What is Earth Day? 5 things to know

Today is Earth Day and more than one billion people across the globe are expected to celebrate with environmentally friendly events. Among those will be the leaders of 160 countries, who will sign the Paris Climate Agreement today.

But what exactly is Earth Day? Here's what you need to know:

When did Earth Day start?

The first Earth Day celebration took place 46 years ago, in 1970, after a devastating oil spill in America brought environmental issues to the forefront of public consciousness. According to the Environmental Protection Agency, 22 million people across the country came out in support of environmental reform.

"That day left a permanent impact on the politics of America," wrote Gaylord Nelson in the April 1980 edition of the EPA Journal. "It forcibly thrust the issue of environmental quality and resources conservation into the political dialogue of the nation.

"It showed political and opinion leadership of the country that the people cared, that they were ready for political action, that the politicians had better get ready, too. In short, Earth Day launched the environmental decade with a bang."

Since then, celebrations have only grown. This year, organizers estimate more than one billion people in 192 countries will participate in events the world over. The day is celebrated each year on April 22.

Is there a theme for Earth Day 2016?

This year, organizers are starting their four-year countdown to Earth Day's 50th anniversary by focusing on planting new trees.

"This year we are raising the stakes," the Earth Day Network, which partners with tens of thousands of organizations in 192 countries to organize Earth Day events, said in March. "Earth Day Network is pledging to plant 7.8 billion tress worldwide -- one for every person on earth.

"That's incredibly ambitious, but we believe this down-payment must be made in order to combat climate change and keep our most-vulnerable eco-systems from facing extinction."

How are people celebrating?

In Shanghai, China, people will gather today at the Okura Garden Hotel for a recycled art show, according to the Earth Day Network. In the Philippines, organizers have planned a coastal clean-up and children's storytelling hour in metro Manila. Tree plantings were scheduled for Slovenia's Golovec District, high school students in Ontario, Canada, and hundreds of other locations worldwide.

What are businesses doing?

Google marked Earth Day with a series of environmental Google Doodles by Sophie Diao. In a company blog post, she said she was inspired by the vast diversity of life on Earth.

"Our planet -- with its alternate scorching heat and bitter cold, its jagged peaks and deep trenches -- may not always be kind to its inhabitants," she wrote. "Yet somehow the flora and fauna of Earth manage to thrive. On a day like this, we remember and celebrate our home in this great and stunning ecosystem."

Apple also joined in on the celebrations, revamping its App Store to feature a variety of "Apps for Earth." The apps were created in partnership with the World Wildlife Fund. Through April 22, WWF will get 100 percent of the proceeds from the 27 apps, according to the nonprofit.

How can I get involved?

There are multiple ways to get into the Earth Day spirit, from participating in a local event to changing your bills from paper to paperless. Here are some suggestions from the Earth Day Network: