(Image source: Keeling Curve)
In May of 2011, worldwide CO2 levels hit a yearly maximum of 394 parts per million. At the most recent average rate of CO2 increase (about 2 parts per million each year), the world would have hit 400 parts per million by 2014. Instead, that number was reached 1 year sooner.
It was a faster rate of atmospheric carbon increase — about 3 parts per million rise each year — that resulted in the world rocketing to the new milestone sooner than expected.
Pace of Rise Accelerating
The pace of atmospheric CO2 increase, at the time measurements began in the late 1950s, was about 1 part per million each year. This pace of increase steadily rose to an average of 2 parts per million each year during the late 1990s. By the end of the first decade of the 21rst Century, average rates of increase were about 2.2 parts per million.
This accelerating pace of CO2 accumulation has been driven, largely, by a vast increase in the amount of CO2 released into the atmosphere. In the late 1950s, the world dumped about 8 gigatons of CO2 into the atmosphere each year. By 2012, that number had nearly quadrupled to 31.6 gigatons.
But Carbon Sinks Keep Pace with Rising Emissions
You’ll notice that though carbon emissions nearly quadrupled, the average pace of atmospheric carbon increases only slightly more than doubled. The reason for this is that as global emissions rose, the amount of carbon absorbed by the oceans and the land also dramatically increased. So both the oceans and land together continued to absorb about 50% of all the carbon our factories and automobiles spat out.
The remaining fraction still ended up in the atmosphere. And so we still saw a rapid increase in global CO2 levels. But not so rapid as we would have if carbon sinks weren’t helping us by drawing down half of the CO2 we were dumping.
(Image source: NOAA)
…Until They Become Exhausted
Unfortunately, carbon sinks are a finite resource. As such, scientists expect them to eventually lag in their ability to uptake ever greater volumes of our greenhouse gas emissions. This is especially true with the oceans which a number of scientific reports show are starting to reach their saturation point.
According to a recent NOAA report:
“The uptake of carbon dioxide by the oceans and by ecosystems is expected to slow down gradually,” Tans [one of the report's authors] said. Oceans, for example, are already becoming more acidic as they absorb about a quarter of the carbon dioxide pumped into the air by human activities. “As the oceans acidify, we know it becomes harder to stuff even more CO2 into the oceans,” Tans said. “We just don’t see a letup, globally, yet.”
In fact, a related research paper found that a large swath of the southern ocean, which absorbs 15% of the world’s CO2 emissions, had become completely saturated and could no longer absorb CO2 from the atmosphere.
A New, Very Dangerous Pace of Increase Going Forward?
So all this begs the question: are the world’s CO2 sinks starting to become exhausted?
A six parts per million CO2 increase over two years is a much more rapid rate than the world is used to. At such a rate, we reach 450 parts per million by 2030. And if the world’s carbon sinks are, indeed, starting to exhaust even as world CO2 emissions remain high or continue to climb, then we may see annual increases of 4 parts per million or more over the coming decades.
We won’t know if the 3 parts per million annual increase is established for a few years yet. But if it is, it is yet one more sign that the world is starting to reach a number of very dangerous tipping points and we should do our best to reduce the potential harm by as much as possible.