While stricter emissions standards for cars are slowly starting to take effect, the amount of carbon dioxide in the atmosphere continues to rise.
Levels of atmospheric carbon dioxide--a greenhouse gas that contributes to climate change--of more than 402 parts per million (ppm) were recorded last month by monitoring equipment atop a Hawaiian mountain.
That's the highest recorded level ever, and it was logged earlier in the year than was last year's high. The new levels, uncharted territory for humans, were noted by Mashable.
The data came from the daily record of atmospheric carbon dioxide maintained by Scripps Institution of Oceanography at the University of California--San Diego
A level of 400 ppm--or 0.04 percent--was recorded in mid-May last year, but the fact that the new record level was recorded so early indicates that the annual CO2 peak--typically occuring in mid- to late May--will be higher than last year's.
Concentrations were at 313 ppm when observation equipment first began recording CO2 levels atop Hawaii's Mauna Loa volcano in 1958,
The chart documenting the rise in CO2 concentrations is known as the Keeling Curve, after the founder of the CO2 monitoring program, Scripps Institution of Oceanography scientist Charles David Keeling.
An increase to 402.20 ppm was recorded April 7, while the National Oceanic and Atmospheric Administration (NOAA) showed a slightly lower level of 402.11 ppm.
There is no scientific consensus on when CO2 levels were last this high. But estimates range from 800,000 years ago to 15 million years ago, based on analysis of air bubbles recovered in ice cores from Antarctica.
The Earth has experienced higher CO2 levels before, but they were caused by environmental factors, including variations in the planet's orbit and solar-energy output.
At those times, however, there weren't 7 billion human animals on the planet either.