I have always felt that sea level rise would be quicker and higher than my colleagues in climate science have suggested. My reasoning for that is simple. Sea level rise has in the past not followed overall climate change in a perfectly simple manner such that the present era has lower sea levels than it should. When this was noticed in the mid 20th century up through the 1970s, in the form of high wave cut benches along various rocky shore lines, the explanations usually invoked moving land masses, such as a continent buoying upwards as it eroded, so the same sea level would cut benches that were higher and higher the farther back in time you go. And, that probably happens to some extent. But it turns out that the amount of ice trapped in continental glaciers in the northern and southern hemispheres is probably more than it “should” be given current conditions.
(I should note that paleontologist colleagues that I’ve discussed this with tend to think similarly.)
This is not hard to imagine. I can offer a very over-simplifed meteorological model to help see how this may be the case. (We’ve discussed this before on this blog.) The equator gets more sun than the rest of the planet per unit surface area because the earth is a ball. This extra energy sets up a giant rotating donut shaped mass of air on each side of the “equator” (not the exact equator) which involves air moving upwards, then moving away from the equator, then cooling and dropping down and then getting sucked back into the vortex-like rotating donut again. (On the way up the air lost much of it’s moisture; thus, tropical rainforests.)
This giant rotating donut sets up a counter-rotating donut away from the equator both to the north and the south. This secondary donut has the property of having much dryer air, so instead of lots of rain forming along it’s circular length, you get dryer conditions along its circular length. Go look at a map of the world. Find all of the southern arid regions. Note that they line up east-west wise with each other. Now find all the northern arid regions. Same thing. (There are some exceptions, ignore them. Later, for extra credit, you can work out explanations for them.) At first you might think that these arid bands that encircle the earth are at different distances from the poles, but that is because the map you are looking at cuts off the south pole, most likely. Look at the latitudes themselves; both the northern and southern hemispheres have a dry band in the same position in relation to the equator.
North and south of this band, another rotating donut exists, although at this point the donut is very much a theory that occasionally manifests itself because as you get farther from the poles this whole donut thing breaks down. And then there is potentially another donut thing, maybe more like a fritter at this point, around the poles.
Remember last winter, when it was really really cold some places and stayed warm some places, thus causing great confusion? The US was warm and Europe was cold. Well, that is a falsehood. What really happened, is that in the Northern Hemisphere, there was a stark break between warmish and cold air, and all those whingy European cities (“oh, it’s so cold here”) are north of that division, and all those drippy American cities (“hey, were’s our damn snow!”) are south of that division. What happened that year is that the donuts got their ducks in a row more than usual for a little while, and made a sharper distinction between bands around the earth.
Think about it this way: Imagine that there were no ocean currents, and that all these air-donuts were very stable. If you let “air coloring” (like food coloring but for air) into the atmosphere at various points from the equator towards the poles, and got in a space ship and went really far out and looked back at the earth, it would look like those big planets with the bands around them (i.e., Jupiter or Saturn). Sort of. The Earth, in fact, has bands. It is just that the primary visible tings in the bands are water vapor (white) and dust (light brown), and the bands are poorly organized except along the equator. This, and the fact that the bands are not well organized makes it difficult to find them. But they are there.
This picture shows how the donuts operate in cross section:
And here is a picture of the earth that kinda shows the bands, if you kinda squint and look closely:
Most of the year-round ice on the planet is in the farthest zones to the north and to the south. If for a period of time, the giant rotating donut thing completely went away everywhere except at the equator (where it can’t go away) the gradient of heat from equator to pole would be smooth, and during the summer in a given hemisphere, it may be quite warm far from the equator. If, on the other hand, the heat is trapped in well formed rotating donut configurations, or for some other reason heat does not get to the distal regions of the planet, then the farthest zones will be relatively cold.
That first scenario appears to be what was happening during the last interglacial, when there was less Carbon in the atmosphere than today, but sea levels were higher. At present, however, the distal regions seem to be cooler than they should be.
However, it appears that global warming is taking care of that. The donuts (and other atmospheric circulation features) are doing something different, or the ocean is storing and moving heat around differently, or both. We may be shifting from a certain pattern whereby the topics were very tropical and the polar regions were very polar, through a period of a lot of crazy changes back and forth, to a period where the polar region will very quicly warm up.
And big whopping amounts of ice melt and sea levels go up.
If this is true, then we should expect some much larger than generally predicted melting of continental glacial ice. And, in fact, we are seeing that across the arctic over the last few years, and right now, especailly in Greenland.
For several days this month, Greenland’s surface ice cover melted over a larger area than at any time in more than 30 years of satellite observations. Nearly the entire ice cover of Greenland, from its thin, low-lying coastal edges to its 2-mile-thick (3.2-kilometer) center, experienced some degree of melting at its surface, according to measurements from three independent satellites analyzed by NASA and university scientists.
On average in the summer, about half of the surface of Greenland’s ice sheet naturally melts. At high elevations, most of that melt water quickly refreezes in place. Near the coast, some of the melt water is retained by the ice sheet, and the rest is lost to the ocean. But this year the extent of ice melting at or near the surface jumped dramatically. According to satellite data, an estimated 97 percent of the ice sheet surface thawed at some point in mid-July.
Just to be clear, according to this report from NASA, about twice the normal area has experienced melting. Measurements of the effects of volume are not yet completed. We don’t know what the total amount of Greenland Ice Sheet will be added to the ocean this summer, but it is likely to be very much more than predicted.
This extreme melt event coincided with an unusually strong ridge of warm air, or a heat dome, over Greenland. The ridge was one of a series that has dominated Greenland’s weather since the end of May. “Each successive ridge has been stronger than the previous one,” said Mote. This latest heat dome started to move over Greenland on July 8, and then parked itself over the ice sheet about three days later. By July 16, it had begun to dissipate.
Where does the heat in these “heat domes” come from? Well, the sun shining on everywhere, but mostly the climatological equator.
This sort of widespread melting in Greenland seems to come along now and then, almost periodically, possibly in cycles of a century and a half or so. Therefore, we will be able to watch the Climate Change Denialists claim that this is totally normal variation. However, as we have discussed many times, the short and medium term climate “cycles” (or, sometimes, just “variation”) occur all the time but on a substrate of physical properties of the air and ocean. The air has more and more CO2 in it, and thus can retain more of the sun’s energy for longer, and the ocean is slowly heating up, so over time it takes less heat out of the air (all else being equal) and replenishes atmospheric heat when it drops.
Some have estimated that the Greenland Ice sheet can mostly melt off if there is enough Carbon in the atmosphere. If it did, sea levels would go up about 6 or 7 meters. During the last inter-glacial, sea levels were not THAT much higher than they are now, but they were close. Between the Antarctic and Greenland, there’s plenty of ice to convert to sea. I am concerned that melting conditions in Greenland could cause a lot of that ice to become sea water in a much shorter period of time than current, in my view conservative, predictions suggest. If something similar happens in the Antarctic … a wider and more even spread of warmth in the Southern Hemisphere most years … than there would be more than enough melt-water to produce surprising and catastrophic results.