Sea level rise is one of the most important impacts of climate change, and I’m sure every reader of these letters has an interest in its future development. All kinds of widely varied projections have been made for this century, which can only lead to confusion. Which of these, if any, are the most reliable? I keep looking for trustworthy sources. This morning my email contained a posting from a retired climate scientist who goes by the name of “Tamino.” Tamino is a much-respected expert in statistical analysis, and he also has a deep interest in sea level rise. He is quite adept at locating the best available sources of data to work with. In today’s blog he analyzes data derived from a study published in August by the prestigious Nature journal. We don’t have open access to the study, but this link contains information about the authors, references, sources of data and so on, plus the abstract: https://www.nature.com/articles/s41586-020-2591-3.
Now for Tamino’s post, which deserves a thorough reading: https://tamino.wordpress.com/2021/12/10/big-change-in-sea-level-rise/. It begins with a chart showing the trend of sea level rise since 1900, based on data taken from the Frederikse study in Nature, which I am taking the liberty of reposting in order to make clear the prominence of the trend of acceleration. Acceleration, if it continues, is the one big thing we have to worry about, and Tamino devotes most of his attention here to studying the possible means and rate of continuation:
It’s all explained using additional charts he has constructed which bring a close focus on the differences in varying sources of increase. Some of these are quite slow and steady, making a regular contribution but posing no great danger of accelerating. Greenland is a bigger risk, and then there is Antarctica, which has by far the greatest store of ice that could be melted. Antarctica remained almost perfectly stable until about 1990, but then it succumbed to change. Here is what the change looks like when subjected to statistical analysis:
Before 1990 Antarctica’s contribution to sea level rise was stuck at a minuscule amount of about 0.06 millimeters per year. In the following decade, by my reading, that number rose to an average of about 0.13mm per year, followed by 0.27mm and 0.55mm in the first two decades of this century. Here is how Tamino describes the trend: “When the rates at which ice is discharged double or triple, if that happens in enough places — and especially in east Antarctica — the rate of sea level rise could become terrifyingly high. Imagine 30 mm/yr — six times the present rate — more than an inch per year. That’s 3 meters per century, and 3 meters is about 10 feet so goodbye, Miami. Goodbye, New Orleans. Goodbye, a lot of places.”
Since 1990 the Antarctic melt rate, as measured by the Frederikse team, has doubled in each of the succeeding three decades, creating a total of only about fwo-tenths of an inch (5.5mm) for the last full decade. If the doubling pace is continued for four more decades we would see about 16 times that much, or around three inches, during the decade of the ’50s. This certainly is plausible, but still not terribly frightening. The remainder of the century is the critical time period as far as the doubling rate is concerned, giving real meaning to the word “collapse” that we sometimes hear. The decade of the ’90s would end up with a rise of about four feet. That’s truly an extreme figure, but not necessarily implausible according to some estimates. All we know for sure is that a sleeping giant has been awakened, and is very angry.
Carl