CO2 Reaches Symbolic 400ppm Threshold

Monday 15th Jun 2015 by theWeather Club

Image: Indirect (proxy) measurements (Data source: Reconstruction from ice cores. Credit: NOAA)

In tWC newsletter issue 8 we reported that greenhouse gas emissions reached a new record high in 2013 as carbon dioxide (CO2) levels in the atmosphere reached 396 parts per million (ppm), and that at the current rate of increase, the global annual average CO2 concentration was set to cross the symbolic 400 parts per million threshold in 2015 or 2016. In May 2015 that symbolic threshold was indeed reached and for the first time in recorded history, according to data from the Mauna Loa Observatory in Hawaii. The last time CO2 was regularly above 400 ppm was three to five million years ago, before modern humans existed.

CO2 is an important greenhouse gas, which is released through human activities such as burning fossil fuels and deforestation, as well as natural processes such as respiration and volcanic eruptions. 

Since 1958, the Mauna Loa Observatory has been gathering data on how much CO2 is present in the atmosphere, with measurements indicating that CO2 has increased by around 24% since the beginning of this record.

Dr. Annmarie Eldering, NASA Deputy Project Scientist on the Orbiting Carbon Observatory-2 satellite mission said, “Reaching 400 ppm is a stark reminder that the world is still not on a track to limit CO2 emissions and therefore climate impacts. Passing this mark should motivate us to advocate for focused efforts to reduce emissions across the globe.”

In December this year, leaders from all nations of the world will meet in Paris for the UN Climate Change Conference with the objective to achieve a legally binding and universal agreement on climate.