Environmental activists worldwide risk their lives on a daily basis to save Mother Earth - but those are the silent heroes.

Celebrities might not risk much by becoming activists, except for maybe being branded as greenwashers - but their role fighting climate change is far from meaningless. Their well-known faces - and their money - serve as standard bearers for the silent heroes' fight.

Al Gore, the 45th vice president of the United States, was a pioneer in giving voice to global warming. His campaign to educate citizens was protrayed in the 2006 film "An inconvenient truth." Nowadays, he runs the Climate Reality project, teaming up with top celebrities such as Williams Pharrel.

From DiCaprio's speech at the Oscar ceremony to Björk's eccentricities, all celebrities' actions count to fight climate change - here are some of them.

1. Leonardo DiCaprio

DiCaprio's speech at the 2016 Oscar ceremony was a decisive moment in defining him as an indisputable climate change fighter - but it did not mark the beginning of his engagement. The Leonardo DiCaprio Foundation, aimed at preserving the health and wellbeing of all of Earth's habitants, had already been set up in 1998.

"Before the Flood" is his most recent movement on climate change. In the film, the actor meets world leaders including US President Barack Obama and Pope Francis to raise awareness.

However, the actor is now facing strong criticism related to allegations of money laundering in Malaysia, and some are demanding that he step down as UN Messenger of Peace.

2. Robert Redford

This Hollywood legend was among the most acclaimed celebrities in Paris for the COP21 climate conference in 2015. The octogenarian actor has been fighting to boost clean energies and protect natural resources since the early 1970s.

In an interview with United Nations representatives, Redford stated: "I think climate change has moved up the register of issues to be considered. [...] I thought any voice that could be lent to the effort should be used, and so I'm here for that."

3. Sting

Following the request of an indigenous leader, the singer of The Police founded Rainforest Foundation International in 1989. The foundation develops rainforest protection projects around the world.

The singer took part in the People's Climate March in 2014, where he criticized Obama for not doing enough to fight climate change.

Now, at 64 years old, he is recording a new album with climate change as a major topic - one song is even "dedicated" to climate skeptics.

4. Mark Ruffalo

Off-screen, the Hulk uses his strength to support development of clean energies and fight polluting extractive methods such as fracking - he is part of the group Artists Against Fracking.

He runs the nonprofit organization Water Defense, aimed at using technology and public engagement to keep water clean.

Ruffalo has also supported other environmental campaigns, like The Solutions Project to enhance the transition toward 100 percent clean and renewable energy.

5. Björk

Together with David Bowie and Robert Plant - among other artists - Björk signed an open letter in 2015 urging international leaders to reach an agreement at the climate change conference in Paris.

"In combining our collective strengths, the creative community will amplify your commitments to positive change and strengthen the implementation of good policy decisions you make now," the artists wrote.

The eccentric has also participated in several events to fight power plants and dam projects in her home country. One thing is sure: She never goes unnoticed.

6. Jamie Oliver

"Naked chef" Jamie Oliver campaigns for sustainable farming and food sourcing in his television shows. His program "American Road Trip" is apparently the first fully carbon-neutral show on the small screen in the US.

He already counts 16 charity restaurants around the world, and is active in avoiding the discarding of hundreds of thousands of unwanted fish through by-catch.

"For me, the relationship between nutrition and the environment is one of the absolutely key issues facing our planet and our species," Oliver said to "OurPlanet," a United Nations Environment Program magazine.

7. Jack Johnson

In 2013, the surfer-songwriter set off on tour with the Guitar of Reality, a co-project with Al Gore's program Climate Reality. The guitar was built from a pine tree killed by bark beetles, a phenomenon linked with global warming.

"The Guitar of Reality means that now audiences worldwide don't just see climate change happening - they can hear it too," the Climate Reality project website reads.

Johnson has also popularized EnviroRiders, environmentally conscious guidelines for concert venues.

8. Gisele Bundchen

The Brazilian top model with German roots was awarded with the "Best Green International celebrity Award" in 2011.

Bundchen runs an eco-friendly flip-flop line to raise funds for conservation efforts in the Amazon rainforest. Together with her family, she launched the Clean Water Project to implement sustainable environmental management and help recovering the areas' vegetation.

The model was designated a Goodwill Ambassador for the United Nations Environment Program in 2009.

9. Ludovico Einaudi

Close your eyes, find peace within, imagine a pristine environment ... that was what Ludovico Einaudi and Greenpeace asked people to do - before talking about environmental destruction.

The Italian pianist played in the middle of the Arctic to highlight the perfect harmony reigning there, and the threats this is facing.

While the composer played the piece Elegy for the Arctic, international delegates were gathering at the OSPAR Commission meeting in Spain to take further steps in protecting the Arctic.

Hopefully, those beautiful notes will be remembered as a chant of hope and not as a requiem.