New studies released on Monday show that a large portion of the West Antarctic Ice Sheet may have begun a slow but "unstoppable" collapse, with the demise of these glaciers taking place sometime during the next few centuries to as many as 1,000 years from now.

The findings do not significantly alter short-term sea level rise projections, but they mean that we may need to prepare for larger amounts of long-term sea level rise than previously thought.

The global average sea level has already risen by about eight inches since 1901, with up to another two and a half feet of sea level rise possible by 2100, according to the most recent projections from the U.N. Intergovernmental Panel on Climate Change.

The new research, published in the journals Science and Geophysical Research Letters, shows that global averaged sea level could increase by 4 feet just from glacial melting in a portion of West Antarctica during the next few centuries. The rate of this sea level rise is important, and a big unknown at this point, since a 4-foot sea level rise over the course of 200 years will be harder for coastal cities to adapt to compared to if the same amount of sea level rise were to play out during, say, 900 years.

Four feet of sea level rise is sufficient to escalate flooding risks for many major cities in the U.S.

Over the long-term, melting of the West Antarctic Ice Sheet could yield as much as 10 to 14 feet of global average sea level rise, with local sea level rise varying considerably depending on land elevation trends, ocean currents and other factors.

With the caveat that this much global average sea level rise is almost certainly not going to occur during the next several decades, here is what New York City would look like with a 10-foot increase in the local sea level, with blue areas showing areas that would be inundated (many more areas would be flooded during a storm event). The map below shows that much of Lower Manhattan would be under water, including the base of the new Freedom Tower, along with pricey real estate in Brooklyn and the East Village. These projections are screenshots from Climate Central's Surging Seas sea level rise tool, which is based on peer-reviewed research.

Projection for areas flooded in New York City if water levels reached 10 feet above high tide. Areas in dark blue are inundated areas, areas in white are on dry ground. Image: Climate Central

And here is how New York City's busiest airport, John F. Kennedy International, would fare under a 10-foot sea level rise scenario:



Projected flooding at Kennedy International Airport in New York if water levels were to reach 10 feet above the current high tide line. The entire airport would flood in such a scenario. Image: Climate Central

Florida is the most at-risk state from a sea level rise perspective, with 2,120 square miles of land sitting at less than three feet above the high tide line. This includes $145 billion in property value, according to Climate Central research. That figure jumps to $544 billion in property value that would be at risk if the ocean were to reach six feet above the high tide line.

A 10-foot increase in sea level would essentially render all of South Florida, from Naples on the west coast to Ft. Lauderdale in the east, under water. This includes almost all of Miami.

Virtually all of South Florida would be inundated under a 10-foot sea level rise scenario. Image: Climate Central

Then again, even just four feet of sea level rise would put Miami Beach under water.

Projection for how Miami Beach would fare if water levels rose to four feet above the high tide line. Much of Miami Beach would be flooded. Image: Climate Central

The impacts of sea level rise, in the form of higher storm surges and increasingly common flooding at times of astronomical high tides, are already causing damage in the U.S. and worldwide. For example, when Hurricane Sandy struck New York City in 2012, it hit an area where the sea level was about a foot higher than it had been a century before. This may have resulted in as many as an additional 40,000 people affected by flooding than otherwise would have been.

While the melting of Antarctica and the associated long-term sea level rise will take many centuries to play out, near-term sea level rise from what is currently a relatively slow melt of land-based ice sheets will cost more money and lives with each passing year and each coastal storm.

Brooke C. Medley, a postdoctoral fellow with NASA who contributed to one of the new papers on Antarctic ice loss, said the findings demonstrate that the planet's large ice sheets, which were once thought to be stable, are responding to global warming and other influences at a rapid rate.

"This work along with other observations and modeling efforts over the past decade or two have revealed that these large ice sheets are responding on timescales relevant to mankind," she said in an email to Mashable.

Medley says that while the "collapse" of West Antarctic glaciers, such as the Thwaites Glacier, may take centuries to play out, these glaciers will still be a key source of shorter-term sea level rise as well.