As I mentioned in Global Warming V, climate scientists published a major review and additional new work about sea level rise. Here’s the excellent New York Times article about it, and here’s an informative blog about these results written by one of the scientists. I showed a couple of the graphs from Dr. Rahmstorf’s blog post to my Physics 125 students for a recent Science in the News. We don’t get to climate change in the book for several weeks, but along with that temperature graph for 2015 in Tampa, sea level rise is directly relevant to my students. Our classroom is about 10 feet above the normal level of the Hillsborough River flowing about 50 meters away.
Here’s what Dr. Rahmstorf calls “the main result.”
Fig. 1 Reconstruction of the global sea-level evolution based on proxy data from different parts of the world. The red line at the end (not included in the paper) illustrates the further global increase since 2000 by 5-6 cm from satellite data.
He cautions us that there may be a slow long term linear trend that he and his colleagues cannot identify or remove. If this trend were known and accounted for there might be a tilt in the data, one way or the other. Thus, he suggests that the level shown in the graph, say for the year 400 CE, about 10 cm, should not be directly compared to the 10 cm level 16 centuries later when the level passed 10 cm going upward around 1950 or so. Within a few centuries this trend, however, would not skew the results. Thus, from these data we can see that in the past century or so the sea level is rising more rapidly and more overall than in any earlier sea level changes, going back 2500 years. Further, we can see that there is no sign that the present rise is reaching a maximum. Indeed, he has added a few years’ data from the 21st century, in red, which continues the steep rise. Of course, a professional researcher has put in an error range, and the arbitrary zero is there for us to see. You can read the details in the blog post.
I’ll just say that 500 BCE is the time of the destruction of the first Jewish Temple in Jerusalem, the time of the Persian invasions of Greece, a time when the Roman Republic was just one small state among many warring groups in Italy. The 20th century’s sea level change is unprecedented during this time.
Of course, 10 cm or 20 cm (4 or 8 inches) doesn’t seem like much. It just adds as small amount to the base level from which, say, a hurricane storm surge and high tide add their damage. Not only is the U of Tampa, and all of downtown Tampa within a dozen feet of sea level, but so is Governor Scott’s beach house in Naples, and, as we saw with Hurricane Sandy, Manhattan. It seems clear that the 10 or 20 cm visible in these data will not be the end of the sea level rise in the 21st century. Well, Governor Scott and I are old guys, but I wonder that he has so little concern for our children and grand-children. The blog shows the results of studies of likely 21st century sea level rise under various possible warming futures. Fifty cm is likely, more than a hundred cm is possible.
Dr. Rahmstorf describes an important paper by well-known researchers in which they attempt to predict likely outcomes 10,000 years into the future! Here’s the figure from that paper that he posted in his blog.
Fig. 5 From the Ice Age to the Anthropocene: the last 20,000 and the next 10,000 years of sea level, by Clark et al. 2016. The vertical scale is measured here not in cm but in meters: at the height of the last Ice Age, at the start of the curve, global sea level was about 125 meters lower than today. Due to our greenhouse gas emissions we are currently setting in motion a sea-level rise of 25 to 50 meters above present levels. The small inset maps show the ice cover on Greenland and Antarctica. The lower curves give the rate of sea-level rise in meters per century.
Pay attention! The vertical axis is in meters. The Pleistocene was the last ice age. So much water was locked in the immense continental glaciers that the sea was about 125 or 130 meters lower than today. That is, about 400 feet lower. The Florida peninsula is flat, flat, flat. The highest things in Tampa are the freeway overpasses and the tall downtown buildings. The flatness extends under the Gulf of Mexico and into the Atlantic. Back in those days, Florida was much wider than it is today. Longer too. As this ice melted over about 10,000 years, the sea rose to its present levels, the Holocene. Notice that these researchers also label the future with the new name Anthropocene. Now we are the dominant force defining the Earth’s conditions, and these are so distinct from the past that scholars have put forward a new name.
As the Earth emerged from the Ice Age, humanity emerged from its hunter-gatherer life and began settling into agricultural communities. During the past 6 or 7000 years, as you can see from the lower graph, the sea level has been mostly constant. What was going on 6000 or 7000 years ago? 4000 BCE or 5000 BCE? The first pyramids. The first stones at Stonehenge. From that time until now, humans have created all of our civilizations. Of course, we’ve taken the opportunity to do plenty of uncivilized things too.
Now we are blasting ourselves and the rest of the planet into a radically new regime. Even if we manage to stop carbon dioxide emissions soon, the temperature will continue to warm for decades or centuries, and the ice will of Greenland and Antarctica will continue to melt. The arctic sea ice will also melt, but it is already floating, so that will not change the sea level much. Melting the arctic sea ice will have other unpredictable and bad effects though.
The maps in the chart show present day ice cover for Greenland and for Antarctica now and far in the future. The researchers, as you can see, consider various possible scenarios, but all of them have major long term effects.
Miami is going underwater probably this century. Even now sea water seeps out of the ground, flooding low lying streets and lawns. The porous Florida limestone means that dikes and sea walls will be useless.
New York, Boston, Baltimore, San Francisco, and other important US cities will drown under 2 or 3 meters of sea level rise, which is possible by during the 22nd century. Entire populous nations, such as Bangladesh, will be under 20 or 40 feet of sea water. The entire country. Tens of millions of people will have to find some other place to live. This is hundreds of times more people than today’s Syrian refugees causing so much trouble for other nations.
I could go on about this. This entire matter, global warming, is an elementary consequence of the 1st Law of Thermodynamics, the Conservation of Energy. And an entire major political party denies all of this, and attributes these results to corruption and conspiracy.