What everyone heartbroken over the 'Planet Earth II' turtle episode should know.

On Dec. 11, 2016, animal lovers sat in front of their TVs, devastated at what they saw on the screens in front of them.

It had to do with baby turtles.

"Planet Earth II" — the sequel to BBC's 2006 mega-hit series "Planet Earth" — had documented Hawksbill turtle hatchlings in Barbados.

The series, which aired in the U.K. and is coming to the BBC America this January, culminated in an episode focused on how cities are affecting animal populations around the world.

The Hawksbill turtle — a critically endangered species — was one of the featured creatures. And it was really tough to watch.

The series, narrated by Sir David Attenborough, explained what happens when these hatchlings are born.

When Hawksbill turtles hatch from their eggs at night, their immediate instinct is to go toward the brightest horizon, which — if humans didn't exist — would lead them to the sea (and safety).

This is a Hawksbill turtle hatchling, born in a Jakarta breeding center in 2010. Photo by Romeo Gacad/AFP/Getty Images.

But humans do exist. And our expanding societies have had a dramatic effect on this crucial point in the hatchlings' lives.

As cities continue to sprout up on seashores, their bright lights complicate those first few moments in a hatchling's life. Instead of being drawn toward the sea, hatchlings are drawn toward the artificial lights of the city. This isn't good.

Without human interference, Hawksbill turtles already have a small chance of surviving long-term, according to Carla Daniel, deputy field director of the Barbados Sea Turtle Project. But with this added barrier stopping them from safely reaching the ocean, baby turtles are getting "crushed in the road [or] lost forever in drains," among other not-so-happy endings, on their accidental journeys into the city.

It was a big wake-up call for many distraught "Planet Earth II" viewers.

The outcry among upset viewers spurred responses from the Barbados Sea Turtle Project, which partnered with the BBC during production.

"We know that watching the footage on the 'Cities' episode of 'Planet Earth II' last night was emotional and heartbreaking," the group wrote on its Facebook page. "While it does portray what thousands of hatchlings face every year, we want to reassure you that we do our very best to ensure that as many hatchlings as possible are rescued and no hatchling is ever left behind!"

Baby turtles that were hatched at a conservation center in West Sumatra are released into the ocean. Photo by Adek Berry/AFP/Getty Images.

The "Planet Earth II" team also assured viewers on Twitter that its film crew did, in fact, break protocol and saved any turtles it spotted.

Typically, the crew does everything it can not to engage or disrupt wildlife while filming, but — because this particular tragedy was manmade — they decided to intervene.

The hatchlings' fatal endings served as a learning moment for viewers on the unintended consequences of our modern existence as humans.

Many of our behaviors and technologies have surprising consequences to other species. Light pollution is a great example.

It doesn't just affect baby turtles, after all.

While light pollution may not seem as harmful as, say, pumping pollution into the air or cutting down huge swaths of trees, artificial lighting is responsible for millions of bird deaths each year, according to the International Dark Sky Association. Many birds use moonlight and starlight to hunt and migrate, and bright city lights can throw them off course. Birds may arrive in a new region too early or too late, for instance, and miss the climate conditions they need to survive there.

Photo by Frederic J. Brown/AFP/Getty Images.

Artificial lighting, which unintentionally draws insects, may create a "fatal attraction" between the tiny creatures and our manmade structures as well. Although insects seem like a nuisance to us, they're often the foundation of the food web in a given habitat. A decline in Insect population can affect whole ecosystems.  

The artificial light problem may seem unconquerable for many devastated "Planet Earth II" viewers. But the last thing we should do is give up.

Take it from Carla Daniel.

“There are many times that everything feels kind of pointless," she explained candidly of the enormous problem of hatchling deaths. "'What's the point in doing this?' This is one of those things where we kind of all have to hold hands and come together and agree to make a difference.”

“If there was one, single thing that was necessary for change, [it's] for you to get up," she noted. "Go out of your house and do something [about it]."