Earth Day 2000 marked the holiday’s most international celebration at that time, incorporating 5,000 different environmental groups across 184 countries. One of the highlights was a traveling drum chain that went from village to village in the Central African country of Gabon. Other notable events that year included a First Amendment Rally in Washington, D.C.

Considered to be Italy’s largest Earth Day celebration, Villaggio per la Terra is an annual five-day celebration that takes place in Rome each April. Dedicated to the preservation of the planet, the event transforms the city’s Villa Borghese gardens with cultural activities and scientific exhibitions dedicated to all things Earth Day.

Earth Day Tokyo was first celebrated in 2001 in the city’s Yoyogi Park, and has since become an annual tradition. The event features everything from food stalls — highlighted by vegetarian menu items dedicated to sustainability and eco-friendly farming — to a star-studded Earth Day Concert. The festival welcomes more than 100,000 people over its two-day run.

China's Three Gorges Dam, built across the Yangtze River, earned the title of the world's largest hydroelectric facility in 2012. The dam is 594 feet tall, 7,770 feet long, and creates the Three Gorges Reservoir — a body of water with a surface area of about 400 square miles. The renewable energy produced by the dam is enough to cover almost one-tenth of all the electricity that China requires in a year.

China's Jiuquan Wind Power Base, in western Gansu Province, isn't completed yet, but it's already the world's largest wind farm. With a planned capacity of 20 gigawatts of wind power generated from 7,000 turbines, the farm will produce enough energy to power a small country. Located on the outskirts of the Gobi Desert, the project is far larger than any other of its kind. The largest wind farm in the U.S. (and the second-largest in the world) only has 600 turbines.

The Japanese Peace Bell was gifted to the United Nations Plaza in New York City in 1954, over a decade before Earth Day was first celebrated. The bell is now rung twice annually; once on the opening day of the UN General Assembly and the other on the first day of spring at the vernal equinox, in commemoration of Earth Day.

Earth Hour began in Sydney in 2007, when 2.2 million homes and businesses shut their lights off for an hour to encourage climate change awareness. The event, sponsored by the World Wildlife Fund, has since grown to include over 50 million people across 35 countries. Earth Hour takes place in late March, one month before Earth Day.

Expo ‘74, held in Spokane, Washington, was the first world’s fair themed around the environment. Despite Spokane being the smallest city thus far to host a world’s fair, the event attracted 5.2 million visitors. After the fair closed, the site was revamped to become a public park, cleaning up a location that had been saturated with railroads and warehouses.

Pioneering landscape photographer Ansel Adams first visited Yosemite in 1916 and was transfixed by the beautiful valley. Shortly afterward, he began his interactions with the Sierra Club, becoming an official trip photographer, an outing manager, and eventually a member of its board of directors. During his time in leadership, he helped grow the organization into a powerful environmental lobbying group and used his awe-inspiring photographs to further promote the organization's causes.

The National Audubon Society's mission is to "protect birds and the places they need, today and tomorrow." The society emerged from local groups in 1901 and began its environmental work by helping to establish the first National Wildlife Refuge in the U.S. — Florida's Pelican Island. Since then, the society and its thousands of members have lobbied the government to protect birds and have altered their own personal behaviors in order to sustain a future with a healthy avian population.

The Montreal Protocol on Substances That Deplete the Ozone Layer is an agreement signed in 1987 that’s since been revised seven times and ratified by 196 nations. The protocol sought to phase out substances that led to the depletion of the ozone layer, such as CFCs and HCFCs. In turn, it lessened the ultraviolet radiation entering the Earth’s atmosphere.

Few climate activists are better known than Greta Thunberg, a Swedish environmentalist who founded the Fridays for Future movement in 2018 at just 15 years old. Thunberg skipped Friday classes to protest outside Swedish Parliament, inspiring similar strikes elsewhere. Thunberg has since delivered speeches regarding climate change at the World Economic Forum and before the United Nations.

Born more than 200 years ago, Henry David Thoreau became one of the United States' first environmentalists. His philosophies on the subject are most clearly laid out in his 1854 book "Walden," which details his experiment of living away from society on the northern shore of Massachusetts' Walden Pond. His naturalistic writing laid the foundation for modern-day environmentalism, stating, "In Wildness is the preservation of the World."

One of 63 national parks within the National Park System, Yellowstone National Park attracts around 4 million annual visitors to explore over 2.2 million acres of preserved wilderness in Wyoming, Montana, and Idaho. President Ulysses Grant executed the bill naming Yellowstone the nation’s — and the world's — first national park on March 1, 1872.

As of late 2021, California is by far the most solar-powered state in the U.S. Not only does it have one of the most ambitious renewable portfolio standards of any state, but it also gets a lot of sunlight, making such production possible. Insolation is also a factor in the rest of the highest-ranking states, which include North Carolina, Arizona, Nevada, and Texas. California, however, produces more solar energy than those other four states combined, and intends to get 100% of its energy from renewables by 2045.

According to Yale University's Environmental Performance Index, which was most recently calculated in 2020, the greenest country in the world is Denmark, followed by Luxembourg, Switzerland, and the United Kingdom. The EPI is calculated based on a variety of factors including air quality, climate change mitigation, and biodiversity. All of the ranking's top 10 countries are in Europe. The United States comes in at #24.

The Paris Agreement is an international climate change treaty to reduce greenhouse gas emissions that contribute to global warming. It was adopted in December 2015 and enforced starting the following year. As of 2023, 195 countries have signed the Paris Agreement. The long-sought pact was the culmination of meetings that began at the 1992 Earth Summit in Brazil and continued with the 1997 Kyoto Protocol.

Add the volumes of the methane, carbon dioxide, nitrous oxide, and other greenhouse gases you produce in a year, and you get your carbon footprint. The average carbon footprint for a person in the United States is 16 tons, meaning they create 16 tons of greenhouse gases in a single year. Globally, the average is closer to four tons, but in order to avoid a climate catastrophe, the average global carbon footprint has to drop to under two tons by 2050.

During his two terms as U.S. President in the early 1900s, Theodore Roosevelt used his authority to establish 150 national forests, 51 federal bird reserves, four national game preserves, five national parks, and 18 national monuments on over 230 million acres of public land. History remembers him as the country's greatest "Conservationist President," and he’s the only president to have a national park named after him.

Earth Day was first celebrated on April 22, 1970, and has since become one of the world's most popular holidays. The celebration was the brainchild of U.S. Senator Gaylord Nelson of Wisconsin, a staunch environmentalist who wanted to increase ecological awareness and "force this issue permanently onto the national political agenda." Earth Day is observed at different times around the world, but most nations celebrate it on April 22. The holiday’s message of conservation has helped spread the green movement across the globe.