Alarming: Study Finds Highest Sea Level Rise In Last 2000 Years; Linked to Increasing Global Temperature

A conclusive study on climate and its impact on the rise of sea level is out and the results are quite grim. An international team of researchers, including many from the University of Pennsylvania, has put forward incriminating data acquired through decades that unambiguously points to a direct correlation between increase of ocean surface temperature and the rise of global sea-levels.

The Team

The study is led by Benjamin Horton, associate professor and director of Sea Level Research Lab, in collaboration with Andrew Kemp and Michael Mann, the man who first came up with the famous hockey-stick graph (see below). It is funded by the National Science Foundation among other institutes and boasts of many scientists from institutes like University of Pennsylvania, United States Geological Survey and the National Oceanic and Atmospheric Administration.

The famous Hockey Stick Graph by Michael Mann. The black line represents

This is the first complete continuous sea-level reconstruction for the past 2000 years. The trends have been compared with signs of global temperature increase and the positive correlation is too overwhelming to ignore.


The study finds that from 100 BC to 950 AD, the oceanic temperature was stable and so was the sea-level. For the next 400 years, the sea level rose by half a millimetre every year on average. This period in human history, called the Medieval Climate Anomaly, saw a steady rise in annual temperatures globally. Temperatures stayed cool and stable till the 19th century after that medieval period. However, since the late 19th century and, especially in the 20th century, sea-levels have risen on average by an alarming 2mm per year, surely one of the highest rates in the entire of Earth’s history. Again, a direct correlation with temperature rise was noted.


The team did a thorough job with the research. They used micro-fossils called foraminifera as markers. Found in sedimentary rocks, they respond in quantitatively measurable ways to change in the salinity of the water they live in. By drilling into the sedimentary rock, fossils from different ages can be studied. Bear in mind that, since, sedimentary rocks stack up in layers, drilling deeper means that we are effectively looking at older rocks a sort of geological time capsule. The samples, taken mainly from the marshes in North Carolina, can be dated by using radiocarbon dating techniques on the rocks in which it is found. A check on the dates was provided by a complimentary technique the Potassium-Argon dating method. Core samples equivalent to 2000 years were dug up.

Two typical foraminifera fossils; these are used extensively for radiocarbon dating
A typical core sample taken from sedimentary rock layers

This is much less than the core samples dug up from the Arctic, but the markers in the Arctic snow are much less useful. However, both tell essentially the same story, pointing to the same direct correlation.

The team accounted for effects of hurricanes that generally rearrange sedimentary layers by taking samples from places that face away from the sea. Hurricane imprints are easy to read, as the sedimentary rocks show unusually high amounts of sand blown in from the sea. The team also accounted for vertical land movements that will show a parallax in the sea-level rise data.

Horton says:

It’s evidence to support the obvious. The basic laws of physics say if you increase temperature, ice will melt. But what we show is how sensitive sea level is to changes in temperature

The study is co-authored by Horton, Kemp and Mann appeared in Proceeding of the National Academy of Sciences yesterday, i.e. on the 20th of June.

This study disappoints in only one respect it doesn’t predict any trend for the near future. However, climatologists are already mulling the option of extrapolating the data to see if it fits.

Kemp points out:

Scenarios of future rise are dependent upon understanding the response of sea level to climate changes. Accurate estimates of past sea-level variability provide a context for such projections


A cleavage seen in the Antarctic ice-shelf with fresh water running down into it. The people provide the scale
Is this paranoia or the future?

The Last Word

The trend is disturbing. Carbon dioxide levels are rising, undoubtedly due to human activities. Now with this study confirming the worst, nations must take the imperative to bring their individual carbon footprints out. Skeptics may object, but it will take more than mere objections and fault-finding to get around this report. Silent numbers and dumb graphs speak louder than verbose microphones.

We should better pay attention. We’ve only one planet for ourselves.

Published by

Debjyoti Bardhan

Is a science geek, currently pursuing some sort of a degree (called a PhD) in Physics at TIFR, Mumbai. An enthusiastic but useless amateur photographer, his most favourite activity is simply lazing around. He is interested in all things interesting and scientific.