Researchers have announced that the concentration of carbon dioxide in the earth’s atmosphere is now at levels not seen for at least 2.5 million years.
We can all now claim part of the dubious honour of living in a time no other humans have ever experienced.
Carbon dioxide levels recorded at the Mauna Loa Observatory in Hawaii hit 415 parts per million (ppm) last week. This is more than 100 ppm higher than at any time in the 800,000 years of data scientists have access to on world carbon dioxide concentrations. For perspective, the last time these levels hit 300ppm, humans didn’t exist.
Scientists say while the earth has gone through periods of cooling and warming in the past, these events have taken a very long time to occur. For nearly a million years carbon dioxide levels in the atmosphere have been, on average, 280 ppm, not rising above 300 ppm or dipping below 160 ppm. In the past, global warming has happened gradually over thousand-year periods, while the latest human-caused warming event is happening over just a couple of centuries.
Johannes Feddema, professor and chair of climatology at UVic, says the rate of temperature change is alarming, but unfortunately not unexpected. He says over the 18,000 years from the Ice Age to 1900, the rate of temperature change was 0.036. During the 100-year period from 1900 to 2000, the temperature change was 0.7 - a 20-fold increase. And worryingly, Feddema says over the last 20 years, “We have almost matched that 100-year record in increase, in CO2.”
Ice cores from the Antarctic ice sheet preserve snapshots of how much greenhouse gas was in the atmosphere over hundreds of thousands of years. Readings taken from them show a dramatic increase in carbon dioxide levels at the start of the Industrial Revolution.
Over the past 10 years, the level of CO2 in the atmosphere has risen by an average of 2.5 ppm every year, hitting 400 ppm in 2013.
“It’s unprecedented, as far as human history is concerned. We’ve never seen this before,” says Feddema.
“However, from a climate science point of view this is absolutely not unexpected. What is disconcerting is that despite all the discussions we’ve had, Paris, Copenhagen, etc. [United Nations climate talks], we’re not slowing down at all and we’re on a trajectory some call business as usual, but worse. We haven’t really made any dents about doing something about this.”
So why we aren’t we seeing catastrophic effects yet? Feddema makes an analogy linking the earth, covered in oceans, to a pot of water boiling on a stove. It might take a while to get going but once it starts boiling it is difficult to stop, even after turning off the heat.
“We have a certain momentum going here that even if we manage to do everything right, things are going to continue to change for a while. And a while being in the order of a hundred years.”