The two invisible forces driving our rising global sea levels
In short: While melting glaciers grab the headlines, a silent physical process is also pushing ocean levels upward. Understanding the dual mechanics of sea level rise is essential for predicting the future of our coastal populations and the stability of our global climate.
Global sea level rise is driven by two primary mechanisms, both linked to a warming planet. The first is the addition of fresh water into the oceans from melting land ice, specifically from mountain glaciers and the massive ice sheets of Greenland and West Antarctica. The second is thermal expansion: as ocean temperatures rise, the seawater itself expands, occupying more volume.
Currently, the contribution of melting land ice is the dominant driver, accounting for approximately two-to-thirds of the rise, while ocean warming contributes the remaining one-third. Satellite measurements have documented a significant upward trend, showing that global sea levels have risen by roughly 3.6 inches (91 millimeters) since 1993.
However, the ocean's surface is not rising uniformly. While long-term trends show a global increase, local changes vary based on ocean currents and the sinking or rising of coastal land. In some specific locations, particularly those near melting glaciers, sea levels may even appear to be dropping. Furthermore, the data reflects a seasonal cycle; as moisture moves between land and sea via the water cycle, ocean levels fluctuate annually, often following the patterns of the Northern Hemisphere's seasons.
To track these shifts, NASA utilizes a sophisticated network of tools, including satellites, lasers, and radar. Missions like Jason-3 and the Sentinel-6 Michael Freilich provide the continuity needed to observe these changes over decades, while the SWOT mission aims to provide the first global survey of Earth's surface water topography.
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Sources
- Summary by Intellect · source: Science Bulletins: Melting Ice, Rising Seas
- Also: Sea Level - Earth Indicator - NASA Science
- Also: NASA Scientific Visualization Studio | Melting Ice, Rising Seas
- Also: gpm.nasa.gov — Melting Ice, Rising Seas | Precipitation Education
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