Carbon dioxide levels in the atmosphere have passed 400 parts per million (ppm) for the first time in human history. Data released on Friday from two monitoring stations in Hawaii run by the U.S. National Oceanic and Atmospheric Administration and the Scripps Institution of Oceanography show that the daily average of climate-warming greenhouse gas has passed 400ppm for the first time in the 50 years that the two stations have been recording. 350ppm is widely considered to be the safe upper limit for CO2 in our atmosphere.
The revelation further underscores the importance of taking significant and concerted action to mitigate the impact humanity has on the climate and to address the effects, including rising temperatures, melting ice caps, retreating glaciers, and the more frequent extreme weather events that we are already witnessing. And the longer that things continue along their present course, the harder this will be.
The milestone comes as two recently published studies added further support to the famous hockey stick graph which shows that "the late 20th century warmth in the Northern Hemisphere was unprecedented during at least the last 1,000 years." Although CO2 levels fluctuate seasonally and we are not yet at global annual averages above 400ppm, the data is a sober warning about the human impact on the climate. The last time that there was so much CO2 in the atmosphere was "several million years ago, when the Arctic was ice-free, savannah spread across the Sahara desert, and sea level was up to 40 metres higher than today." And as global emissions continue to rise unchecked, Damian Carrington of the Guardian writes that "these conditions are expected to return in time, with devastating consequences for civilisation" unless emissions are rapidly reduced.
Image credit: Scripps Institution of Oceanography
Back before industrialisation began, the CO2 level in the atmosphere was around 280ppm (see the video below for a history of atmospheric carbon dioxide up until January 2012). Reacting to Friday's announcement, Professor Rajendra Pachauri, chair of the Intergovernmental Panel on Climate Change, called the milestone a "significant reminder of the rapid rate at which — and the extent to which — we have increased the concentration of greenhouse gases in the atmosphere." He went on to express his hope that the milestone will increase awareness of the "scientific reality of climate change and how human society should deal with the challenge."
While 400ppm might not seem significant given that CO2 levels in the atmosphere were already above 390ppm, the Guardian's George Monbiot argues that it is "symbolic of our failure to put the long-term prospects of the natural world and the people it supports above immediate self-interest." The only way forward now, he continues, "is back: to retrace our steps and seek to return atmospheric concentrations to around 350ppm." And as the 350.org campaign says, "the only way to get there is to immediately transition the global economy away from fossil fuels and into into renewable energy, energy efficiency, and sustainable farming practices in all sectors (agriculture, transport, manufacturing, etc.)"
The evidence of man-made climate change is clear. We should not be continuing to debate whether it is happening or not, instead we should be working out ways address it. At all levels of society, from individuals to governments, we can, and should, take action to begin to reverse the trend of rising greenhouse gas concentrations in the atmosphere. Now is not the time for ignorant or self-interested denialism, it is the time for action.