There's mounting evidence that the human race is making long-term changes to the Earth's climate — CO2 levels recently reached a peak not seen in millions of years, NASA found 2012 to be the ninth-warmest year on record, and a study recently showed that it was all but certain Miami would eventually be underwater thanks to rising sea levels. However, according to a new study published by PNAS, Miami is hardly the only city facing an underwater future. According to Dr. Benjamin Strauss, a researcher who specializes in climate impacts, the greenhouse gases we've already pumped into the atmosphere have "locked-in" an eventual sea level rise of over 4 feet — enough to submerge more than half of the current population in 316 coastal US cities — some 3.6 million people.

The future looks wet

Strauss' findings rely on data from a climate change study published earlier this month by PNAS that showed for every degree Fahrenheit of global warming due to carbon pollution, the sea level would eventually rise about 4.2 feet. From there, Strauss combined that with current rates of carbon emissions, estimates for global temperature sensitivity due to those emissions, and data from Climate Change's Surging Seas project (which Strauss calls a "national assessment and mapping of coastal vulnerability in the U.S. based primarily on elevation and census data"). Based on those sources, Strauss put together not only the projection that affects the 316 cities and 3.6 million people but also projections going years into the future, as far as the year 2100 — you can see his findings in the interactive map below.

The map lets you see specifically what cities in each state are threatened in each decade going from now through the end of the century, with a variety of variables that can change the projection significantly. You can decide whether to use current polution levels or a "deep cuts" scenario in which we significantly curtail our creation of greenhouse gases. On the right, you can decide the "affected population" threshold — it dictates how much of a city's population needs to be affected by the rising sea levels to include it in this list.

There's a lot of variability in this model

By the end of this decade, and using a 50 percent threshold for defining an impacted city, Strauss predicts that both Florida and Louisiana could be significantly affected by the estimated five-foot sea level increase — Florida alone would have 150 threatened towns with a population of 2.7 million, while Louisiana would add another 1.2 million people and 114 towns to the list. Hundreds of thousands more would be affected across California, New Jersey, North Carolina, and other states.

Taking his projection all the way out ot the end of the century, Strauss found a scenario that rising sea levels of 23 feet would submerge over 1,400 cities and towns and affect over 18 million people — but if we were able to curtain our greenhouse gas production under his "deep cut" scenario, the sea level would rise only 7.5 feet, while the number of towns affected would drop to 555.

It's quite the dramatic study, but it's worth noting that these are simply projections rather than realities. Strauss notes that his model does not take into account any engineering feats that might keep these cities protected from rising sea levels; it's based only on a city's elevation. And while there's any number of things that could change in the coming years that could easily invalidate these projections, it does provide a stark look at how much curtailing our greenhouse gas emissions could change the environment in the future.