The Global Carbon Cycle

Ocean warming is primarily caused by human activities that increase greenhouse gases in the atmosphere. Burning fossil fuels for energy and transportation, and clearing land and forests for agriculture and urban development, releases carbon dioxide, methane and other gases that trap heat, creating an energy imbalance that warms the planet. Despite progress in clean energy, growth in natural gas and oil use keeps pushing global fossil emissions up: atmospheric CO₂ concentration reached 427.49 ppm in 2025, 52% above pre-industrial levels.

The ocean has slowed the pace of atmospheric warming by absorbing enormous quantities of heat and carbon. The ocean carbon sink (its net uptake of CO₂) has accounted for roughly 29% of total emissions absorbed over the past decade, though its strength fluctuates with climate variability and is being weakened by marine heatwaves and surface warming, which reduce CO₂ solubility.

The ocean's dissolved inorganic carbon reservoir alone is over 20× every other reservoir combined, a central reason the ocean has bought the rest of the planet time.