(CNN) Global sea levels could rise more than two meters (6.6 feet) by the end of this century if emissions continue unchecked, swamping major cities such as New York and Shanghai and displacing up to 187 million people, a new study warns.

The study, which was released Monday, says sea levels may rise much faster than previously estimated due to the accelerating melting of ice sheets in both Greenland and Antarctica.

The international researchers predict that in the worst case scenario under which global temperatures increase by 5 degrees Celsius (9 degrees Fahrenheit) by 2100, sea levels could rise by more than two meters (6.6 feet) in the same period -- double the upper limit outlined by the UN climate science panel's last major report.

Such a situation would be "catastrophic," the authors of the study warn.

"It really is pretty grim," lead author Jonathan Bamber, a Professor of Physical Geography at the University of Bristol told CNN. "Two meters is not a good scenario."

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