Earth Day is celebrating its 45th anniversary and has been a trending topic across the UK.
More than one billion people take part each year, the organisation claims, making Earth Day the "largest civic observance" in the world.
Although it is credited with launching the current green movement, many experts around the globe say we still face many problems.
Here are some of the reasons people are campaigning for environmental issues.

Deforestation

"We chop down 13 million hectares of forests a year - that's 36 football pitches a minute," Friends of the Earth says.
One in five people around the world relies on forests in some way for essentials such as food and fresh water.
These people include the poorest on Earth, the charity says.

Animal farming

Meat and dairy farming creates almost a fifth of the gases that lead to climate change, says Friends of the Earth.
They say this is more than the emissions from all the world's planes, cars and lorries put together.

Extinction rates

Rates of extinction not seen since the dinosaurs are currently taking place, says Friends of the Earth.
They blame factors such as logging, pollution, industrial agriculture and over-fishing.
There are now fewer mountain gorillas in the wild than footballers in the Premier League, they claim.

Coral reefs

Greenpeace says the Great Barrier Reef is under threat from Australia's coal boom and have already suffered because of things like oceans becoming more acidic and increasing in temperature.
"Around half the coral has been destroyed in the last few decades," says David Booth, professor of marine ecology at the University of Technology in Sydney.

Arctic warming

A recent study showed that Arctic sea ice had thinned by 65% between 1975 and 2012.
"The gradual disappearance of ice at the poles is having profound consequences for people, animals and plants in the polar regions, as well as around the world, through sea level rise," says Bob Ward of the Grantham Research Institute on Climate Change and the Environment at the London School of Economics.

Water pollution

About one in 10 people, around 748m across the globe, do not have access to safe, clean drinking water, Water Aid says.
Industrial waste and poor sanitation are making this scarce resource even more difficult to find and the UN has warned that the world will be plunged into a water crisis that could be crippling for hot, dry countries.

Waste management

Half of the world's population, about 3.5 billion people, do not have access to proper waste management facilities, "which can lead to significant environmental hazards", the UN says.
"Open dumping, the most prevalent waste disposal method in many countries, can lead to acute health impacts for those living closest to dumping sites, most often the urban poor," the UN Environment Programme (UNEP) explains.

American Vogue is featuring its first ever transgender model in the May issue of its magazine.
Andreja Pejic, 23, was raised in Australia, is currently dominating the runways and has modelled for Jean Paul Gaultier, Marc Jacobs, DKNY and Giles.
The transgender Serbian has modelled as both a man and a woman before undergoing gender surgery last year.
The model wrote on Instagram: "If at the beginning of my career in the modelling industry or half way through it or even this time last year you told me that I would end up having a four page feature in American Vogue I would have probably told you 'oh I dunno about that!... So you can only imagine what I'm feeling right now."
When Andreja announced she would undergo surgery last year, she told People: "I want to share my story with the world because I think I have a social responsibility… I hope that by being open about this, it becomes less of an issue."
The 23-year-old has been confirmed for Giles Deacon's show later this year and has also starred in a beauty campaign for Make Up For Ever, being the first trans-model to score a major cosmetics contract.

Worth an estimated £50m, Adele tops the under-30 rich list yet again despite not putting out any new music for more than two years.
Produced by the Sunday Times, the list looks at the top 20 richest young musicians in the UK and Ireland.
For the first time, Sam Smith has also made the list with a fortune of £12m, putting him in joint 14th place.
Completing the top six are the five boys from One Direction, including Zayn Malik who's now quit the band.
They are said to be worth £25m each.
Other rich bands include Arctic Monkeys, whose members share £45m, and Mumford and Sons, who have a combined £30m.
There are three power couples on the list.
Marcus Mumford and Carey Mulligan have £13m, Jamie Cook and Katie Downes have £12m, and Marvin and Rochelle Humes, who just make it in at number 20 on the list, have £9m.

Top 20 richest musicians under 30

1: Adele - £50m
=2: Niall Horan - £25m
=2: Zayn Malik - £25m
=2: Liam Payne - £25m
=2: Harry Styles - £25m
=2: Louis Tomlinson £25m
7: Ed Sheeran £20m
=8: Ellie Goulding £13m
=8: Jessie J £13m
=8: Leona Lewis £13m
=8: Katie Melua £13m
=8: Marcus Mumford and Carey Mulligan £13m
=8: Alex Turner £13m
=14: Jamie Cook and Katie Downes £12m
=14: Sam Smith £12m
=14 Florence Welch £12m
=17 Matt Helders £10m
=17 Olly Murs £10m
=17 Nick O'Malley £10m
20: Marvin and Rochelle Humes £9m

