The prestigious journal Nature is publishing important new research on “Rapid sea-level rise and reef back-stepping at the close of the last interglacial highstand” (subs. req’d, abstract below). As Nature explains in a summary and author interview (subs. req’d):
Some consequences of climate change are already unfolding. Glaciers and ice sheets are melting, and sea levels are rising as a result. However, scientists aren’t certain by how much the rate of sea-level rise might accelerate; current predictions for increases until 2100 range from 0.3 centimetres to 1.4 centimetres per year. But Paul Blanchon, a geoscientist at the National Autonomous University of Mexico in Cancºn, and his colleagues have learned that a sudden, catastrophic increase of more than 5 centimetres per year over a 50-year stretch is possible. On page 881, they describe their discovery that a sea-level jump of 2-3 metres already happened about 121,000 years ago. Blanchon tells Nature how and why it could recur [see below].
In other words, the Nature study says that during the during the last interglacial (the Eemian) evidence now suggests sea levels rose 20 inches per decade for five straight decades — a roughly 8-foot rise in a half century.
The Eemian was some 2°C warmer than current global temperatures — we will exceed that over most of the second half of this century on our current emissions path (see “Intro to global warming impacts“).
The authors conclude bluntly:
In our warming world, the implications of a rapid, metre-scale sea-level jump late during the last interglacial are clear for both future ice-sheet stability and reef development. Given the dramatic disintegration of ice shelves and discovery of rapid ice loss from both the Antarctic and Greenland ice sheets, the potential for sustained rapid ice loss and catastrophic sea-level rise in the near future is confirmed by our discovery of sea-level instability at the close of the last interglacial.
This research amplifies the findings in a number of recent studies — and warnings from leading climate scientists — that sea level rise can occur much more rapidly than scientists thought just a few years ago:
- US Geological Survey stunner: Sea-level rise in 2100 will likely “substantially exceed” IPCC projections
- Startling new sea level rise research: “Most likely” 0.8 to 2.0 meters by 2100
- Sea levels may rise 5 feet by 2100
- Inundated with Information on Sea Level Rise
- Amazing AP article on sea level rise
- Report from AGU meeting: One meter sea level rise by 2100 “very likely” even if warming stops?
And remember, many of those studies and estimates were made before the new recent projects that temperature rise this century may be 4°C to 5°C or more.
If sea levels were even 3 feet higher in 2100 (let alone 5 or higher) and rising 1 to 2 inches a year at that point, it would be the single greatest preventable catastrophe in human history. We cannot let it happen.
Here is an excerpt from the Blanchon interview:
How did you find out that sea levels had risen so quickly in the past?
We were studying fossil reefs along the Yucat¡n peninsula in eastern Mexico, looking for interruptions in the reefs’ development, when we found two reef crests. One crest was about three metres above the current sea level, the other six. Some event had clearly disrupted their growth, killing the lower reef first and, within 50 years, allowing the higher one to develop into territory that is now farther inland. One possible cause of such disruption is an earthquake, but we know the peninsula was stable in the reefs’ lifetimes. The only other possibility is a rapid sea-level jump of two to three metres, which would essentially have drowned the lower reef.
Did you have to dive to the ocean floor to study the fossil reefs?
No, a theme park has been excavated in the middle of these reefs, which are on land south of Playa del Carmen. There’s no other place in the world where reefs of this age are so exposed. From the excavations, we were able to reconstruct the reef’s internal structure in three dimensions….
What do your results mean for sea-level rises in the future?
This earlier ice-sheet collapse happened during an interglacial, when it was warm and there wasn’t a lot of ice around “” just as it is on Earth today. We’re assuming rapid ice loss from an ice sheet produced the jump in sea level, because it’s the only known process that could generate such a rapid increase. This could happen again.
You can read more in Andy Revkin’s NYT piece, where he characteristically quotes some researchers who believe that the authors have not made their case:
To determine the pace of sea-level rise in that period, Dr. Blanchon charted patterns of coral revealed in excavations at the resort. He said his work revealed a clear point where an existing reef died as the sea rose too fast for coral organisms to build their foundation up toward the sea surface. Once the sea level stabilized again, the same group of corals grew once more, but farther inland and up to 10 feet higher in elevation, a process known to geologists as backstepping.
Such an abrupt change from stable coral growth to death and a sudden upward and inland shift of a reef could only happen because of a sudden change in sea level, he said.
But in interviews and e-mail messages, three researchers who focus on coral and climate said that while such a rapid rise in seas in that era cannot be ruled out, the paper did not prove its case.
Daniel R. Muhs, a United States Geological Survey scientist who studies coasts for clues to past sea level, cited a lack of precise dating of the two reef sections. William Thompson, a coral specialist at the Woods Hole Oceanographic Institute, agreed, saying that given the importance of the conclusion, Dr. Blanchon interpreted the physical features without sufficient corroborating evidence.
[Note to Andy: Where is the third critic?]
But Dr. Blanchon maintains that the work will hold up, saying the signs of abrupt change are etched in the rock for everyone to examine.
It is an interesting journalistic question as to whether straight science reporting on a new study needs such “balance.” After all, the article passed Nature‘s rigorous peer review process. That suggests the experts Nature chose to review it thought it was both accurate and important.
I would say it is perfectly legitimate to quote one or two scientists who question the results — but only if your story also points out that a number of other studies using very different methods have projected rates of sea level rise that are quite comparable (see links above).
Indeed, as I’ve previously noted, in 2007 a Nature Geoscience study looked at the last interglacial period (the Eemian, about 120,000 years ago) “” the last time the planet was as warm as it soon will be again. That study found seas rose 1.6 meters (5 feet) per century “when the global mean temperature was 2 °C higher than today,” a rather mild version of where we are headed in the second half of this century.
So until and unless the journal or the authors publish a correction, this study serves as one more important warning from Nature and from little ‘n’ nature that we are risking unmitigated catastrophe if we don’t cuts emissions sharply and soon.