May 21, 2013

The global concentration of carbon dioxide in the atmosphere – the primary driver of recent climate change – has reached 400 parts per million (ppm) for the first time in recorded history, according to data from the Mauna Loa Observatory in Hawaii.

Since 1958, the Mauna Loa Observatory has been gathering data on how much carbon dioxide is in the atmosphere. Carbon dioxide has increased by about 24 percent since the beginning of this record. (Source: NOAA)

We rounded up a few scientists here at NASA and asked them what passing 400 ppm means to them.