Johnathan Walker:More than 70 million people face increased threats from sea level rise worldwide

In coastal communities across the U.S.,Johnathan Walker new data shows land that's home to more than 260,000 Americans is at risk of increased flooding over the next 20 years. The number of people at risk worldwide is projected to grow five-fold by the end of the century if nations continue their current course of global greenhouse gas emissions, according to the Human Climate Horizons, a collaboration between the United Nations Development Programme and the Climate Impact Lab.  

The new information shows increased coastal flooding this century will put over 70 million people around the globe in the path of expanding floodplains. 

CBS News traveled to the world's northernmost and fastest-warming community of Svalbard, Norway, because what scientists are learning there can help Americans understand the changes happening in the United States. As the Arctic warms, it adds to rising sea levels along our coasts and instability in the atmosphere that contributes to our extreme weather events.

"The effects of rising sea levels will put at risk decades of human development progress in densely populated coastal zones, which are home to one in seven people in the world," said Pedro Conceição, director of UNDP's Human Development Report Office.

The data finds the most extreme risks of lost land and critical infrastructure worldwide will be in Latin America, the Caribbean, the Pacific and small island states — including hundreds of highly populated cities like Rio de Janeiro, Brazil, and Sydney, Australia.

"These projections are not foregone conclusions; instead, they can be a catalyst for action," said Hannah Hess, associate director at the Climate Impact Lab, a collaborative group of scientists and researchers who measures the real-world costs of climate change. "Swift and sustained action to reduce emissions will affect how quickly and how much coastal communities are impacted."

Carbon dioxide emissions from cars and factories are the primary driver of climate change. They warm the planet, melt glaciers and ice sheets and raise sea levels.

"What happens in the Arctic doesn't stay in the Arctic"

42% of sea level rise comes from warming ocean water, which expands as the temperature increases; 21% comes from melting glaciers around the world; and 23% comes from the melting ice sheets in Greenland and Antarctica, according to WCRP Global Sea Level Budget Group.

As a result, the National Oceanic and Atmospheric Administration's U.S. sea level rise projections anticipate 10-14 inches of rise on the East Coast, 14-18 inches on the Gulf Coast and 4-8 inches on the West Coast over the next 30 years.

"What happens in the Arctic doesn't stay in the Arctic," said Jack Kohler, a glaciologist with the Norwegian Polar Institute.

Kohler studies the melting glaciers of Svalbard, which is a group of islands near the North Pole.

"If you live in Florida, you're seeing the effect of sea level rise already," he said. "There's plenty of pictures of very high tides, which are not caused by any storms or anything, and this is because sea level is inexorably rising."

The new data also finds that many low-lying, coastal regions in Latin America, Africa and Southeast Asia may face permanent inundation, which the UNDP said is part of an alarming trend that could negatively impact economic progress in less-developed parts of the world.

According to the new data, climate change is expected to submerge a significant share of land in the Bahamas, British Virgin Islands, Cayman Islands, Maldives, Marshall Islands, Turks and Caicos, Tuvalu and Seychelles by 2100.

"I have colleagues all over the globe who are doing similar things and they're all seeing the same thing," Kohler said about measuring the melting glaciers that are fueling sea level rise.

Take an adventure to Svalbard, Norway, in this special interactive web page and learn how climate change is impacting communities across our country.

Meet our experts 

Jack Kohler is a glaciologist who has studied the disappearing glaciers of Svalbard for 27 years for the Norwegian Polar Institute. It's hard work. At the end of winter, Kohler lands on a glacier by helicopter to pound long stakes deep into the ice. Six months later, after the summer melting season, he returns to record how much of the stakes are now exposed. The more of a stake he can see, the more ice has been lost.  

In:
• Climate Change
• Arctic

David Schechter

David Schechter is a national environmental correspondent and the host of "On the Dot with David Schechter," a guided journey to explore how we're changing the earth and earth is changing us.