How the planet's climate has changed since the first Earth Day in 1970

It's been more than 50 years since the first Earth Day in the United States. On April 22, 1970, people gathered at events across the country to raise awareness about the environmental issues impacting our nation and the planet.

While the Earth Day movement has helped raise awareness about human-amplified climate change and has led to some regulatory actions, 5 1/2 decades later, the planet continues to warm at an alarming rate, with the impacts of that warming worsening with each passing decade.

Climate scientists have long recognized that increasing levels of carbon dioxide and other greenhouse gases that trap heat in the atmosphere contribute directly to global warming. There is a strong and well-established link between rising global temperatures and extreme heat events as a result of human-induced climate change.

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Since the first Earth Day, the annual average concentration of carbon dioxide in the atmosphere has increased by more than 30%. It is now rising at the fastest rate on record, according to the National Oceanic and Atmospheric Administration.

All 50 states and 240 cities across the U.S. have experienced warming since the first Earth Day, according to an analysis by Climate Central, a nonprofit climate research group. Alaska has warmed the fastest, followed by Delaware, Massachusetts and New Jersey.

The Arctic region is heating much faster than the global average, which has pushed Alaska to the top of the list, with its average annual temperature rising by 4.3 degrees Fahrenheit since 1970. Among cities, the fastest-warming over the past 55 years include Reno and Las Vegas in Nevada, El Paso and Tyler in Texas and Burlington, Vermont.

Overall, the contiguous United States is now about 2.8 degrees Fahrenheit warmer than it was in 1970, based on average annual temperatures.

Warming global temperatures are also driving sea-level rise, which has been accelerating in recent decades due to melting glaciers and ice sheets, as well as the thermal expansion of seawater as it warms.

Since 1970, sea levels have risen by more than half a foot, on average, across the contiguous United States, according to the Interagency Task Force on Sea Level Change. Some regional coastlines, states and cities have experienced even greater increases. Sea-level rise varies regionally along the nation's coastlines due to shifts in both land elevation and ocean height.

The Northeast coastline, for example, has recorded an average increase of 9 inches since 1970. Florida has seen a rise of 7 inches over the past 5 1/2 decades, while in Washington, D.C., the sea level is now 8 inches higher than in 1970.