In the crazy world of showbusiness, it's quite easy for celebrities to get wrapped up in their own affairs and forget about the world going on around them.
But here are six famous faces who've used their fame to draw attention to some of the big issues facing our planet.
1. Leonardo DiCaprio
DiCaprio chose to use his long-awaited moment on stage at the Oscars to talk about global warming, which was something he'd experienced first hand during the making of his film The Revenant. "Our production needed to move to the southern tip of this planet just to be able to find snow," he said in his speech.
2. Livia Firth
Oscar-nominated Ruffalo sent a stern message straight to Number 10 in February this year warning David Cameron against the "legacy mistake" he was making with fracking. A vocal campaigner for leaving fossil fuels in the ground in the US, he brought his message across the pond and asks: "What is a politician if he's not credible?"
4. Emma Thompson
Leading actress Thompson is a prolific Greenpeace campaigner who doesn't mince her words. She sailed all the way to the Arctic to prove to world leaders that ice is disappearing, and claimed that if we think the refugee crisis is bad now, it will only get much worse when parts of the Earth become uninhabitable due to climate change.
5. Gisele Bundchen
Brazilian supermodel Bundchen launched her own collection of eco-friendly Ipanema flip flops - and then used her line to raise money for conservation of the Amazon rainforest after visiting and being shocked by the devastation caused by deforestation.
6. Gary Neville
From being the founder of the Sustainability in Sport initiative to helping design his own futuristic underground 'eco house' in Lancashire, Gary Neville has done his fair bit to champion environmental efficiency. So much so that University of Salford awarded him an honorary degree in recognition of his work in 2014.