Digging for historical climactic clues buried deep in ice, scientists are trying to determine how much time coastal cities have before rising sea levels render them uninhabitable.
Experts previously thought that Greenland’s ice sheet was the major source of water causing increased sea levels in the Earth’s warmer past. However, information locked in cores of ice drilled from Greenland’s ice sheet indicates that this is not true, according to James White, director of the University of Colorado’s Institute of Arctic and Alpine Research. These preliminary results have important implications for predicting the timing and severity of future sea level rise on those living in at-risk areas.
“Miami doesn’t have a future beyond the end of this century” White warns. By that time, sea level is expected to rise by at least one meter sea, which would put Miami underwater. “The big question is: how fast are we going to get there?”
To answer this question, White and a team of international researchers involved in the North Greenland Eemian Ice Drilling project (NEEM) have been working over the past three years to obtain ice cores going 1.5 miles deep into the ice sheet, right down to bedrock — and probing over 150,000 years of climate history. Using chemical clues in the ice along with radar imaging of the ice sheet and data from previous drilling projects, researchers can determine which layers in the ice were on the surface at different points in history. They can then “reverse time,” as White puts it, and build a picture of what the ice sheet looked like in the past.
White and his NEEM colleagues are focusing on the most recent “interglacial” period, known as the Eemian period, which occurred about 100,000 years ago. Interglacial periods represent eras of warmer global temperatures that occur sandwiched between times when the planet was covered with glaciers.
During the Eemian, the planet was actually 3 to 5 degrees Fahrenheit warmer on average than it is today, and the sea level was 5-8 meters higher.
This is important because due to human-induced warming from greenhouse gases, the future for the planet’s climate will approach the temperatures last seen during the Eemain period. The behavior of Greenland’s ice sheet during past warm periods holds information that helps climate modelers predict their future behavior.
“It is critical that scientists understand how the ice sheets responded in the past, so they can begin to predict the future effects of climate change” said White.
Before the NEEM research, experts had theorized that during the Eemian period the Greenland ice sheet melted out to half of its current size, causing 50 to 70 percent of the sea level rise that occurred. However, the results from the NEEM cores do not support this theory, as only a 25 percent reduction of the ice sheet was observed, according to White.
This means that researchers need to start looking elsewhere for unstable ice sheets that could have caused the sea levels to be 5 to 8 meters higher – most likely Antarctica. This could be catastrophic for coastal cities like Miami. That’s because, unlike Greenland’s ice sheet, the bottom of the West Antarctic Ice Sheet, or WAIS, lies below sea level, indicating that the ice sheet could be prone to sudden collapse with a concurrent rapid sea level rise. Perhaps too rapid for heavily populated coastal areas like Miami — and entire countries like Bangladesh — to adapt.
“A lot of our attention has been focused on Greenland and now the time has come to focus our attention on Antarctica,” White said. “We need to know where melting will come from and how fast it is going to melt today to answer questions like how long Miami has and after Miami – what is next?”