Climate change has been steadily shifting the planetary environment in myriad ways, from receding glaciers and melting sea ice to longer and more intense heat waves, droughts and storms. The changing environment has pushed many plant and animal species out of their normal habitats. And one dramatic effect is going to force humans to relocate: the rise in sea level.

The rising seas are caused by the additional water coming from melting land ice, as well as the expansion of seawater, which happens when it warms. Since reliable record keeping began in 1880, the global sea level has risen by approximately 8 inches. Scientists project that by 2100, the ocean may rise an additional 1 to 4 feet. And it won't stop there, says NASA, "because the oceans take a very long time to respond to warmer conditions at the Earth’s surface."

Making matters worse, storm surges from an increase in extreme weather—again, a product of manmade climate change—will likely increase flooding in regions already impacted by sea level rise. In many areas, these surges could push sea levels to at least 4 feet above high tide by 2030. By 2050, threatened areas hit by serious storms could experience surges up to 5 feet higher than high tide.

And that’s not all. Almost unbelievably, the Greenland and Arctic ice sheets are so massive that they actually exert a gravitational pull on the ocean, causing even higher sea levels for nearby coastlines to deal with.

According to Climate Central, an independent environment nonprofit, "Carbon emissions causing 4°C of warming—what business-as-usual points toward today—could lock in enough sea level rise to submerge land currently home to 470 to 760 million people, with unstoppable rise unfolding over centuries."

That’s because even if humanity were to stop emitting carbon altogether right now, the carbon we’ve already put into the atmosphere will continue to heat up the planet for hundreds of years to come.

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This NASA chart tracks the change in sea level since 1993 as observed by satellites. The rate of change has been 3.4mm per year. (image: NASA)

For some island nations, the rising sea has already claimed several landmass victims. The Solomon Islands has experienced annual sea levels rise as much as 10mm over the past two decades, according to an Australian study published in May in the online journal Environmental Research Letters. Earlier this year, the ocean swallowed up five of the archipelago's islands—a breathtaking event that is believed to be the first scientific confirmation of the climate change impact on Pacific coastlines. The scientists say their study "confirms the numerous anecdotal accounts from across the Pacific of the dramatic impacts of climate change on coastlines and people."

The islands, which were uninhabited, ranged in area from 2.5 to 12.4 acres. However, large tracts of land across six different inhabitated islands had large swaths of land washed into the sea. On two of those, entire villages were destroyed and people forced to relocate. "The sea has started to come inland, it forced us to move up to the hilltop and rebuild our village there away from the sea," said Sirilo Sutaroti, the 94-year-old leader of the Paurata tribe on Nararo Island.

But tiny Pacific islands aren't the only places that will be severely impacted by rising seas. Here in the United States, coastal areas have already felt the impact and many cities are making preparations for the future. From New York to Sacramento, Jacksonville to Virginia Beach and even remote Alaskan fishing villages, millions of Americans in more than 400 municipalities live within just four feet of the current high tide line. According to a 2015 study conducted by American and German researchers, it's already too late for many of those cities—including Miami and New Orleans—which are on track to be overcome by the rising sea.

A 2012 study by the U.S. Geological Survey found that portions of the U.S. Atlantic coast are experiencing rates of sea-level rise that are three to four times faster than global rates over the past quarter century. "Since about 1990, sea-level rise in the 600-mile stretch of coastal zone from Cape Hatteras, N.C. to north of Boston, Mass.—coined a 'hotspot' by scientists—has increased 2 – 3.7 millimeters per year; the global increase over the same period was 0.6 – 1.0 millimeter per year," USGS said.

"New York has experienced at least a foot of sea-level rise since 1900, mostly due to expansion of warming ocean water," according to the New York Department of Environmental Conservation, noting that by 2100, current projections have the city's sea level as much as 50 inches higher than it is today.

