Hawaii's Mauna Loa's Observatory just captured an ominous sign about the pace of global warming.

Atmospheric levels of planet-warming carbon dioxide aren't just on their way to yet another record high this year - they're rising faster than ever, according to the latest in a 66-year-long series of observations.

Carbon dioxide levels were 4.7 parts per million higher in March than they were a year earlier, the largest annual leap ever measured at the National Oceanic Atmospheric Administration laboratory atop a volcano on Hawaii's Big Island. And from January through April, CO2 concentrations increased faster than they have in the first four months of any other year. Data from Mauna Loa is used to create the Keeling Curve, a chart that daily plots global atmospheric carbon dioxide concentration, tracked by Scripps Institution of Oceanography at the University of California at San Diego.

For decades, CO2 concentrations at Mauna Loa in the month of May have broken previous records. But the recent acceleration in atmospheric CO2, surpassing a record-setting increase observed in 2016, is perhaps a more ominous signal of failing efforts to reduce global greenhouse gas emissions and the damage they cause to Earth's climate.

"Not only is CO2 still rising in the atmosphere - it's increasing faster and faster," said Arlyn Andrews, a climate scientist at NOAA's Global Monitoring Laboratory in Boulder, Colo.

A historically strong El Niño climate pattern that developed last year is a big reason for the spike. But the weather pattern only punctuated an existing trend in which global carbon emissions are rising even as U.S. emissions have declined and the growth in global emissions has slowed.

The spike is "not surprising," said Ralph Keeling, director of the CO2 Program at Scripps Institution, "because we're also burning more fossil fuel than ever."

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Why carbon dioxide levels keep rising

Carbon dioxide levels naturally ebb and flow throughout each year. At Mauna Loa, they peak in April and May and then decline until August and September. This follows the growth cycle of northern hemisphere plants: growing - and sequestering away carbon - during the summer months and releasing it during fall and winter as they die and decompose.

Once CO2 makes it into the atmosphere, it stays there for hundreds of years, acting as a blanket trapping heat. That blanket has been steadily thickening ever since humans turned materials that were once dense stores of carbon - oil and coal, primarily - into fuel to burn.

That means the Keeling Curve reaches new heights each May, forming a new peak in a sawtooth-like pattern.

The chart originated when Charles David Keeling, Ralph Keeling's father, started recording atmospheric concentrations of CO2 atop the Mauna Loa volcano in the late 1950s. It was the first effort to measure the planet-warming gas on a continuing basis and helped alert scientists to the reality of the intensified greenhouse effect, global warming and its impact on the planet.

Each annual maximum has raised new alarm about the curve's unceasing upward trend - nearing 427 parts per million in the most recent readings, which is more than 50 percent above preindustrial levels and the highest in at least 4.3 million years, according to NOAA. Atmospheric CO2 levels first surpassed 400 parts per million in 2014. Scientists said in 2016 that levels were unlikely to drop below that threshold again during the lifetime of even the youngest generations.

Since that year, carbon dioxide emissions tied to fossil fuel consumption have increased 5 percent globally, according to Scripps.

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Why annual increases vary

The increase in carbon dioxide from year to year is not precisely consistent. One factor that tends to cause levels to rise especially quickly: the El Niño climate pattern.

El Niño is linked to warmer-than-average surface waters along the equator in the eastern and central Pacific. That warmth affects weather patterns around the world, triggering extreme heat, floods and droughts.

The droughts in particular contribute to higher-than-normal spikes in atmospheric carbon dioxide, Keeling said.

Tropical forests serve as reliable stores of carbon because they don't go through the same seasonal decay as plant life at higher latitudes. But El Niño-linked droughts in tropical areas including Indonesia and northern South America mean less carbon storage within plants, Keeling said. Land-based ecosystems around the world tend to give off more carbon dioxide during El Niño because of the changes in precipitation and temperature the weather pattern brings, Andrews added.

That can allow CO2 concentrations to rise especially quickly on the tail end of El Niño events - such as the current one, which NOAA scientists said Thursday is likely to end this month.

The increase observed at Mauna Loa over the past year is some five times larger than the average annual increases seen in the 1960s, and about twice as large as in the 2010s, according to NOAA data.

A record surge in early 2016 was also at the end of a historically strong El Niño.

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Why carbon matters

It will take some four decades to stop the annual growth in CO2 concentrations, even if all emissions began declining now, Andrews said. Because Earth's carbon cycle is so far out of its natural equilibrium, plants, soils and oceans would give off stores of extra CO2 in response to any reduction in humans' emissions, she said.

And for CO2 concentrations to fall back below 400 parts per million, it would take more than two centuries even if emissions dropped close to zero by the end of this century, she added.

In the natural carbon cycle, the element passes through air, soil and water, and plants and animals, eventually making its way into deep ocean sediments and fossils deep underground. Carbon's movement throughout Earth systems helps regulate our planet's temperatures - unlike on Venus, for instance, where CO2 accounts for most of the atmosphere, making that planet's surface hellishly hot.

But human emissions of CO2 throw that system out of balance. It's like adding more and more trash to a dump, Andrews said. Even if each load of trash gets smaller, "it's still piling up."