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.