Study: Earth's polar ice sheets vulnerable to even moderate global warming

December 16, 2009

A new analysis of the geological record of the Earth's sea level, carried out by scientists at Princeton and Harvard universities and published in the Dec. 16 issue of Nature, employs a novel statistical approach that reveals the planet's polar ice sheets are vulnerable to large-scale melting even under moderate global warming scenarios. Such melting would lead to a large and relatively rapid rise in global sea level.

According to the analysis, an additional 2 degrees of global warming could commit the planet to 6 to 9 meters (20 to 30 feet) of long-term sea level rise. This rise would inundate low-lying coastal areas where hundreds of millions of people now reside. It would permanently submerge New Orleans and other parts of southern Louisiana, much of southern Florida and other parts of the U.S. East Coast, much of Bangladesh, and most of the Netherlands, unless unprecedented and expensive coastal protection were undertaken. And while the researchers' findings indicate that such a rise would likely take centuries to complete, if emissions of greenhouse gases are not abated, the planet could be committed during this century to a level of warming sufficient to trigger this outcome.

The study, "Probabilistic Assessment of Sea Level During the Last Interglacial Stage," was written by Robert Kopp, who conducted the work as a postdoctoral researcher in Princeton's Department of Geosciences and Woodrow Wilson School of Public and International Affairs; Frederik Simons, an assistant professor of geosciences at Princeton; Jerry Mitrovica, a professor of geophysics at Harvard; Adam Maloof, an assistant professor of geosciences at Princeton; and Michael Oppenheimer, a professor of geosciences and international affairs in Princeton's Woodrow Wilson School.

As part of the study, the researchers compiled an extensive database of geological sea level indicators for a period known as the last interglacial stage about 125,000 years ago. Polar temperatures during this stage were likely 3 to 5 degrees Celsius (5 to 9 degrees Fahrenheit) warmer than today, as is expected to occur in the future if temperatures reach about 2 to 3 degrees Celsius (about 4 to 6 degrees Fahrenheit) above pre-industrial levels.

"The last interglacial stage provides a historical analog for futures with a fairly moderate amount of warming; the high sea levels during the stage suggest that significant chunks of major ice sheets could disappear over a period of centuries in such futures," Kopp said. "Yet if the global economy continues to depend heavily on fossil fuels, we're on track to have significantly more warming by the end of century than occurred during the last interglacial. I find this somewhat worrisome."

Oppenheimer added, "Despite the uncertainties inherent in such a study, these findings should send a strong message to the governments negotiating in Copenhagen that the time to avoid disastrous outcomes may run out sooner than expected."

Previous geological studies of sea level benchmarks such as coral reefs and beaches had shown that, at many localities, local sea levels during the last interglacial stage were higher than today. But local sea levels differ from those in this earlier stage; one major contributing factor is that the changing masses of the ice sheets alter the planet's gravitational field and deform the solid Earth. As a consequence, inferring global sea level from local geological sea level markers requires a geographically broad data set, a model of the physics of sea level, and a means to integrate the two. The study's authors provide all three, integrating the data and the physics with a statistical approach that allows them to assess the probability distribution of past global sea level and its rate of change.

The researchers determined through their analysis that there is a 95 percent probability that, during the last interglacial stage, global sea level peaked more than 6.6 meters (22 feet) above its present level. They further found that it is unlikely (with a 33 percent probability) that global sea level during this period exceeded 9.4 meters (31 feet).

Sea levels during the last interglacial stage are of interest to scientists and important to policymakers for several reasons. Most notably, the last interglacial stage is relatively recent by geological standards, making it feasible for climate scientists to develop a credible sea level record for the period, and is the most recent time period when average global temperatures and polar temperatures were somewhat higher than today. Because it was slightly warmer, the period can help scientists understand the stability of polar ice sheets and the future rate of sea level rise under low to moderate global warming scenarios.

The findings indicate that sea level during the last interglacial stage rose for centuries at least two to three times faster than the recent rate, and that both the Greenland and West Antarctic ice sheet likely shrank significantly and made important contributions to sea level rise. However, the relative timing of temperature change and sea level change during the last interglacial stage is fairly uncertain, so it is not possible to infer from the analysis how long an exposure to peak temperatures during this stage was needed to commit the planet to peak sea levels.
-end-


Princeton University

Related Global Warming Articles from Brightsurf:

The ocean has become more stratified with global warming
A new study found that the global ocean has become more layered and resistant to vertical mixing as warming from the surface creates increasing stratification.

Containing methane and its contribution to global warming
Methane is a gas that deserves more attention in the climate debate as it contributes to almost half of human-made global warming in the short-term.

Global warming and extinction risk
How can fossils predict the consequences of climate change? A German research team from Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), the Museum of Natural History Berlin and the Alfred Wegener Institute compared data from fossil and marine organisms living today to predict which groups of animals are most at risk from climate change.

Intensified global monsoon extreme rainfall signals global warming -- A study
A new study reveals significant associations between global warming and the observed intensification of extreme rainfall over the global monsoon region and its several subregions, including the southern part of South Africa, India, North America and the eastern part of the South America.

Global warming's impact on undernourishment
Global warming may increase undernutrition through the effects of heat exposure on people, according to a new study published this week in PLOS Medicine by Yuming Guo of Monash University, Australia, and colleagues.

Global warming will accelerate water cycle over global land monsoon regions
A new study provides a broader understanding on the redistribution of freshwater resources across the globe induced by future changes in the monsoon system.

Comparison of global climatologies confirms warming of the global ocean
A report describes the main features of the recently published World Ocean Experiment-Argo Global Hydrographic Climatology.

Six feet under, a new approach to global warming
A Washington State University researcher has found that one-fourth of the carbon held by soil is bound to minerals as far as six feet below the surface.

Can we limit global warming to 1.5 °C?
Efforts to combat climate change tend to focus on supply-side changes, such as shifting to renewable or cleaner energy.

Global warming: Worrying lessons from the past
56 million years ago, the Earth experienced an exceptional episode of global warming.

Read More: Global Warming News and Global Warming Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.