global sea level rise
Areas that would be affected by a six-metre sea level riseNASA

The ice sheets might be more resilient than we previously thought, but their new global sea level predictions would still see New York, Miami and New Orleans submerged if current melt rates continue, scientists have said. The team from Stanford University were reassessing current models that show global sea level rise as a result of the melting ice sheets.

Currently, scientist at the Intergovernmental Panel on Climate Change (IPCC) use the mid-Pliocene warm period to create computer models for global sea level rise projections. This was the last time in Earth's history (around three million years ago) that atmospheric carbon dioxide levels were close to what they are today.

Matthew Winnick, author of the study published in the journal Geology, said: "The Pliocene is an important analogue for today's planet not only because of the related greenhouse gas concentrations, but because the continents were roughly where they are today, meaning ocean and climate circulation patterns are comparable."

Previously, scientists have used oxygen isotope records to look at the volume of Earth's ice sheets during the mid-Pliocene period and work out sea level – models of ice sheet meltwater suggest sea level was probably between 82 to 98 feet (25 to 30 metres) higher than it is today. This would mean New York would eventually be 50ft underwater.

New York Skyline WIthout the World Trade Center
New York would still be submerged if global sea levels rose by 30 to 44 feet Reuters/Ray Stubblebine

However, the researchers said these findings assume that the Antarctic ice of the Pliocene had the same isotopic composition as it does now. After reassessing and refining geochemical fingerprints and extending analysis to include ice sheet models, the authors found global sea level of the Pliocene was likely 30 to 44 feet (nine to 13.5m) higher than today's levels. While this is significantly lower than previous estimates, it would still be enough to inundate Miami, New Orleans and New York City.

Winnick said: "Our results are tentatively good news. They suggest that global sea level is less sensitive to high atmospheric carbon dioxide concentrations than previously thought. In particular, we argue that this is due to the stability of the East Antarctic Ice Sheet, which might be more resilient than previous studies have suggested."

However, they also said their results should not necessarily be applied to Earth now – ice sheets normally take hundreds if not thousands of years to respond to increasing CO2, so what will happen over shorter time scales is difficult to say: "Add that to the fact that CO2 levels were relatively consistent in the Pliocene, and we're increasing them much more rapidly today, and it really highlights the importance of understanding how sea level responds to rising temperatures," Winnick said. "Estimates of Pliocene sea level might provide a powerful tool for testing the ability of our ice sheet models to predict future changes in sea level."