ADRIAN FLORIDO, HOST:
Around the world today, many people are marking Earth Day, calling for urgent action to reverse catastrophic climate change. It isn't just about protecting the planet for humans, of course.
(SOUNDBITE OF WHALES VOCALIZING)
FLORIDO: That's a North Atlantic right whale. They're highly endangered. And several years ago, they disappeared from the waters off the coast of Maine, where they're normally found. Now scientists are linking that to mysterious changes that begin thousands of miles away. Lauren Sommer from NPR's Climate Desk takes us there.
LAUREN SOMMER, BYLINE: On a warm summer day, the surface of Greenland is alive.
ANDREW SOLE: So this water is just coming from the surface of the ice sheet, which is melting all the time. So we saw lower down...
SOMMER: Andrew Sole is a researcher at the University of Sheffield. We're in west Greenland, and there's ice as far as we can see. It forms craggy peaks, deep crevices, and it's all liquefying.
SOLE: The meltwater gathers, forms little rivulets, little streams, and they all feed into a main river.
SOMMER: A river on top of the ice. And that river suddenly disappears. It drops into a dark, somewhat terrifying crack in the ice - basically, a hidden waterfall.
SOLE: Now, where it's going is to the bed of the ice sheet.
SOMMER: Greenland is melting more and more as the climate gets hotter. It's losing 280 billion tons of ice a year. And that melt is going to speed up. But by how much? That's what Sole is here studying.
SOLE: What is it, 200 milliliters?
UNIDENTIFIED PERSON: Yeah.
SOLE: Two hundred milliliters. OK, go for it, Ryan.
SOMMER: His research team is tracking this meltwater by releasing a colorful nontoxic dye.
SOLE: So now the whole river downstream of Ryan has turned a really fluorescent bright pink. And it's, to be honest, quite a surreal sight, surrounded by the lovely white ice and the sort of blue turquoise color of the water.
SOMMER: This meltwater pours to the bottom of the ice sheet and flows underneath it, building up the pressure.
SOLE: What happens under the ice is that water pressure is sufficient to lift the ice or to reduce the friction at the base of the ice to speed it up.
SOMMER: That means the ice sheet moves faster at certain times of year, sliding towards the Atlantic Ocean. And that's where it can have huge consequences. Greenland is at the crux of a crucial ocean current, one that controls what it's like in the ocean and on land. It's called the Atlantic Meridional Overturning Circulation, or AMOC for short.
AMY BOWER: The AMOC has been depicted as a conveyor belt.
SOMMER: Amy Bower studies ocean currents at the Woods Hole Oceanographic Institution. Here's how this giant ocean conveyor belt works. The current carries warm water from the equator up the East Coast of the U.S., all the way to Greenland. That's where the salty water cools off. It gets heavy and sinks to the bottom of the ocean.
BOWER: And then go back towards the equator, down deep, carrying that cold water, kind of a return flow.
SOMMER: This giant conveyor belt can carry more water than 8,000 Mississippi Rivers, and it's powered by that sinking that happens near Greenland. But that's also where more freshwater is pouring into the ocean from all that melting ice.
BOWER: Freshwater is like, I don't want to sink. I don't want to sink. I'm very light (laughter). I don't want to sink. So fresh water tends to inhibit this sinking motion.
SOMMER: If the sinking gets weaker, the whole ocean current could slow down. There are signs that's already happening, though some scientists say it needs to be studied longer to be certain. And when currents change, it can cascade through the whole ocean.
It's late summer and scientist Philip Hamilton is searching for North Atlantic right whales.
PHILIP HAMILTON: It's our fourth night at sea. It's been a challenging trip so far.
SOMMER: He knows most of the whales individually by name. That's because there are only 340 of them left. And for decades, he's tracked them with a team from the Anderson Cabot Center for Ocean Life.
HAMILTON: We've only been able to find about 20 whales in this large area, and we're expecting to find more like 70 or 80.
SOMMER: Normally, Hamilton would be on the water in the Gulf of Maine during the summer, but around 2015, the whales began disappearing from there. Now he's looking hundreds of miles away in Canadian waters, where some of the right whales have turned up.
HAMILTON: We saw a calf, appears to have a propeller cut on its chin after only eight months of life. Pretty distressing.
SOMMER: Over a two-year period, 21 right whales were killed in Canada, many hit by ships or tangled in ropes from fishing gear. There were no protections for the whales because no one was expecting them there. But the whales needed to move because they were following their food.
ERIN MEYER-GUTBROD: I usually just call them bugs, and I think of them as bugs in the water.
SOMMER: Erin Meyer-Gutbrod is an ecologist at the University of South Carolina. She's talking about a tiny plankton called calanus finmarchicus. Right whales used to feed on them in the Gulf of Maine, but the water there is getting hotter because of shifting ocean currents. It's the kind of change scientists say could only get worse as Greenland keeps melting.
MEYER-GUTBROD: The Gulf of Maine is warming faster than 99% of the global ocean.
SOMMER: The plankton declined, so whales had to search for them in new places. The Canadian government recently started closing fishing grounds when whales are around to protect them, but they're still dangerously close to extinction, especially as the oceans keep changing.
MEYER-GUTBROD: Which puts us all in this state of emergency because then we don't really know where they're going to go, which means that we can't effectively protect their habitat.
SOMMER: Meyer-Gutbrod says it's not just whales at risk. Changing ocean currents could cause entire ecosystems to shift or die off.
MEYER-GUTBROD: We're just entering this time of extreme uncertainty. You know, we can't look at the past and allow that to shape the future because humans have kind of thrown a wrench in what used to be natural processes.
SOMMER: She says one hope for the whales and the rest of the ecosystem is to protect them by predicting these changes ahead of time, to know what might happen. And to do that, scientists need to better understand how climate change could be setting off this cascade, from hotter oceans to shifting ocean currents and, ultimately, to how a huge hunk of ice sitting on top of Greenland is disappearing increasingly fast.
Lauren Sommer, NPR News.
FLORIDO: NPR's Climate Desk is looking at the far-reaching effects of melting ice all this week. You can catch more of their stories right here or online at npr.org/icemelt. Transcript provided by NPR, Copyright NPR.
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