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This NASA chart, derived from coastal tide gauge data, shows how much sea level changed from about 1870 to 2000. (image: NASA)

In 2007, New York's lawmakers created a statewide Sea Level Rise Task Force to review the projections and prepare for the future. In its 2011 final report, the task force concluded that, "while the extent of the impacts to coastal communities from a rising sea are not fully known, even the most conservative projections make clear that there will be dramatic changes in this century." They warned that every single New York tidal coastal community would be impacted by sea-level rise. That includes, of course, New York City, America's most populated urban center.

The task force made several recommendations, including providing financial support for adaptation-planning, post-storm recovery and redevelopment.

"Climate change is one of the biggest challenges facing our city, our country and our planet," said New York Mayor Bill de Blasio in April, as he announced the Raised Shorelines project to help low-lying neighborhoods mitigate impacts of sea-level rise, part of the city's $20 billion climate resiliency program. "For a coastal city like ours, rising sea levels mean rising risk for our neighborhoods, infrastructure and economy," de Blasio said.

But mitigation can only go so far. Under the worst-case scenario, New York could be unlivable by the year 2085.

While scientists are sure that the seas will continue to rise, what’s unclear is how fast they will rise, and which regions will be the most impacted. "This is the burning question," said Andrea Dutton, an assistant professor of geology at University of Florida. "How quickly will the sea levels rise, and by how much?"

This animated timeline maps, year by year, how the total number of locked-in cities could climb to more than 1,500, if pollution continues unchecked through the end of the century. (infographic: Climate Central)

While Dutton's university is safely inland (for now), Florida is viewed by researchers as ground-zero for disastrous sea-level rise. The Miami chapter of the Southeastern Florida Compact—a local climate-change coalition whose members include city officials, scientists and concerned citizens—is only planning in five-year cycles. "Nobody knows what things are going to look like in 50 to 100 years," said Nicole Hefty, chief of the Office of Sustainability at Miami-Dade County. "We can speak for smaller years and adapt in that way."

"Florida is in the crosshairs of climate change," writes Ben Strauss, a vice president at Climate Central, which spent two years analyzing the specific threat to the Sunshine State. "Rising seas, a population crowded along the coast, porous bedrock, and the relatively common occurrence of tropical storms put more real estate and people at risk from storm surges aggravated by sea-level rise in Florida, than any other state by far."

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Florida – 1 meter sea level rise. (image: Maitri/Flickr CC)

Strauss points out that in Florida, around 2.4 million people live within just 4 feet of the local high tide line. That’s almost half the national risk right there. In Miami-Dade and Broward counties alone, there are "more people below 4 feet than any state, except Florida itself and Louisiana," he adds. After the Sunshine State, the next three states that will most likely be overcome by rising ocean water are California, Louisiana and New York.

Andrew Freeman, the science editor at Mashable, writes that in New York City, "the contrast between the high emissions scenario and low emissions scenario would mean the difference between submerging all of newly trendy Red Hook and Cobble Hill neighborhoods in Brooklyn, New York, as well as the new Brooklyn Bridge Park and a swath of prized real estate in southwest Manhattan, versus keeping those areas dry."

Taking action on climate change now—particularly to avoid the "business-as-usual" 4°C global surface temperature increase—could mean the difference for countless communities across the world. That action is in the works: on November 4, the Paris climate agreement went into effect. The deal seeks to limit global warming to "well below" 2°C above pre-industrial temperatures. But the accord isn’t bound by law; there are no penalties imposed on nations that fail to meet their carbon reduction targets.

The fact that the agreement is non-binding has been a source of ridicule among many environmentalists. But that doesn't render it meaningless, argues Michael Burger, executive director of the Sabin Center for Climate Change Law at Columbia Law School. "International agreements operate under good faith," he said. "Whether a country is an upstanding member of the international community is what's at stake."

In the coming decades, humanity's energy choices are critical—particularly in China and the U.S., which together account for nearly 40 percent of worldwide emissions. The choices we make today will determine whether or not future generations will be living in a low-emissions scenario or the current business-as-usual trajectory.

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The infographic above was produced by Eco2greetings.com.