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 328 feet (100 meters) 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, more and less tilt of the axis, and shifting direction of tilt to the sun.
For the first time in the paleo-record, carbon dioxide levels have risen by more than 110 ppm and within the last 100 years because of our burning fossil fuels (half of the rise occurred in the last 30 years). This overall human-generated rise in carbon dioxide from 280 to 410 ppm is more than double the 180-280 ppm post-glacial increase which drove the 420 feet (128 meters) of sea-level rise in response to natural warming and ice melt – and it has happened 100 times faster!
There is no precedent for this rapidity of change. The unprecedented rate and degree of human-caused carbon dioxide increase and warming should serve as a warning. The Earth is now severely out of balance and will respond in unprecedented, dire, and most certainly rapid ways.
Global warming is a warming atmosphere transferring its heat to the oceans. Both natural climate change and dramatic human-induced global warming is being caused by the Sun’s radiation reflecting back off the Earth’s surface at a longer wavelength and that reflected radiation being caught and turned into heat by greenhouse gases.
The extra greenhouse gases we have put into the atmosphere by human activities have now warmed the atmosphere by more than one degree above pre-industrial revolution levels. That may not sound like much, but the United Nations Intergovernmental Panel on Climate Change (IPCC) says that one degree may be enough to trigger the total melting of the Greenland Ice Sheet.
These greenhouse gases are principally carbon dioxide, methane, and nitrous oxide. Carbon dioxide has a very long residence time in the atmosphere, and the effects of human-induced atmospheric warming will be felt for at least several thousand years. Yet, if that was 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.
The problem is that only about 2 percent of this excess heat remains in the atmosphere, according to a 2014 IPCC report. It was the warming of this atmospheric 2 percent that was being discussed at the Paris talks in 2015.
Over 93 per cent 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. Ocean water has the ability to take in, hold, and transport an enormous amount of heat.
This means that our warmed ocean will be causing serious climate change, 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. In other words, in 1997 we only had about half the problem we have today. Our still rapidly increasing greenhouse gas levels, because of rapidly increasing global population and industrialization and burning of fossil fuels, are making global warming more and more serious and less and less reversible every day we put off stopping the use of 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.
So globally we are up to about 4.6 millimeters rise per year, a rate of 1.5 feet (46 centimeters) per century. The problem is that this rate is now doubling every seven to eight years, and that will get our coasts in trouble very quickly. South Florida’s rate of sea-level rise has been a bit faster than the global mean in the past. We have had a 12 inch (29.7 cm) rise since 1930 versus 8 inches (20.5 cm) globally, and our rise is predicted to become significantly faster than the global mean in the future.
Current federal government projections for GMSL rise, those that include accelerating ice melt In Greenland and Antarctica, see a further 5 to 8.2 feet (1. 5 to 2.5 meters) 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 (2.5 meters) of further sea-level rise this century could mean a 2 foot (0.6 meters) rise by as early as 2046 and 4.2 feet (1.3 meters) 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 percent to 20 percent from projected slowing of the Florida Current/Gulf Stream and of 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. Neither of these numbers is trivial.
These project that we should add 35 percent to 72 percent additional rise for our area to the GMSL projections. The total relative sea-level rise for South Florida by 2046 could thus be 2 feet (60 cm) GMSL plus 0.7 to 1.4 feet (0.2-0.4 meters) for a total of 2.7 feet to 3.4 feet (0.8-1.0 meters).
Within 50 years we could see a total of 5.7 to 7.2 feet (1.7.-2.2 meters) with the regional influences added in. This is not an encouraging future when you look at the elevation maps of South Florida or of most any other coastal area.
For Galveston to the Mississippi Delta, there is also an addition from subsidence of about 2 feet (60 cm) per century. For Virginia and North Carolina there is also an addition from regional subsidence of nearly 1 foot (30 cm) per century.
The reality of accelerating rates of sea-level rise is becoming increasingly dire and urgently needs to be addressed both locally and globally.
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.
Harold R. Wanless is a Professor in the Department of Geography and Regional Studies at the University of Miami.
“The Invading Sea” is a collaboration of four South Florida media organizations — the South Florida Sun Sentinel, Miami Herald, Palm Beach Post and WLRN Public Media.
