A study has suggested global sea levels could rise by an astonishing amount if greenhouse gas emissions remain high – coupled with some bad luck.

Published in the journal Annual Review of Environment and Resources, researchers in the US and Singapore said global average sea levels could rise by almost 2.5 meters (8 feet) by 2100 and 15 meters (50 feet) by 2300.

This would cause catastrophic issues for the global population; about 11 percent of the 7.6 billion people in the world currently live less than 10 meters (33 feet) above sea level. 

"There's much that's known about past and future sea-level change, and much that is uncertain. But uncertainty isn't a reason to ignore the challenge," study co-author Dr Robert Kopp, from Rutgers University-New Brunswick, said in a statement. "Carefully characterizing what's known and what's uncertain is crucial to managing the risks sea-level rise poses to coasts around the world."

The study comes on the back of a landmark UN climate report, which said the world was not doing enough to keep global warming below a rise of 2°C since pre-Industrial times. That report urged the time to act was now, and we needed to aim for a rise of no more than 1.5°C.

The global average sea-level has risen by 0.06 meters (0.2 feet) since 2000. A rise of up to 0.8 meters (2.8 feet) is expected by 2100 under moderate emissions, 1.6 meters (5.4 feet) by 2150, and 4.3 meters (14 feet) by 2300.

That upper level of 50 feet by 2300 is the top extreme, if emissions remain unchecked, with a one-in-20 chance of occurring. Dr Kopp told IFLScience that was also dependent on some bad luck, if "physics that are currently deeply uncertain break against us," he said.

"There are two main types of relevant uncertainty – those that relate to human behavior (how high emissions are) and those that relate to physics (whether ice sheets are relative stable or unstable)," he said. "The former is in human control; the latter is just down to luck."

Other research this month predicted that between 1.5 and 5.4 percent of the world’s population could be exposed to flooding by 2300, depending on what action we take.

“These results indicate the importance and benefits of climate change mitigation on fragile and vulnerable environments, such as small islands or low-lying highly populated deltas," Dr Ivan Haigh, from the University of Southampton in the UK, said in a statement on those findings.

While the numbers vary somewhat, the overall message is clear. Continuing on our current path of warming the planet will have very dire consequences for the world, particularly in the long-term. And in a worst-case scenario, our future descendants may just be left wondering why the hell people in our time didn’t do anything to stop it.