400 PPM: Carbon Dioxide in the Atmosphere Reaches Prehistoric Levels

— Scientific American

On May 2, after nightfall shut down photosynthesis for the day in Hawaii, carbon dioxide levels in the atmosphere touched 400 parts-per-million there for the first time in at least 800,000 years. Near the summit of volcanic Mauna Loa—where a member of the Keeling family has kept watch since 1958—sensors measured this record through sunrise the following day. Levels have continued to dance near that benchmark in recent days, registering above 400 ppm for the first time in eons after midnight on May 7. When the measurements started the daily average could be as low as 315 ppm, already up from a pre-industrial average of around 280 ppm.

This measurement is just the hourly average of CO2 levels high in the Hawaiian sky, but this family’s figures carry more weight than those made at other stations in the world as they have faithfully kept the longest record of atmospheric CO2. Arctic weather stations also hit the hourly 400 ppm mark last spring and this one. Regardless, the hourly levels at Mauna Loa will soon drop as spring kicks in across the northern hemisphere, trees budding forth an army of leaves hungrily sucking CO2 out of the sky.

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