Last December, the world’s politicians finally acknowledged what almost every climatologist has been saying for ages: The world is warming, and we are mostly responsible. A new study published in the journal Nature reveals just how catastrophic our manipulation of the world’s climate may be. By 2500, the continued melting of the Antarctic land ice will cause a whopping 15 meters (about 49 feet) in global sea level rise.

“This could spell disaster for many low-lying cities,” said Prof. Robert DeConto, a climatologist from the University of Massachusetts Amherst and co-author of the study, in a statement. “For example, Boston could see more than 1.5 meters [about five feet] of sea-level rise in the next 100 years.”

The study of the effects of climate change is notoriously complex and incredibly difficult, simply because there are so many factors and variables to consider. Calculating the effect of melting land ice on sea level rise is no exception to this, which explains why there is now a huge range of studies giving very different estimations in this regard.

In 2013, the Intergovernmental Panel on Climate Change (IPCC) predicted a rise of 98 centimeters (3.2 feet) by the end of the century if the current rate of emissions continues unabated. This is considered to be a minimum estimate, and several other studies have reached more severe conclusions: One has suggested that the rise is likely to be around 1.31 meters (4.29 feet).

David Pollard, a paleoclimatologist and co-author of this study, describes his research on Antarctic ice-sheet melting. Pennsylvania State University

One far more conservative estimate concludes that there will just be a 10 centimeter (3.9 inch) increase by 2100. This study is certainly one of the most high-end calculations to date, as it predicts that by 2100, there will be 1.14 meters (3.74 feet) of sea level rise from just Antarctic melting. This value will be around 1.83 metres (six feet) when other ice masses around the world are taken into account, almost double the IPCC estimate.

So why the differences? As it turns out, ice is complicated, and doesn’t all simply fall into the sea and cause it to rise. Ice shelves, for example, are already floating on the sea, so their collapse doesn’t contribute to sea level rise. They do, however, act as dams for glaciers behind them, and their disintegration means that these glaciers, which do contribute to sea level rise, will tumble into the sea – but scientists cannot be sure at what speed they will do so.

The movement of the land-based ice sheets is also quite tricky to predict. Previous studies have focused on the action of increasingly warmer sea waters lapping up against them, wherein the ice “grounding” them to the rock beneath is eroded away. This new study takes into account the effect of surface water dripping down from above and accelerating the destruction of their bases.

This cutting-edge model includes the effect of undercutting ice sheets (a-c) and the collapse of ice cliffs by percolating surface water (d-f). DeConto & Pollard/Nature

Combined with the crumbling of the damming ice shelves and atmospheric warming, as well as sea surface warming, the authors of this study are confident that the next decade will produce a sudden uptick in ice deposition into the sea. They tested their cutting edge model by attempting to replicate past sea level rises, which they did correctly.

So it looks fairly certain that New York City will be almost entirely submerged by 2500 – unless, of course, we actually do something about it.