This Day In Weather History is a daily podcast from The Weather Network, featuring stories about people, communities and events and how weather impacted them.

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On April 22, 1970, more than 20 million people marched in the streets to increase global awareness of environmental problems. That's still the largest single-day protest in history, marking the first Earth Day.

Sen. Gaylord Nelson of Wisconsin initiated Earth Day to increase ecological awareness and get the nation on the same page with the grassroots environmental movement. His ultimate goal was to get environmentalism a permanent sport on the national political agenda.

Nelson, of course, did not create this remarkable feat on his own. He worked closely with Denis Hayes, a young activist. He also enrolled non-environmentally focused partners, like Walter Reuther, a leader of the labour union United Auto Workers (UAW).

"Without the UAW, the first Earth Day would have likely flopped!" said Hayes.

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Earth Day started in the United States. Hayes grew it into a global initiative throughout the 1990s.

On Earth Day in 2016, the Paris Agreement was signed by over 120 countries. The Paris Agreement aims to keep the global temperature below 2°C. To achieve this, each country has to plan and report on what it's doing to mitigate global warming.

Now more than 195 nations partake in Earth Day.

On Earth Day's 50th anniversary in 2020, over 100 million people from around the globe observed the event, making it the internet's largest mass mobilization in history.

Nelson was awarded the Presidential Medal of Freedom to recognize his incredible work.

To learn more about the first Earth Day, listen to today's episode of "This Day In Weather History."

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