Earth Day and the birth of US environmental monitoring

Whilst it may seem a rather inconsequential date in the calendar, the creation of Earth Day marked the beginning of much that we take for granted in environmental monitoring. 

By Jed Thomas 

Every April 22nd, Earth Day is celebrated in more than 190 countries, making it a candidate for the largest secular civic event in the world.  

Yet for all its global reach, Earth Day began with a simple but radical idea: that the environment mattered, and that millions of people demanding change at once could force the world to listen. 

Since that first day in 1970, Earth Day has become more than a date on the calendar, it’s become a historical inflection point.  

Not only did it launch the modern environmental movement, but it also laid the political and scientific groundwork for one of the most critical components of environmental protection: long-term, large-scale environmental monitoring. 

For professionals working in the field, whether analysing rainfall chemistry, installing air quality sensors, or translating data into policy, the legacy of Earth Day is not abstract. 

It’s alive in the systems we maintain, the technologies we advance, and the commitment to evidence that underpins everything we do. 

What is Earth Day? 

Earth Day was born out of growing public concern over pollution, ecological destruction, and the visible environmental crises of the 1960s: the Cuyahoga River catching fire, choking smog in major cities, pesticide-related wildlife die-offs, and oil spills like the massive 1969 blowout off the coast of Santa Barbara. 

Senator Gaylord Nelson of Wisconsin, inspired by the anti-war teach-ins of the era, proposed a national day of environmental education and protest.  

With grassroots organizing led by then-25-year-old Denis Hayes, the first Earth Day on April 22, 1970, mobilized an estimated 20 million Americans, 10% of the U.S. population at the time. 

This massive public outpouring of concern translated almost immediately into political action.  

By the end of 1970, the U.S. Environmental Protection Agency (EPA) had been established, and Congress had passed the Clean Air Act, followed by the Clean Water Act and Endangered Species Act in subsequent years.  

These laws didn’t just impose restrictions, they created obligations to measure pollution and track progress. 

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How did environmental monitoring in the US start? 

From the very beginning, Earth Day catalysed a belief that environmental problems needed scientific solutions.  

It marked a shift in how environmental protection was approached, not just through protest or regulation but through data. 

Many of the United States’ foundational monitoring programs still in use today were born in the aftermath of Earth Day: 

The National Atmospheric Deposition Program (NADP) was created in 1977 to track acid rain and other forms of atmospheric deposition, becoming a cornerstone of air quality science. 

The EPA’s AIRNow and CASTNET programs grew from earlier regional efforts to monitor ground-level ozone, sulphur dioxide, nitrogen oxides, and fine particulates. 

The National Water Quality Monitoring Council and other state-level initiatives emerged to assess the health of lakes, rivers, and estuaries across the country. 

Without these systems, there would have been no reliable way to prove the effects of pollution, evaluate policies, or measure recovery.  

The environmental wins often attributed to Earth Day’s legacy were inseparable from the ability to monitor change. 

Early successes

The big achievements of the last five decades are well known. What’s less well known is how central monitoring was to each one. 

Acid rain reduction  

In the 1980s, widespread monitoring showed rain in the northeastern U.S. was up to ten times more acidic than normal.  

This data galvanized political action, leading to the Clean Air Act Amendments of 1990, which imposed a cap-and-trade system for SO₂.  

Follow-up monitoring confirmed dramatic declines in acidity, up to 85% in some regions, and partial recovery in damaged ecosystems. 

Closing the hole in the ozone 

Earth Day helped fuel public understanding of invisible environmental threats.  

After the discovery of the Antarctic ozone hole in the 1980s, atmospheric monitoring systems worldwide tracked the role of CFCs in ozone depletion.  

This scientific clarity paved the way for the Montreal Protocol, one of the most successful international environmental treaties to date. 

Cleaner air in American cities  

Thanks to long-term air quality monitoring, we know that levels of lead, carbon monoxide, and sulphur dioxide in U.S. cities have dropped dramatically since the 1970s. 

These changes correspond directly to policy interventions and to the data that justified them. 

The foundations of climate monitoring  

From Mauna Loa’s continuous CO₂ record to satellite-based Earth observation systems, many of the climate data streams used today can trace their funding and public relevance back to the political and cultural shift sparked by Earth Day.

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What Earth Day means for contemporary environmental monitoring 

55 years on, Earth Day remains relevant. The threats we face today are more complex: climate disruption, biodiversity loss, PFAS contamination, microplastics, and more. 

Monitoring these emerging problems requires new tools, broader networks, and smarter integration of data across disciplines. 

Yet the infrastructure built in the wake of Earth Day is under pressure.  

Federal budget cuts, regulatory rollbacks, and politicised scepticism toward science have put many long-running monitoring programs at risk.  

A decades-long rainwater acidity study, for instance, recently lost federal funding, even as new acidification risks re-emerge. 

At the same time, advances in technology, like low-cost sensors, real-time data platforms, and citizen science apps, offer new possibilities.  

Monitoring professionals today are tasked with balancing rigor and accessibility, continuity and innovation. 

And in a world increasingly shaped by human impact, the role of the environmental monitoring professional is more vital than ever. 

So, on this Earth Day in 2025, remember: the story of environmental protection is also the story of measurement. And Earth Day helped make both possible. 

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