Is sea level rise the same everywhere around the globe?
Perhaps surprisingly, the answer is no. Tides, wind and salinity all have a local effect, though there are far larger forces at play. One of those is gravity. Waves aside, the surface of the ocean isn’t flat: variations in Earth’s gravity pull it into an uneven, constantly evolving shape. “Earth’s gravity field isn’t static in time. As mass is redistributed on the surface of Earth – from melting glaciers, say – the gravity field changes, and that affects sea surface height,” explains Jonathan Bamber, a professor of Glaciology and Earth Observation at the University of Bristol in the United Kingdom and the Technical University of Munich in Germany. Another major influence is the rotation of the planet. If you try to push over a spinning top as it rotates in place, it will resist the movement, an effect known as the conservation of angular momentum. The same thing happens on Earth – if glaciers melt, this pushes mass around the planet, and the axis must adjust to conserve momentum. As more ice melts, we are moving the axis of the planet ever so slightly. Yet even these small changes can alter the distribution of the oceans. “As Greenland and Antarctica melt, there’s a whole load of low-lying atolls in the western Pacific that are going to see the highest rates of sea level rise due to this effect,” says Bamber. Seawater also expands as it gets hotter, and shrinks as it cools. Ocean temperatures are warming all over the planet, but not in a uniform way. This also means sea level rise won’t be equal everywhere. “Thermal expansion of the oceans also seems to be amplified in the western Pacific,” notes Bamber. “So when you combine these two effects, it’s pretty bad news for the small Pacific islands.”
Calculating sea level rise around the world
In the EU-funded GlobalMass project, Bamber and colleagues tackled some of the challenges in measuring sea level rise around the globe. Using a statistically rigorous combination of satellite and in situ data, the team could piece together contemporary and future projections of sea level rise and better understand the underlying factors. Research published in the project suggests a 5 % probability that sea levels could rise by over two metres by the end of the century. This could potentially affect around 600 million people.
The tide is high
Preventing this catastrophe – or simply slowing the effects of climate change – requires drastic changes to the way we live today, says Bamber, including a rethink of our current economic systems. “To halt sea level rise, or at least the long-term accelerating trend in sea level rise, we have to go back to pre-industrial temperatures,” Bamber adds. Just one reason why the EU plans to be the first climate-neutral continent by 2050. Click here to find out more about Jonathan Bamber’s research: Attributing global sea level rise to its component parts
Keywords
GlobalMass, sea level rise, global, warming, glaciology, glaciers, mass, rotation, tides, gravity