In our Eye on Earth series, we're showcasing original reporting, focusing on the health of our planet.



Greenland's melting ice sheet is contributing to a rise in sea levels that could threaten millions in low-lying areas — a situation that became more urgent this summer when 11 billion tons of surface ice melted in one day. In fact, if all of Greenland's ice sheets melted, sea levels could rise by 23 feet worldwide.



CBS News' Seth Doane flew out to Helheim Glacier, which holds enough frozen water to fill the entire state of Pennsylvania a foot deep, to meet some of the scientists on the front lines of climate change. Among them is NYU's David Holland and his wife Denise, who manages logistics.



"People say 'follow the money.' Well this is a story really of 'follow the warm water.' Water melts ice quicker than air so the ocean can melt this ice sheet much faster than the air," David explained.



Denise captured a giant piece of Helheim Glacier breaking off, or "calving," last summer. The ice chunk was so big it could stretch from lower Manhattan to midtown in New York City.



"It was huge chunks, small chucks – everything just broke apart in this one big jumble of ice," Denise said.



David Holland and the NYU team set up radar equipment that peers into the glacier to measure its movement and thickness. But the icy surface is deceiving. "So the potential problem is when we put our probes in this fjord down to the bottom and we detect large volumes of very warm, salty water," David said. "That's not sustainable."



The mayor of coastal Kulusuk, Greenland says they're feeling climate change with more ferocious storms. Nearby in the picturesque port town of Tasiilaq, Rasmus Poulsen took freelance work at a museum of Inuit culture because his winter sport adventure business had a shorter season.



"Last year was extremely good. We had a lot of snow, a lot of ice, we were able to do dogsledding into the first week in June. This year I had to close down my business for winter activities in the middle of April," Poulsen said. "Summer came very, very, very much sooner."



At the glacier, David Holland and his team have been surprised to learn just how "finicky" the atmosphere is.



"People say the climate will change by a degree or something. In the tropics I don't think that matters, but when you're at the freezing point, minus half a degree below is freezing, plus a half a degree above is melting. One degree is everything," he said.



They're collecting data to understand what is happening so scientists can then tackle the question: Why?



To hear CBS News' Seth Doane and producer Lynn Edwards discuss what it's like to report in Greenland, check out the "CBS This Morning" podcast: