The Fruits of Civilization (67-14) Rising Sea Level

Deglaciation & Rising Sea Level

It takes sea-level rise a very long time to react — on the order of centuries. It’s like heating a pot of water on the stove: it doesn’t boil for quite a while after the heat is turned on, but then it will continue to boil as long as the heat persists. Once carbon is in the atmosphere, it will stay there for tens or hundreds of thousands of years, and the warming, as well as the higher seas, will remain. ~ American geoscientist Peter Clark

Even if we were to freeze greenhouse gases at current levels, the sea would actually continue to warm for centuries and millennia, and as they continue to warm and expand the sea levels will continue to rise. ~ Gregory Johnson

Since glaciers and ice caps are masses of land-based frozen water, their melting and runoff into the oceans causes sea levels to rise. In contrast, because sea ice formed in the ocean and floats there, its loss would be relatively insignificant to sea-level rise.

Even without deglaciation, sea levels would rise simply from the waters becoming warmer. Matter, including H2O, expands when heated. Warming invokes thermal expansion.

The Last Glacial Maximum was the last period of severe glaciation. Ice sheets reached their maximum 26.5 thousand years ago (tya). Deglaciation commenced in the northern hemisphere 19 tya. Antarctica started shedding ice 14.5 tya, provoking an abrupt rise in sea levels. At the time, vast ice sheets covered much of North America, northern Europe, and Asia.

Ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. ~ James Hansen et al

Over the past century, sea level rose at an average rate of 1.5 mm, increasing to 3.2 mm a year 1990–2010. The rise is accelerating, as the large ice masses of the world melt. Artic ice and the glaciers of the Himalayas will be gone well before the end of the century; perhaps even Antarctica’s ice too, as the rate of ice decline there since 2014 has been precipitous.

In the 1st decade of the 21st century, changes in the global water cycle more than offset the terrestrial losses from human extraction. The land has been acting as a sponge: soaking up an extra 2.9 trillion tonnes of water in soils, lakes, and underground aquifers. This has temporarily slowed sea-level rise by 20%.

Climate-driven land water storage uptake is of opposite sign and of magnitude comparable with ice losses from glaciers and ice sheets and nearly twice as large as mass losses from direct human-driven changes in land water storage. ~ American hydrologist J.T. Reager et al

How long the land has been soaking up extra water is not known. But one thing is certain: once the crust is saturated, sea-level rise will quicken.

Sea-level rise is going to continue to accelerate if there’s further warming, which inevitably there will be. ~ German ocean physicist Stefan Rahmstorf

◊ ◊ ◊

2016 estimates foretold global sea-level rise close to 3 meters by 2100: more than double the estimated rise in 2006, and 25% more than in 2012. Revisions to sea-level rise in the geological near-term keep going up. In 2017, the prediction was over 3 meters: up nearly 20% from just a year earlier.

Changes in ocean currents will affect the way that seawater is distributed throughout the world. Further, melting glaciers are likely to affect Earth’s gravitational field and even its rotation, which will also alter current flows.

Sea-level rise will be more pronounced in certain areas, such as on the east coast of North America.

Continued warming assures sea-level rise for centuries to come.

Sea level rise has the potential to affect millions of people living in low-lying coastal regions, particularly the inhabitants of megacities on coasts around the world, and those living on deltas of major rivers and small island nations. ~ Australian climatologist John Church in 2004

Entire populations of cities will eventually have to move. ~ Peter Clark

Measures to deal with sea-level rise take a lot of time and sustained political will. Britain erected a storm surge barrier on the Thames River after a catastrophic 1953 storm in which over 2,000 people perished; but it took almost 30 to do so, and that was fast compared to similar construction projects.