[Shane] The accelerating pace of climate change here means more rain falls in the winter instead of snow.

Rain freezes, turning the ground to solid ice, making it hard for reindeer to dig for grass and lichen under the snow.

They are literally between a rock and a hard place here.

For many Sámi, the old love of reindeer herding is getting lost to the pull of the city.

There's no sign of that love disappearing here, though.

[Nils] Simba, Simba, Simba.

Simba.

Simba, Simba, Simba.

[Shane] Heh heh heh!

Simba, Simba, Simba, Simba.

[Shane] Oh, man.

[speaking Sámi] Of all the things I was expecting to come around the corner, a reindeer was not on that list.

Ha ha ha!

[speaking Sámi] [Nils, voice-over] Simba--he's like a family now.

Yeah.

He's my best friend.

[Shane] It turned out, they're pretty close.

Yeah, I love him.

[Shane] OK. Really close.

Amazing.

[Shane] He's certainly got a healthy appetite.

[speaking Sámi] [both speaking Sámi] [Shane] I'm not sure his uncle thinks this is the right place for a reindeer.

It's not just the reindeer that are changing around here.

He agrees that the climate isn't the same as it was back in the day.

Everything is changing.

I used to say if my grandfather was living now I think he would get a shock how we-- how we work with the reindeers.

[Shane] Not all the old ways have vanished.

[reindeer grunting] Nils said we should film with his wild herd... and see the power of these animals on the move.

♪ Nils works with the reindeer, herding them to find the best places to go.

♪ With Nils, we followed the animals to the edge of the forest.

This is where he wanted us to see the extent to which wild reindeer can help halt climate change.

As soon as they get amongst the young trees, the reindeer start eating the shrubs and branches.

♪ [Nils] If you see around here, here you can see reindeer eating the fresh-- the fresh sticks and also the bark from the trees.

[Shane] Just like where the foxes are fighting it out in the Canadian Arctic, here, too, the trees are advancing north, over 130 feet per year... a creeping baseline that changes the ecology of the land the reindeer rely on, and, like in Canada, the dark branches absorb the warmth of the sun and interrupt the reflective power of the white snow, accelerating climate change.

The reindeer are fighting back, trimming back shoots, keeping the advancing tree line under control.

It's a revelation in how rewilding an area can help prevent further warming.

They're eating us out of trouble.

[Nils] The reindeer are saving the Arctic here.

You don't believe me?

Ha ha ha!

Then you have to be here to see what's happening.

The--you know, the Sámi people, we live with nature, so we know what's happening because we have to have them in the nature.

It's very important, and I think a lot of people don't know that.

[Shane] The Sámi community have always known that the tundra needs the reindeer... and now scientists are starting to listen.

They measured the reflectance of the snow across Northern Europe... and they compared where the reindeer were restricted to where they were allowed to graze freely.

The effect was staggering.

Where reindeer were herded year-round, the snow reflected double the sun's radiation and warmth, keeping the ground colder and holding the snow for longer.

♪ With help from herders like Nils, the reindeer can preserve the tundra, holding back the changes here and preventing further warming.

[Nils] You know, some years, it can be very tough to be a reindeer herder, but it's something in your heart.

You know, you still work with this, you fight for this.

You--you do everything to protect the reindeer.

♪ [Shane] When nature is allowed off the leash to be fully functioning, it can have an awe-inspiring resilience.

These powers of nature shouldn't be underestimated.

If we can listen to the animals and help maintain these ice worlds they can help secure the future of our entire planet.