Tom Cruise hanging onto the side of a plane by his fingertips. A little worrying, right?
What about being responsible for one of the world's best-known film stars, 5,000 feet in the air?
Earlier this week Cruise spoke about filming the scene for the new Mission Impossible.
Actors are increasingly doing their own death-defying stunts, and Newsbeat's been talking to some of the people who help them.
Wade Eastwood, a stuntman and stunt coordinator, is responsible for keeping Tom safe.
He told Newsbeat: "When you have an actor that really wants to do it and has the ability to do it then you've got to go for it.
"The production value is in the actor always doing as much as possible," he says, "that's what the audience wants to see rather than a green screen environment or visual effects version of it. The younger audience knows the difference now. "
"You make it as safe as you can but at the end of the day you can only do so much and he has to do the rest - that's the danger and that's why audiences are going to watch."
The award-winning 44-year-old has stunt-doubled Brad Pitt, Arnold Schwarzenegger and Ewan McGregor to name a few.
For the plane stunt Wade was inside the cabin and says he was excited rather than nervous: "We'd taken care of all the things we can, safety wise".
He says it's much the same as doing his own stunts: "When I was performing the adrenaline kicks in and calms you down and you go into a surreal state where you don't remember doing the stunt.
"For me coordinating and watching someone else doing a stunt is the same thing. I've done all the preparation I can - and I go into a calm state."
Surely it's extra stressful when dealing with one of the world's biggest stars?
"Without a doubt you feel massive responsibility. With a big star there is that added pressure from a publicity point of view."
But he insists "the money doesn't come into it" and "whether it is a multimillion star or a junior stuntman, it doesn't matter to me i'ts still a life."
So no nerves for Wade. What about Tom?
None apparently: "He's very technical, he understands everything that's explained to him as a pilot - he understands aircraft."
"Tom is one for always pushing himself and pushing the action. He wants to achieve the impossible, and use the resources he has in a major feature film to make it happen.
The actor's known for doing his own stunts including throwing himself off the world's tallest building - Burj Khalifa in Dubai - in a previous Mission Impossible film.
"His ability is as good as any stuntman I have worked with in my career."
Wade says he's become good friends with Cruise.
"We share a lot of the same interests and have a lot of fun with adrenaline-filled sports after work hours," he explained.
He says that although doing the stunts is more of "a high" than coordinating them, he wasn't jealous not to be on the side of that plane.
"Well, maybe the competitive side of me was a little bit envious but then again I didn't want to be strapped to the outside of a plane in November in England."
The stunt was filmed at RAF Wittering air base and the team had to show Airbus that everything was safe before they were allowed to use the plane.
They did a test run with a dummy attached to the plane and they took precautions to prevent birds hitting it: "We put things on the plane to give Tom some kind of prevention, we did a little blast on the runway to scare the birds, had bird spotters ground and air and we had drills that Tom would do if something happened."
Earlier this week Cruise said that on one of several takes "I got hit by just a little particle" and "I literally thought it broke my ribs".
He was attached to the plane by a safety harness and "tried various things like contact lenses" instead of goggles because "he wanted to feel the effects of the wind on his eyes".
Gordon Seed has been a stuntman in the most recent Batman films, Tomb Raider and the recent Dr Who series.
Like, Wade, he also works alongside lead actors.
"Now they want the actors to do everything - they don't want stunt doubles now.
"There's a balance between seeing the artist's face and getting a nice stunt."
He's no stranger to a dangerous stunt himself - jumping 90 feet head first from a balcony for Spooks with no harness or wire (there was an airbag).
"The build up to it is quite nerve-wracking - the adrenaline's pumping, your heart's pounding. But when you actually do the stunt you are so focused on it you don't really see it, you just go through the motions you've already planted in your mind."
But he says watching someone else is a different experience.
"It's a very different sort of nerves really - it is a nervous moment - you kind of have to let your baby go at some point," he said.
"The last thing I want to do is break a lead artist. You have to be so careful. We put crash mats where we can. If it's seen to be too dangerous for them then we always double for them."
He says sometimes he has to be particularly careful. He worked with David Tennant on Dr Who, and says David was such a valuable commodity that he doubled for him most of the time.
"There's always a slim chance something could fail - but its all so rigorously tested beforehand.
"It's partly my responsibility because I've said they're fine to do it, but it would fall on the production as well because they've allowed it to happen, and there would be severe implications for the first assistant director as well.
"People get bumps and bruises all the time, but if anyone got hit in the face straight on with a baseball bat then there's been a serious mistake and something's gone wrong."
He says sometimes the most pressured situations are to do with timing and money rather than physical safety: "On a big production when they are spending thousands and thousands on a shot and you've got to get your timing just right and falling over in the right place. That can be more scary sometimes than being on fire and falling off a building.
"If your timing's out and you mess the shot up they've got to reset all the special effects and everything.
"That could be half a day and so if you mess that up you've cost them half a days shooting on your own."

