Atmospheric levels of carbon dioxide reached a new high in April, crossing the 400 parts per million threshold for an entire month for the first time in recorded history, NASA said Wednesday.
The observations from the Mauna Loa Observatory in Hawaii represent a 24 percent increase since NASA began gauging carbon levels at the site in 1958. The new milestone alarmed scientists who said it reflected an accelerating march toward irreversible climate change, which most scientists say is driven primarily by humans burning greenhouse gas-emitting fossil fuels.
“Passing the 400 mark reminds me that we are on an inexorable march to 450 ppm and much higher levels. These were the targets for ‘stabilization’ suggested not too long ago. The world is quickening the rate of accumulation of CO2, and has shown no signs of slowing this down. It should be a psychological tripwire for everyone,” said Michael Gunson, global change and energy program manager with NASA.
Climate scientists consider 450 ppm a critical line for the climate. Keeping atmospheric concentrations below that mark gives nations a reasonable shot at keeping global temperatures from rising 2 degrees Celsius above preindustrial levels by 2100. Anything above that could bake in the effects of climate change, they say.
Nations will attempt to strike an agreement to govern emissions beyond 2020 at United Nations negotiations in December in Paris in hopes of keeping temperatures below the target. But many scientists are skeptical that negotiators and their governments can make enough commitments to avoid that outcome.
