Scientists warn that even with an ambitious goal of limiting global warming to 1.5 degrees Celsius, the world may see sea level rise by several meters or more meters or more.

Nearly 200 countries have pledged to try to keep the planet warming at 1.5C, but researchers warn that this should not be considered "safe" for coastal populations.

They came to the conclusion after reviewing the latest research on how ice sheets change and how they changed in the past.

But scientists stress that some degree of warmth that can be avoided will still greatly limit the risk.

Compared to the late 1800s, by the end of this century, the current trajectory of the world allowed the planet to burn a large amount of planet-heated fossil fuels in the course of nearly 3C. This is based on current government policies to reduce carbon emissions in fossil fuels and other pollution activities.

However, since temperature changes can take hundreds of years to have full impact on such a large ice layer, Greenland and Antarctic will continue to melt even if it is maintained at 1.5°C.

"Our key message is that limiting warming to 1.5C would be a major achievement - it should definitely be our goal - but it will definitely not slow or stop sea level rise and melt the ice sheet."

The 2015 Paris Climate Agreement allowed countries around the world to agree to keep global temperatures “well below” 2C, ideally 1.5C.

Glacierologists have been warning for years that this is often too simple to mean that the 1.5C is "safe".

The authors of the new paper, published in the journal Communication Earth and the Environment, bring together three main evidence to highlight the case.

First, during the same warm periods before (e.g. 125,000 years ago), the distant past records of the Earth show that sea levels are several meters higher than they are now.

The last time in the atmosphere was as much carbon dioxide as today's - about 3 million years ago - sea level was about 10-20m high.

Second, current observations have shown an increase in melting rate, although it changes every year.

"Things have happened quite drama in Antarctica and Greenland," said Professor Jonathan Bamber, director of the Bristol Center for Glacierology.

Eastern Antarctica looks at least more stable.

Professor Stokes added: "We started to see some of these worst-case scenarios almost played a role in front of us."

Finally, scientists use computer models to simulate how the ice sheets cope with future climates. The pictures they draw are not good.

"In fact, few models show that sea level rise is slowing down (if the warming stabilizes at 1.5C), and they certainly don't show a stop to sea level rise," Professor Stokes said.

The main problem is that melting may further accelerate the “cutting point” due to human-induced warming – although it is unclear how these mechanisms work and where these thresholds are located.

"The advantage of this study is that they use multiple evidence that our climate is similar to the state of melting several meters of ice in the past," said Andy Shepherd, a glacologist at Northumbria University.

"This will have a devastating impact on coastal communities," he added.

An estimated 230 million people live within one meter of the current climax line.

Defining the “safe” warming limit is inherently challenging because some populations are more vulnerable than others.

But if by the end of the century (mainly due to melting ice and warming oceans), even if sea levels rise to a year or more, this could expand the response capacity of wealthy countries.

"If this level is reached, it will become extremely challenging for any form of adaptation strategy, and you will see large-scale migrations at scales (in modern civilizations) that we have never seen before."

However, this bleak picture is not the reason to stop trying, they said.

"The faster you warm, you'll see more ice loss (and higher sea level rises faster and faster," Professor Stokes said.

“A small portion is really important for the ice sheet.”

Other reports by Phil Leake