidification

The report links the record heat uptake to far-reaching changes in the world's deep water bodies, which are fundamental to sustaining life on Earth. Alongside the rise in ocean temperatures, researchers point to an accelerating rise in sea levels and continuing ocean acidification, both closely tied to the amount of heat and carbon dioxide the oceans absorb from the atmosphere.

Warmer oceans have wide-ranging consequences, from more intense and frequent marine heatwaves that can devastate coral reefs and fish populations, to changes in ocean currents that influence weather patterns far beyond the coastlines where the heat is absorbed. Rising sea levels driven partly by thermal expansion of warmer water also increase risks of coastal flooding and erosion in low-lying regions around the world.

Ocean acidification, meanwhile, occurs as seas absorb increasing amounts of carbon dioxide from the atmosphere, altering ocean chemistry in ways that can harm shell-forming organisms and disrupt marine ecosystems. Scientists have warned that the combination of warming, rising and increasingly acidic oceans poses a mounting threat to marine biodiversity and to the communities and industries that depend on healthy ocean ecosystems.

The findings add to a growing body of evidence pointing to the accelerating pace of change in the world's oceans, which researchers say will require sustained monitoring and continued efforts to curb greenhouse gas emissions in order to slow the trend.