Global warming is causing the ice caps to melt and subsequently sea levels to rise.
While this poses a risk to low lying coastal cities in itself, there is an added danger.
These coastal cities will ultimately be more vulnerable to tsunamis as a result of smaller earthquakes in the future.
Researchers focused on the territory of Macau, located on China’s southern coast.
The region is currently situated in a major earthquake zone, but is not at any real risk from a tsunami – it would take a magnitude 8.8 to cause widespread tsunami flooding in Macau.
However, a half metre rise in sea levels – which is predicted by 2060 – will almost double the risk of tsunamis.
A three-foot sea level rise, which according to current models will come by 2100, would increase the risk up to 4.7 times.
The source of the earthquake danger is the Manila Trench, a massive crack in the floor of the South China Sea formed by the collision of two tectonic plates.
Lead researcher Dr Robert Weiss, from Virginia Polytechnic Institute and State University (Virginia Tech) in the US, said: “Our research shows that sea-level rise can significantly increase the tsunami hazard, which means that smaller tsunamis in the future can have the same adverse impacts as big tsunamis would today.
“The South China Sea is an excellent starting point for such a study because it is an ocean with rapid sea-level rise and also the location of many mega cities with significant worldwide consequences if impacted.”
The researchers added that the newly discovered risk is vital for policymakers to factor in in future situations when deciding how to protect coastlines from rising sea levels.
The team, whose findings have been published in the journal Science Advances, said: “Although the vulnerability of coastal communities to rising seas is well known, the capacity for a single tsunami event to devastate coastal areas is rarely considered in coastal planning.”