Commentary: The sea-level threat is worse than you think

Look what we have done. Let’s put this global warming and climate change thing in perspective.

For the past million years, atmospheric carbon dioxide fluctuated between 180 parts per million (ppm) and 280 ppm about every 100,000 years, and, in concert, temperature cooled and warmed and sea level went down and up 330 feet or more.

These natural changes in carbon dioxide, temperature and sea level occurred over thousands of years as Earth changed how she presented herself to the sun — cycles of a more and less circular orbit and changes in the amount and direction of the tilt of her axis to the sun.

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For the first time in the paleo-record, carbon dioxide levels have risen by more than 110 ppm and within only 100 years because of our burning fossil fuels. The overall human-generated rise in carbon dioxide from 280 to 410 ppm is more than double the 180-280 ppm post-glacial increase that drove 420 feet of sea-level rise in response to natural warming and ice melt — and it has happened 100 times faster!

Earth’s climate is now severely out of balance and will respond in unprecedented, dire and most certainly rapid ways.

Both natural climate change and the dramatic human-induced global warming is being caused by the sun’s radiation reflecting off the Earth’s surface at a longer wavelength and being caught and turned into heat by greenhouse gases, principally carbon dioxide, methane and nitrous oxide.

These extra greenhouse gases put into the atmosphere by human activities have now warmed the atmosphere by more than one degree above pre-industrial revolution levels, possibly enough to trigger the total melting of the Greenland Ice Sheet.

Carbon dioxide remains in the atmosphere a very long time, and the effects of human-induced atmospheric warming will be felt for several thousand years. Yet, if that were the whole story, it would just be a challenging matter to remove the excess greenhouse gases from the atmosphere, and the heat would quickly diminish.

Only about 2 percent of this excess heat remains in the atmosphere.

Over 93 percent of this excess global warming heat has transferred to the oceans, 2 percent has warmed the land, and about 2 percent has gone to warm and melt ice.

Our warming ocean will be causing serious climate, ice melt and sea-level changes for centuries. How do you cool down a warmed ocean?

Most disconcerting, half of the excess heat buildup in the oceans has occurred since 1997. Our still rapidly increasing greenhouse gas levels, because of rapidly increasing global population and industrialization, are making global warming more and more serious and less reversible every day we keep using fossil fuels.

Earth’s rate of global mean sea level (GMSL) rise doubled after 1930 as our warming ocean began expanding. Since 1990, we have had an additional quadrupling of the rate as accelerating polar ice melt has kicked in.

Globally, we are up to about 4.6 millimeters rise per year, a rate of 1.5 feet per century. Accelerating ice melt is now doubling this rate every seven to eight years. That will get our coasts in trouble very quickly.

South Florida’s rate of sea-level rise has been a bit faster than GMSL in the past and is predicted become significantly faster in the future.

Current federal government projections for GMSL rise, those that include accelerating polar ice melt, see a further 5 to 8.2 feet of global sea-level rise by 2100.

Because of the many accelerating ice-melt feedbacks that are observed but not in the models for these projections, it is prudent to use the higher number for planning. So, 8.2 feet of further GMSL rise this century could mean 2 feet by as early as 2046 and 4.2 feet by 2068.

Every section of coast has regional influences that add to or subtract from the GMSL rise. For South Florida, our future “total relative sea level” rise will include an addition of 15 to 20 percent from projected slowing of the Florida Current/Gulf Stream and 20 percent to 52 percent from redistribution of ocean mass as the Greenland and Antarctic ice sheets melt.

Their huge ice masses pull water toward them. As they melt and their mass diminishes, their gravitational attraction diminishes and ocean water redistributes.

This means that South Florida should add 35 percent to 72 percent additional rise to the GMSL projections. The total relative sea-level rise for South Florida by 2046 could thus be 2.7 to 3.4 feet, and within 50 years could be 5.7 to 7.2 feet. This is not an encouraging future when you look at elevation maps of South Florida or most any other coast.

It is time for all citizens, businesses and elected leaders to begin planning for the real future before us and to quickly move beyond the antiquated and harmful fossil fuel phase of the Industrial Revolution.

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