Atmospheric carbon dioxide hit a new record in April , averaging about 431 parts per million at NOAA's Mauna Loa Observatory. That's up from under 320 ppm when the site began measurements in 1958. Scientific American reports: Greenhouse gases, such as carbon dioxide, are measured as a proportion of the total atmosphere. The numbers are presented as the number of molecules of a particular gas out of a million total molecules, or ppm. Climate scientist Zachary Labe of Climate Central, a nonprofit that researches climate change, says the new record is "depressing" but not unexpected. "It's just another sign that carbon dioxide continues to increase in our atmosphere as our planet continues to warm," he says. "For many climate scientists, this is just 'here it is again, another record in the wrong direction.'"

Labe explains that the amount of CO2 in the atmosphere tends to peak in April each year as decaying plants release greenhouse gases after winter.…