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Image: Creative Commons

Image: Creative Commons

The average atmospheric concentration of carbon dioxide stayed above 400 parts per million throughout March 2015, according to the National Oceanic and Atmospheric Administration (NOAA). This is the first time this has happened in recorded history.

Carbon levels first hit 400 ppm in the Northern Hemisphere last May. While the atmospheric concentration of carbon dioxide has been on an upward course since the Industrial Revolution, this was the first time in human history that it touched that hazardous threshold. Ice cores recovered from the East Antarctic show that the atmosphere hasn’t been packed with that much carbon since at least 800,000 years ago, and possibly not for the last 15 million years.

The dashed red line with diamond symbols represents the monthly mean values, centered on the middle of each month. The black line with the square symbols represents the same, after correction for the average seasonal cycle. (Image Credit: NOAA)

The dashed red line with diamond symbols represents the monthly mean values for carbon levels, centered on the middle of each month. The black line with the square symbols represents the same, after correction for the average seasonal cycle. (Image Credit: NOAA)

Since May 2014, the ppm has hovered around 400 in the Northern Hemisphere, but March 2015 was the first time it stayed above that level for the entire month.

Ralph Keeling, director of the CO2 program at the Scripps Institution of Oceanography, called last year’s benchmark “a wake-up call about how much we’ve already changed the atmosphere.”

While the chemical makeup of the Earth’s atmosphere does change over time, the rapidity of the current carbon buildup is almost incontrovertible proof that humans are affecting the mix. According to Pieter Tans, lead scientist of NOAA’s greenhouse gas network, half of the rise in atmospheric CO2 has occurred since 1980.

On Wednesday, he told The Guardian that humans have raised carbon concentrations more than 120 ppm since pre-industrial times.

“This may not be our climate rubicon, but we’re certainly standing on the shores of disaster,” Jamie Henn, co-founder and communications director for the advocacy group 350.org, told The Huffington Post. “400 ppm is well past the point of safety which many scientists put at 350 ppm.”

This milestone will serve as a salient warning to environmental policymakers as they prepare for the major climate summit that will take place in Paris this December. Higher concentrations of greenhouse gases in the atmosphere will likely push average global temperatures above two degrees Celsius by the end of this century, a threshold that will have major consequences for both developed and developing nations.

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