The monthly peak amount of carbon dioxide in the Earth's atmosphere in 2019 jumped by a near-record amount to reach 414.8 parts per million (ppm) in May, which is the highest level in human history and likely the highest level in the past 3 million years.

Why it matters: Carbon dioxide is the most important long-lived greenhouse gas, with a single molecule lasting in the air for hundreds to around 1,000 years. The continued buildup of carbon dioxide due to human activities, such as burning fossil fuels for energy, is driving global temperatures up and instigating harmful impacts worldwide.

The fact that carbon dioxide levels increased by a near-record amount of 3.5 ppm in just one year illustrates that we're headed in the opposite direction from what climate scientists have shown is needed to avoid the worst consequences of global warming.

Details: According to Scripps Institution of Oceanography, the average carbon dioxide concentration in the atmosphere recorded at the isolated Mauna Loa Observatory in Hawaii averaged 414.8 parts per million during May, which is the highest seasonal peak since such observations began 61 years ago.

The highest monthly mean carbon dioxide value typically occurs in May, before plants take in large amounts of greenhouse gases during the Northern Hemisphere growing season.

The National Oceanic and Atmospheric Administration operates a worldwide greenhouse gas observational network, and its data was close to Scripps' May year-to-year data.

By the numbers:

Readings from NOAA show a seasonal peak of 414.7 ppm, and the second-fastest rate of increase in any year on record.

Studies using ice cores and other data on historical carbon dioxide levels show this is unprecedented in all of human history, and likely the highest amount of CO2 in the air during the past 3 million years.

The 2019 peak was 3.5 ppm higher than the 2018 monthly peak, which was the second-highest annual jump on record.

This continues a 6-year streak of steep global increases in carbon dioxide concentrations.

The rate of increase has quickened in recent decades, going from about 1.6 ppm per year in the 1980s to 2.2 ppm per year in the past decade, a trend conclusively tied to human activities.

Monthly CO2 values at Mauna Loa first breached the 400 ppm threshold in 2014.

Part of the increase since 2018 is thought to be related to an ongoing El Niño event in the tropical Pacific Ocean.

The big picture: Scientists have warned that if the world is to limit global warming to 1.5°C, or 2.7°F, above pre-industrial levels, then sharp emissions cuts have to begin in the next few years, with the world headed for negative emissions by the end of the century.

Background: In the northern fall, winter and early spring, plants and soils give off CO2, which cause levels to rise through May.

What they're saying: "These are measurements of the real atmosphere," says Pieter Tans, senior scientist with NOAA’s Global Monitoring Division, in a press release. "They do not depend on any models, but they help us verify climate model projections, which if anything, have underestimated the rapid pace of climate change being observed."

What's next: Scientists will announce a new annual figure for 2019 in early 2020, but the monthly peak is considered to be an important climate indicator.

Go deeper: Earth's carbon dioxide level slips past another ominous milestone