The line-up for the BBC Introducing stage at Radio 1's Big Weekend in Norwich has been announced by Huw Stevens.
Five of the acts are from the event's host city and nearby areas.
Kill It Kid, Franko Fraize, Harry Edwards, Claws and Context are all from Norfolk and Norwich.
On his show last night, Huw played a track from every artist to perform and described the area as "having its own DIY, fertile music scene".
Acts that have already been confirmed for the main stage at the event on 23 to 24 May include Muse, Foot Fighters, Taylor Swift, Florence and the Machine and Years and Years.
Talking about the BBC Introducing acts to perform at Europe's biggest free-ticketed music event which takes place at Earlham Park, Huw said: "I'm particularly excited about Hot Cops, they are punk genius and Formation are one of the most thrilling bands round at the the moment."
Other acts include, Amber-Simone, Best Friends, Cash+David, Claws, Context, Fickle Friends, Franko Fraize, Get Inuit, Harry Edwards, HONNE, HUNTAR, Kill It Kid, KLOË, Laurel, Star.One, Ted Zed, The Hearts, Will Robert and Youth Club.
Three more acts will be announced on 4 May.
You can hear tracks from all the artists if you listen back to Huw's show.

The co-creator and writer of BBC One's Sherlock has told Newsbeat that it's getting harder to persuade Benedict Cumberbatch to do the show.
Steven Moffat says it's because Benedict and Martin Freeman - who plays Watson - don't need it.
They both have successful movie careers which means their schedules are packed.
"They don't need Sherlock anymore. So we have to persuade them to do it - which is fair enough," he says.
Speaking at the BAFTA Television Awards nominees party in London last night Steven Moffat says he was surprised they signed up to a fourth series.
"They are very serious about it, they do love it very much," he says.
"I didn't think we actually thought we'd get a fourth series out of them."
But he revealed this year's Christmas special has already been recorded and series four is expected at some point in the future - when it's been filmed.
Steven Moffat also writes and produces Doctor Who and says it's usual to have to persuade actors to do shows.
"You still have to pitch it. It's not unreasonable. I still sit with Matt Smith every time and Peter Capaldi and say - this is what we're going to do," he explains.
"They would like to know that we've got another bunch of stories that they would like to do. That's a fair question."
Despite being extremely busy Steven says both Benedict Cumberbatch and Martin Freeman are committed to Sherlock and enjoy filming it.
The fact that the series is shorter and relatively quick to do works in their favour too.
"It's not like doing Doctor Who where you practically marry the show," he says.
"It's round the clock, round the year and you get one day off a year and that's Christmas day and it's sodding well on on that day anyway."
"Sherlock can go on for a long time because we just show up every occasionally and do it. It's like a reunion party every time."
So is the end in sight?
"Truthfully not yet, I don't think... but then I'm an optimist."

Ben Affleck reveals the name of his slave-owning ancestor

Ben Affleck has revealed the name of his ancestor who owned a slave.
Writing on Facebook he said: "Lots of people here have been asking who the guy was.
"His name was Benjamin Cole - lived in Georgia on my mom's side about six generations back."
The actor admitted he had "regrets" about sharing his "thoughts that the issue of slavery not be included" in a US documentary about his family history.
Affleck was criticised at the weekend after leaked emails suggested he pressured a documentary-maker not to include details of slave ownership in his ancestry.
The series, Finding Your Roots, looks back into the family trees of celebrities.
Writing at the time, Broadcaster PBS denied being censored by Affleck.
The show's host, Professor Henry Louis Gates, said in a statement: "In the case of Mr Affleck - we focused on what we felt were the most interesting aspects of his ancestry - including a Revolutionary War ancestor, a third great-grandfather who was an occult enthusiast and his mother who marched for civil rights during the Freedom Summer of 1964."
In a statement on his Facebook page Affleck said: "I didn't want any television show about my family to include a guy who owned slaves.
"I was embarrassed. The very thought left a bad taste in my mouth."
He later clarified his point in the comments section.
"I see this story being framed as 'censorship' on some sites, when I told Skip I was uneasy about the slave owner, he told me he had not included it in his preliminary cut because there wasn't much detail - a name and no details, so he wasn't going with it to begin with," he wrote.
"He also told me they would do a book later with a more complete story, and I said I would be happy to participate and talk about the issues more broadly."

Kim Kardashian and Kanye West are suing the co-founder of YouTube over leaked footage of their engagement.
A California appeals court ruled the couple have "a likelihood" of winning their case against Chad Hurley, who posted the video on his new website MixBit.
Hurley argues that a confidentiality agreement that he signed was not binding.
But the couple's lawyer said his clients should be "reimbursed".
Eric George said: "By improperly advertising Mr West's and Mrs Kardashian West's intellectual property on his new website, Mr Hurley got significant value."
Hurley also claimed that he didn't leak information as the proposal was filmed for the reality show Keeping Up With the Kardashians.
But the 11-page document issued in court on Wednesday in Los Angeles said some of Hurley's claims "lack merit".
Kardashian and West's lawyers claimed Hurley broke the confidentiality agreement by posting the two-and-a-half minute video and he was "liable for claims of fraud and unjust enrichment".
The panel sitting in the hearing said: "The jury may reasonably infer fraudulent intent from these circumstances."
Hurley's lawyers have appealed, arguing that he has free speech rights.
Kanye proposed to Kim in October 2013 at San Francisco's AT&T Park while an orchestra played and family and guests looked on.
They married in May 2014 in Florence, Italy, after hosting lavish pre-wedding celebrations in France.
The couple have not stated how much money they are seeking from Mr Hurley.