The concentration of carbon dioxide in the earth's upper atmosphere has again reached record highs.
The atmospheric observatory at Hawaii's Mauna Loa last week recorded a concentration of 415 parts per million, a new high.
In 2013, concentrations exceeded 400 parts per million for the first time.
The Mauna Loa observatory began recording carbon dioxide levels over 60 years ago, when concentrations were fewer than 315 parts per million.
The US National Oceanic and Atmospheric Administration said three of the four highest annual increases have occurred in the past four years.