Warming Oceans Could Drive Antarctic Ice Sheet Collapse, Sea Level Rise

The study took a modeling approach to gather best estimates of the planetary influences underlying glacial and ice sheet melt as well as sea level rise, including greenhouse gas concentrations, global temperatures, and subsurface ocean temperatures.

Using the Community Climate System Model version 3 from the National Center for Atmospheric Research, the research team ran simulations for more than 25,000 model years using conditions and climate reconstructions surmised from data collected around the globe.

That includes greenhouse gases measured in deep ice cores, sea level indicators in corals, and cave features called speleothems. The simulations also included the position of the planet relative to the sun, ice sheet data and changes in heat transport associated with changes to AMOC.

The study found that AMOC was reduced in a single step at the transition of the last interglacial for roughly 7,000 years. During the transition into the current interglacial period, the Holocene, AMOC reduction lasted only about two-thirds as long and occurred in two steps.

During both transitions, however, AMOC reduction caused subsurface warming throughout the Atlantic Basin, which agrees with observed data. The reduction resulted in more sea ice in the North Atlantic Ocean and the reduction of ocean convection. Both of these reduce heat loss from the surface ocean, warming the subsurface, similar to the way in which winter snow helps insulate the ground below.

“Though we have known for a long time that sea levels rose during this past warm period, this study helps us to identify why and how that happened,” says Andrea Dutton, study co-author, professor of geoscience at UW–Madison, and a current Fulbright scholar at the Antarctic Research Centre in New Zealand. “In particular, this new work points to the importance of the warming of the ocean in destabilizing marine-based ice sheets.”

In the U.S., four out of ten people live in populous coastal areas, making them vulnerable to the effects of rising seas. Seventy percent of the world’s largest cities are located near a coast.

Globally, by 2010, seas had already risen about 10 inches above their average levels in pre-industrial times. According to the National Oceanic and Atmospheric Administration, in 2014 they were rising at an increasing rate of roughly one-eighth of an inch each year.

Also by 2014, global temperatures had increased by 1 degree Celsius (1.8 deg Fahrenheit) relative to pre-industrial conditions, representing the same amount of warming that led to sea level rise during the last interglacial period.

“This is really scary because on paper at least, it shows that six to nine meters of sea level rise can occur with the same amount of global warming happening right now,” says He.

“The Antarctic Ice Sheet is very susceptible to warming from the ocean so if we want to reduce the uncertainty of sea level rise from the Antarctic we need to monitor where subsurface warming will occur, with more ice sheet modeling development,” He says. “Sea level rise is the number one threat of global warming.”