Sea levels could rise by 6 meters (20 feet) in the long rung even if a United Nations goal of limiting global warming to 2 degrees Celsius (3.6 Fahrenheit) above pre-industrial times is reached, according to researchers at Past Global Changes project.
Three times in the recent geological past sea levels were at least 6 meters higher than current levels when global average temperatures were similar to today, according to the study published in the journal Science.
Nations have agreed to try to limit global average temperature to no more than 2°C above pre-industrial levels, while warming is on course to reach 4°C degrees by the end of this century if emissions continue on the current trajectory, according to the Intergovernmental Panel on Climate Change Fifth Assessment Report 2013.
On top of this, the rise in global average temperature might be inaccurate, as NASA recently discovered that in recent years extra heat from greenhouse gases has been trapped in the waters of the Pacific and Indian oceans, accounting for the slowdown in the global surface temperature trend observed during the past decade.
While the global average temperature rises of 1 to 3°C seem small, they were, like today, linked with magnified temperature increases in the polar regions which sustained over many thousands of years.
”During recent interglacial periods, global average temperatures similar to today, but slightly higher polar temperatures, resulted in more than 6 metres of global average sea-level rise,” lead author, Assistant Professor Andrea Dutton, University of Florida, said.
”The poles are on course to experience similar temperatures in the coming decades.”
The Arctic is currently warming faster than the global average. And while world leaders have agreed to keep global average temperature below 2°C, even this level sustained over a long period of time carries substantial risk of unmanageable sea-level rise, not least because carbon dioxide remains in the atmosphere for over a thousand years, according to the study.
A key question for societies is, how fast did sea levels rise? The researchers say it is not presently possible to accurately ascertain the rate of sea-level rise during these previous warm periods and that more research is needed in this direction.
The researchers, members of PALSEA2 (PALeo constraints on SEA level rise 2), a group that investigates past sea-level rise and is hosted by the Past Global Changes (PAGES) project, used computer models and evidence from around the globe to arrive at their conclusions.
”This study confirms that our present climate is warming to a level associated with significant polar ice-sheet loss in the past. Studies such as these that improve our understanding of magnitudes of global sea-level rise due to polar ice-sheet loss, are critical for society, perhaps the most societally relevant information the paleo record can provide,” said co-author Associate Professor Anders Carlson of Oregon State University and leader of the PALSEA2 Working Group.