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The Earth's atmosphere is more saturated with greenhouse gases now than at any other time in human history. For the first time on record, the average amount of carbon dioxide -- the main long-lived gas responsible for global warming -- in the air passed 410 parts per million (ppm) for an entire month.

Data collected at the Mauna Loa Observatory in Hawaii had already shown carbon dioxide readings that temporarily exceeded that threshold for a time in 2017 but not for a whole month. The new data collected for the month of April and released on May 2, underscore how quickly carbon dioxide levels continue to rise despite global attempts to reduce emissions.

The new record demonstrates that despite gains made in renewable energy and energy efficiency, heat-trapping greenhouse gases continue to build in the atmosphere, altering the odds and intensity of many extreme weather events, causing sea levels to rise, and a myriad of other effects.

"We know exactly where that CO2 is coming from, and we're pretty clear on what it does," said Kate Marvel, a climate scientist at NASA's Goddard Institute for Space Studies, in an email.

"Combustion -- the chemical reaction we use to generate most of the energy we use -- gives off CO2 as a byproduct. We've been doing a lot of combusting since the Industrial Revolution, and all that extra CO2 has to go somewhere. Essentially, we've been treating the atmosphere as a dumpster for over 150 years."

Because of its molecular structure, carbon dioxide is a greenhouse gas- it traps the heat given off by our planet and makes it warmer.  And, in fact, the global average temperature has risen about 2 degrees Fahrenheit since the 19th century.  This long-term warming is entirely due to human activities.  Our CO2 emissions are changing the planet we all live on, and we're not slowing down.

The average concentration of carbon dioxide in the atmosphere was 410.31 ppm for the month of April, according to the Mauna Loa readings.

What's especially shocking to climate scientists is that the 410 ppm mark is a 30 percent increase in carbon dioxide since these measurements began. In 1958, carbon dioxide levels were at just 315 ppm. At the beginning of the Industrial Revolution, carbon dioxide amounts were even lower, at about 280 ppm.

Due to greenhouse gas emissions from burning fossil fuels and chopping down forests, among other sources, the first time the curve exceeded the 400 ppm level was in 2013.

These numbers may seem abstract, but they have immense implications for life on Earth as we know it.

Carbon dioxide levels never exceeded 300 ppm at any point in the past 800,000 years, according to the Scripps CO2 Program, which funds the Mauna Loa observations.

"As to why the continued growth... is so alarming, it is because it is a continued indicator that we are conducting an inadvertent and unprecedented experiment with our planet, the only home we have," Katharine Hayhoe, climate scientist at Texas Tech University said via email.

"It’s as if we discovered that something we eat every day is causing our body to run a fever and develop all kinds of harmful symptoms — and instead of cutting back, we keep on eating it. If that isn’t alarming, I don’t know what is.”

Paleoclimate records from tree rings, coral reefs, ocean sediment, ice cores, and other sources indicate that, in the distant past, when carbon dioxide levels were about as high or higher than they are today, the global average temperature soared and seas were more than 66 feet higher than they are now.

Climate scientist Michael Mann of Penn State University said the 410 ppm milestone is a sobering one. "We probably have to go back 5 to 10 million years at least to find a time when CO2 levels were naturally that high," he said.

"So we are indeed playing an unprecedented, uncontrolled experiment with the one planet in the universe we know that can support life."

On our current path, it's likely that the atmosphere will reach 450 to 500 ppm by the end of the current century, a level that climate scientists have found would trigger potentially disastrous consequences.

One such danger lurks in the planet’s ice sheets, which could melt rapidly, causing seas to rise faster than society can readily and cost-effectively adapt.

"... The global average temperature has risen about 2 degrees Fahrenheit since the 19th century," said NASA's Marvel. "This long-term warming is entirely due to human activities. Our CO2 emissions are changing the planet we all live on, and we're not slowing down."

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