Coastal Land Area Is Expanding So Fast That ‘Catastrophic’ Sea Level Rise Cannot Keep Up

Contrary to what would be expected with alarmingly high sea level rise rates, shorelines across the world are expanding rather than retreating into the sea.

A few months ago we highlighted an analysis of the post-2000 net expansion (from 1007.60 km² to 1069.35 km², or +6.1%) in coastal land area for 221 Pacific and Indian Ocean islands (Holdaway et al., 2021).

Over half of the net 21st century growth (39 km² of 62 km²) for these islands occurred in a span of just four years: 2013 to 2017.

Image Source: Holdaway et al., 2021

Notice the rapid shoreline changes in these satellite images of the coast of Lagos, Nigeria (Adeaga et al., 2021). The first (b) is from 2006. The second (c) is 2012. The last image (f) is 2020.

Between 2001 and 2020 the average regional net shoreline growth rate was +0.93 m/year. One area – Victorian Island – has had a mean shoreline change rate of +6.24 m/year.

Image Source: Adeaga et al., 2021

The current shoreline for Salerno City, southern Italy, has expanded seawards rather rapidly in recent centuries (Amato et al., 2020). If we track the relative location of the red “GS” dot from the below images we see that the 17th to 18th centuries (0.3 ka) had a shoreline >250 m further landward than 2016.

Image Source: Amato et al., 2020

During Roman times (~2200-1600 years ago), CO2 levels were about 265 ppm. Ephesus was then a thriving seaport city situated on the Aegean Sea.

Sea levels have fallen ~2-3 m in recent millennia, as more water is trapped on land as ice today.

The Ephesus harbor remains are now 9 km from the coast.

Image Source: ephesus.us and David Noel, Australia

A new study (Desruelles et al., 2021) details the history of Rue, a sea harbor town in the 12th and 13th centuries.

Today Rue sits ~6 km from the sea coast.

Evidence for the presence of Late Holocene dunes and sand can be found spanning from the Rue site to the current coastline. A 1579 map still had Rue nearly bordering the sea, suggesting that the retreat of the sea waters has been relatively recent.

Image Source: Desruelles et al., 2021

Scientists (Lee et al., 2021) have studied the history of Holocene coastal flooding along the southern part of the Korean Peninsula. Judging from the distance (km) metric in the legend, the study site (red circle) is located at least 50 km inland from today’s coast.

The authors determined sea levels during the Early to Middle Holocene (peaking ~6,000 years ago) were high enough that marine species and “abundant shell fragments” can be found at the study site, which means “sea levels reached the vicinity of the study area during this period.”

Image Source: Lee et al., 2021

Italy’s famous leaning-tower city, Pisa, used to be a bustling sea port just ~3,300 years ago. That was when sea levels were much higher than they are today.

As the seas retreated over the next millennia, Pisa was left sitting almost 4 km from the sea coast during the Roman Warm Period.

Today Pisa is located 9.7 km from the coast.

Image Source: romanports.org