A new international study has provided one of the most comprehensive explanations yet for the causes of global ocean expansion and rising coastlines over the past six decades. The research, published in Science Advances, shows that Earth’s oceans are rising at nearly twice the rate observed in the 1960s, confirming that climate change is accelerating the pace of sea level rise worldwide. Scientists say the findings not only improve understanding of the processes driving ocean growth but also resolve a long-standing discrepancy between observed ocean levels and the known factors contributing to them.
The study found that global ocean levels have increased by an average of 2.06 millimeters per year since 1960. However, the rate of increase has accelerated substantially in recent decades, reaching approximately 3.94 millimeters per year between 2005 and 2023. This acceleration reflects the growing influence of global warming on both ocean temperatures and the planet’s major ice reserves.
Researchers identified ocean warming as the largest contributor to sea level rise, accounting for 43 percent of the total increase since 1960. As seawater absorbs heat from the atmosphere, it expands in volume through a process known as thermal expansion. Even without adding additional water, warmer oceans occupy more space, causing sea levels to rise. This process has been a dominant factor throughout much of the historical record.
Melting ice has also become an increasingly important contributor. Mountain glaciers account for approximately 27 percent of observed ocean growth, while the Greenland Ice Sheet contributes 15 percent and the Antarctic Ice Sheet contributes 12 percent. Changes in land water storage, such as groundwater extraction and reservoir construction, account for the remaining 3 percent. The study found that while ocean warming played a leading role in earlier decades, the contribution from melting glaciers and polar ice sheets has increased significantly since the 1990s as global temperatures have continued to rise.
One of the most significant outcomes of the research is the resolution of a scientific puzzle that persisted for years. Scientists had observed a gap between measured ocean levels and estimates derived from known sources such as thermal expansion and ice melt. The new study demonstrates that advances in observational techniques and data analysis have largely closed this gap. Improvements included more accurate satellite measurements, better corrections for instrument drift, enhanced monitoring of land movement near coastal tide gauges, and refined calculations of ice loss from Greenland and Antarctica.
The findings strengthen confidence in climate models and provide greater certainty about the causes of modern sea level rise. Researchers say the improved agreement between observations and calculations confirms that current scientific understanding accurately captures the major processes affecting global ocean levels.
The study also highlights the long-term nature of the challenge. Oceans absorb and store enormous amounts of heat, responding slowly to changes in atmospheric temperatures. Similarly, glaciers and ice sheets can continue melting for decades or centuries after warming begins. Because of this climate system inertia, scientists expect sea level rise to continue for many generations, even if greenhouse gas emissions are eventually stabilized. The research underscores that rising oceans remain one of the most enduring and consequential impacts of human-driven climate change, with effects that will shape coastlines and communities around the world for centuries to come.
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