Wednesday marks the 50th anniversary of Earth Day, when an estimated one billion people around the world take part in the annual day of environmental action, believed to be the largest secular observance on the planet.

This year’s plans for massive in-person events have been upended by the coronavirus pandemic but the movement has pivoted to 24-hours of digital action including speakers like Christiana Figueres, architect of the 2015 Paris Climate Accords, Al Gore and Zac Efron along with performances and digital "teach-ins".

The theme for this year is climate action, with 2020 seen as a tipping point for action on reducing greenhouse gas emissions and achieving the UN goal of keeping global warming below 2C.

The Independent takes a look back at Earth Day over half a century.

1970

Decades of lead gas in vehicles and industries operating with little regard for environmental consequences had taken its toll on America's air, land and water pollution. The 1962 book Silent Spring, by Rachel Carson, set the stage for the movement to come, selling half a million copies and highlighting the devastating impact of pollution on the natural world.

The first Earth Day came about after Senator Gaylord Nelson witnessed the impact of an oil spill in Santa Barbara, California in 1969 and wanted to harness the energy of the youth-driven, anti-Vietnam War movement into environmental action.

A short meeting with a graduate student, Denis Hayes, led to Sen Nelson recruiting him to organise “teach-ins” on college campuses which expanded into nationwide events, encompassing a myriad of groups along with students. The name Earth Day was adopted and sparked the national consciousness: Twenty million Americans, 10% of the population at the time, demonstrated from coast to coast on April 22, 1970.

Speakers at events included the Beat poet Allen Ginsburg and activist and future presidential candidate Ralph Nader; the Broadway cast of musical Hair and Native American band Redbone performed in Philadelphia. In New York, Fifth Avenue was closed to traffic from Union Square Park to Central Park for demonstrations.

The ragtag gatherings and community events had a serious impact. Following Earth Day, President Richard Nixon established the Environmental Protection Agency and in the years that followed, environmental legislation including the Clean Water, Clean Air and the Endangered Species Act, among others, were introduced.

1990

The Nineties saw Earth Day go global with events held in 141 countries, involving 200m people. Events took on a more sophisticated air with a $3m budget and increased TV and radio coverage. The movement also inspired an increase in recycling efforts and paved the way for the 1992 UN Earth Summit.

2000

The millennium brought a new urgency to the environmental movement with focus on the looming crisis of global warming and the urgent need to switch to clean energy sources. Hundreds of millions of people became involved in 184 countries, building grassroots movements. The internet began to play a significant role in organising and hundreds of thousands marched on the National Mall in DC for a First Amendment Rally.

2010

The Earth Day Network launched a campaign to plant a billion trees and achieved the goal two years later. The decade also saw the historic Paris Climate Accords, signed by leaders from 175 countries in 2016, with a goal of halting global warming to 2C above pre-industrial levels.

2020

This year is viewed as a crucial inflection point in the fight against climate change as scientists warn we have little more than a decade to make a difference to our warming planet.

The Covid-19 pandemic has prevented the planned in-person mass demonstrations and instead a digital gathering, Earth Day Live, will broadcast for 24 hours to an expected one billion people in more than 190 countries.

Founder Denis Hayes acknowledged the impact that the "Black Swan" event of the coronavirus has had on this year but encouraged US demonstrators to see this coming presidential election day in November as another Earth Day.

He wrote in the Seattle Times: "But understand that the real challenge lies in the next six months. The 2020 US election will be the most important of your lifetime. It can be an inflection point for the world.

"The 2020 election will determine whether the great American experiment — universal suffrage, separation of powers, Bill of Rights, rule of law — will be resuscitated from the dark impact of the worst president in the nation’s history."

He added: "The 2020 election will determine whether America will come again to cherish sound science, respect expertise, revere innovators and assume its leadership role in protecting the planet from climate devastation. Essentially, all climate scientists agree that we are approaching irreversible tipping points that threaten to permanently impoverish not just the human prospect but the entire web of life."

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