During the last interglacial—a warm period between ice ages 125,000 years ago—global average temperatures similar to today led to a sea level rise of 6-9 metres, caused by melting ice in Greenland and Antarctica, according to new research published in Science Journal.
This means “the agreement to keep global average temperature (rise) below 2°C… carries substantial risk of unmanageable sea level rise,” the researchers warned.
The new study was released as a large group of scientists gathered in Paris this week to warn politicians that the current level of commitment and action will lead the planet towards a 3 to 5 degrees Celsius rise.
While there is ongoing debate over safe levels of warming, countries round the world have pledged to try and limit the average global temperature rise to 2 degrees Celsius above pre industrial figures. Many scientists have already warned this is not achievable given the current rates of carbon dioxide emissions.
The researchers from the international project Past Global Changes said they analysed sea levels during several warm periods in the Earth’s recent history when global average temperatures were similar to or slightly warmer than today—about 1 degree above pre-industrial level.
“While the global average temperature rises of 1 to 3 degrees seem small, they were, like today, linked with magnified temperature increases in the polar regions which sustained over many thousands of years,” said Andrea Dutton, lead author and assistant professor at the University of Florida.
The researchers say it is not yet possible to accurately estimate the rate of sea-level rise during these periods and that more research is needed.
Their findings corroborate with an earlier 2008 study by scientists at Princeton which showed global sea levels could rise by up to 9 metres in the next few hundred years.
According to the fifth assessment report of the Intergovernmental Panel on Climate Change (IPCC)—the UN’s top climate science body—sea level rise is picking up pace. Between 1993 and 2010 the global sea level rose by 3.2 mm per year—almost double the longer period average. The report claims that current levels of emissions will lead to a temperature rise of 3.2 to 5.4 degrees above pre industrial levels.
Such a rise would be catastrophic for coastal areas, where the majority of people live. The IPCC has warned that coastal areas in large deltas are especially vulnerable. Mumbai, Kolkata, Karachi, Dhaka and Shanghai are among cities considered most at risk.