A Climate Realist’s (not so) short Answers to Hard Questions About Climate Change. Question 8 (of 16) How much will the seas rise?

Justin Gillis answer to Question 8. How much will the seas rise?

“The real question is not how high, but how fast.

The ocean is rising at a rate of about a foot per century. That causes severe effects on coastlines, forcing governments and property owners to spend tens of billions of dollars fighting erosion. But if that rate continued, it would probably be manageable, experts say.

The risk is that the rate will accelerate markedly. If emissions continue unchecked, then the temperature at the Earth’s surface could soon resemble a past epoch called the Pliocene, when a great deal of ice melted and the ocean rose by something like 80 feet compared to today. A recent study found that burning all the fossil fuels in the ground would fully melt the polar ice sheets, raising the sea level by more than 160 feet over an unknown period.

With all of that said, the crucial issue is probably not how much the oceans are going to rise, but how fast. And on that point, scientists are pretty much flying blind. Their best information comes from studying Earth’s history, and it suggests that the rate can on occasion hit a foot per decade, which can probably be thought of as the worst-case scenario. A rate even half that would force rapid retreat from the coasts and, some experts think, throw human society into crisis. Even if the rise is much slower, many of the world’s great cities will flood eventually. Studies suggest that big cuts in emissions could slow the rise, buying crucial time for society to adapt to an altered coastline.”

My answer to Question 8. How much will the seas rise?

During the Pliocene epoch the water levels were about 80 feet higher than today, temperatures were 1 to 3 degree C warmer, but the CO2 level was less than 280 ppm, so there must have been another cause for the high temperatures than Carbon dioxide. My guess is that the activity of the Sun and the Milankovitch cycles triggered the meltdown of most of the Greenland and part of the Antarctic ice sheet. This is not the case now.  We are well into the bog generating phase of this interglacial period, the Minoan optimum temperature ( at 260 ppm CO2) did not trigger the ice-melt, and ever since we have been in a downward temperature trend. What is remarkable about this period is how stable sea levels have been. The ocean levels have been rising at an average rate of about one inch per century, quite different from emptying out the Baltic Ice Lake, an event that rose  Ocean levels by feet per year until it emptied out, the rest formed what is now the Baltic Sea. Coming out of the ice age rose Ocean levels about 400 feet, and then it stopped. There are places in northern Sweden where the land still rises out of the sea at about 3 feet per century. The Mid-Atlantic ridge is rising, has plenty of undersea volcanoes, about one third of all undersea volcanoes are between Jan Mayen and Svalbard. All this displaced water has to go somewhere, and so most of the rest of the world’s coastlines are experiencing rising sea levels. This is especially true for the U.S. East coast, sinking of its own. The warming of the oceans are vastly over-estimated, being confined to the surface and the upper 1000 feet, the sunlight is absorbed in the first few feet of water and there is limited and very slow mixing of deep water with surface water. But there is a temperature dependence of sea levels, the sea levels were fluctuating with temperature, as the chart to the right indicates.

Right now average ocean levels are increasing by about a foot per century, but the trend is not increasing. See Fig:

The take-home from this chart: Sea level rise has nothing to do with CO2 level rise, it is more about tectonic plates movements and what happens on the sea floor.