Responding to the Green Man‘s post regarding massive erosion of the Alaskan coast, a visitor named Tomas has claimed that “sea levels are rising to about where they were roughly two thousand years ago.” Challenged to provide any peer-reviewed scientific literature supporting that claim, Tomas has been unable or unwilling to do so.
I’ve gotten tired of waiting, so I’ve taken a peek into the literature myself. One of the most interesting, clever and most-cited pieces of peer-reviewed research on historical sea level change is a 2004 paper by Kurt Lambeck and Italian associates. Lambeck et al use ancient Roman piscinae (fish ponds) from approximately 2000 years ago to reconstruct sea level change. These ancient fish ponds are important because in order to work (see also here and here for additional reporting of the results), their sluice gates must be placed precisely at sea level. Working at 8 different sites (see map at right) and accounting for tectonic shifts, Lambeck et al produce the following estimates of sea level change from approx. 2000 years ago to the present day:
The final section of Lambeck et al’s 2004 paper examines more recent tidal gauge measurements in the same area and, comparing the rate of change in sea level according to tidal gauges with the longer-term rate of change according to the placement of the Roman fish ponds, concludes that sea-level saw a significant acceleration in its rate of rise in the late 19th or early 20th Century. A review of the scientific literature on historical sea-level rise by Roland Gehrels of the University of Plymouth reveals that global tide gauge data and microfossil reconstructions at other sites are in agreement with Lambeck’s finding of accelerated sea-level rises beginning in the late 19th to early 20th Century.
“Eh, scientists – wadda they know?”
Wait, you’re saying sea level was LOWER 2,000 years ago? Just like all the scientists say?
Actually, I was very careful NOT to say that. Lambeck et al take care in their paper to talk about post-glacial rebound and tectonic shift, taking both into account, and that’s not captured fully in the second graphic you see there. After they take those local geographic tendencies into account, the amount of sea level change apart from that is wholly accounted for by the accelerated changes that take place after the end of the 19th Century.
It’s a complicated empirical account, and I encourage you to read the paper to “grok” it fully.