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Scientists may have recorded another unsettling milestone in the buildup of carbon dioxide in Earth's atmosphere, but leave it to Oklahoma senator — and snowball aficionado — James Inhofe to find the bright side.

In a rambling broadside against the Obama administration's plans to cut carbon dioxide (CO2) emissions, Inhofe said climate "alarmists" are ignoring the positive things those emissions are doing for the world's plants.

"People don't realize you can't grow things without CO2," Inhofe, the Republican chairman of the Senate Environment and Public Works Committee, said on the chamber's floor Wednesday. "CO2 is a fertilizer. It's something you can't do without. No one ever talks about the benefits that people are inducing from that as a fertilizer." That buildup has led "to a greening of the planet and contributed to increasing agricultural productivity," he said.

The overwhelming majority of climate scientists, however, warn that the increasing concentrations of carbon dioxide and other heat-trapping gases — a byproduct of burning coal, oil, and natural gas — are changing the Earth's climate at an unnaturally rapid rate. The warming that results is likely to bring a future of rising seas and more intense storms and droughts, with the world's poor bearing the brunt of the effects.

US scientists reported this week that worldwide average carbon dioxide readings topped 400 parts per million (ppm) in March. It's the first time that threshold has been breached on a global basis, in air samples taken from 40 sites around the world, including ships at sea and isolated islands.

There hasn't been that much CO2 in the atmosphere in millions of years, researchers say, and the world was a much warmer place with much higher seas then. Scientists have said that prolonged concentrations over 350 ppm are likely to produce irreversible damage.

The March readings from the National Oceanic and Atmospheric Administration (NOAA) are the latest in a series of disturbing achievements. Readings from the Arctic, which is warming at roughly twice the rate as the rest of the globe, first topped 400 in 2012; the benchmark reading at the Mauna Loa observatory in Hawaii broke 400 in 2013.

"It's kind of depressing, but it was also expected," Pieter Tans, the leader of NOAA's Carbon Cycle and Greenhouse Gas Group, told VICE News. CO2 concentrations are not only going up, they're going up faster than ever — "and that's due to the fact that the rate of fossil fuel emissions is also at a record high," he said.

404.10 parts per million (ppm) CO2 in air 06-May-2015 http://t.co/5Q2FLbb4ix — Keeling_Curve (@Keeling_curve) May 7, 2015

There was a bright spot in 2014, when the International Energy Agency reported that emissions from energy production were flat even as the world economy grew about 3 percent. But with the world still putting out the equivalent of more than 35 billion tons of carbon dioxide each year, it will take more than a flat year or two to reverse the trend, Tans said.

"That will not stop the CO2 rise. It will slow it down, but it won't stop it," Tans said. "The longer the time frame you look at, it the more urgent it become to bring them to zero."

The milestone shows humanity needs to find alternatives to fossil fuels "as quickly as possible," Karthik Ganapathy, a spokesman for the climate-action campaign 350.org, told VICE News.

"We're not quite at the Rubicon. We're not quite at the point of no return," Ganapathy said. "But I think in the future, scientists will look back at this as an important milestone and a moment when we're really sort of knocking on danger's door in a super-direct sort of way."

Carbon dioxide concentrations rise and fall over the course of the year. As Inhofe noted, plants consume CO2, leading to lower concentrations in the summers. But the monthly averages at Mauna Loa have climbed from 315 ppm in 1958, when readings were first taken, to just over 403 in April.

With world governments hoping to hammer out emissions reductions that they hope will limit global average temperatures to a 2-degree Celsius (3.6 F) increase by 2100, a round number like 400 might help raise public awareness and galvanize support for restraining the use of fossil fuels, Ganapathy said.

"Anytime things like this happen, anytime an important threshold is crossed, anytime you have a major weather event, you bring people in," he told VICE News. But he added, "We're 350.org, and the only number we care about is getting to the number that scientists tell us is healthy and livable and sustainable — and that's 350."