The concentration of carbon dioxide in the atmosphere has passed the 400 ppm threshold. This has not happened for millions of years.
It looks like the Earth has crossed a landmark threshold amid global warming.
Typically, in September, the levels of carbon dioxide (CO2) in the atmosphere are minimal. This concentration is the benchmark against which fluctuations in greenhouse gas levels are measured throughout the next year. But in September of this year, CO2 levels remain high, at about 400 ppm, and many scientists believe that the concentration of greenhouse gases will not fall below this threshold during our lifetime.
The Earth has consistently accumulated CO2 in the atmosphere since the Industrial Revolution, but the 400 ppm level creates a new rate that has not been seen on our planet for millions of years.
“The last time CO2 in the atmosphere of our planet was 400 ppm was about three and a half million years ago, and the climate was very different from today,” an associate professor at the School of Marine and Atmospheric Research told Christian Science Monitor by email. Phenomena at State University of New York at Stony Brook David Black.
“In particular, in the Arctic (north of 60th latitude) it was much warmer than today, and the sea level on the planet was 5-27 meters higher than the current one,” Black said.
“Then the atmosphere took millions of years for the CO2 level in it to reach 400 ppm. And it took millions of years more for it to fall to 280 ppm (the figure was on the eve of the industrial revolution). Climatologists are very concerned that people in just a few centuries have done what nature has done in millions of years, with most of these changes occurring in the last 50-60 years.
The global CO2 concentration has been periodically rising above 400 ppm for several years; however, during the summer growing season, a significant part of the carbon dioxide in the atmosphere is absorbed in the process of photosynthesis, and therefore the CO2 level is below this mark for most of the year.
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But due to human activities (primarily due to the combustion of fossil fuels), more CO2 is emitted into the atmosphere, and the annual minimum was getting closer and closer to the 400 ppm mark. Scientists fear that the planet has reached a point of no return this year.
“Is it possible that in October 2016 the monthly indicator was below September, dropping below 400 ppm? Practically not,”wrote the director of the program at the Institute of Oceanography. Scrips Ralph Keeling.
There have been cases in the past when CO2 levels have dropped below their previous September values, but these are extremely rare. According to scientists, even if the world completely stops emitting carbon dioxide into the atmosphere from tomorrow, its concentration will remain above 400 ppm for several years.
“In the best case (in this scenario), stabilization can be expected in the near future, and therefore the CO2 level is unlikely to change much. But in 10 years or so, it will begin to decline,”NASA chief climatologist Gavin Schmidt told Climate Central. "In my opinion, we will no longer see a monthly rate below 400 ppm."
While the rise in CO2 concentration in the atmosphere gives cause for concern, it should be noted that the 400 ppm mark itself is more of a route reference than a hard indicator that heralds a climate apocalypse for the world.
“People love rounded numbers,” says Damon Matthews, an environmental professor at Concordia University in Montreal. "It is also very symbolic that, in parallel with the increase in CO2, the global temperature has exceeded the pre-industrial level by one degree."
Of course, these indicators are mostly symbolic, but they are a real illustration of the trajectory that the earth's climate is following.
“CO2 concentration is somewhat reversible because plants absorb carbon dioxide,” says Dr. Matthews. "But the temperature arising on the basis of such changes is irreversible in the absence of human effort."
Carbon dioxide in the form of a greenhouse gas not only contributes to global warming, but also negatively affects the state of the world's oceans due to acidification. When carbon dioxide dissolves in large volumes in water, some of it is converted to carbon dioxide, which reacts with water molecules to produce hydrogen ions, which increases the acidity of the ocean environment. This in turn leads to coral bleaching and interferes with the life cycle of small organisms, which also negatively affects larger organisms further down the food chain.
The 400 ppm threshold news comes as world leaders have taken several steps to ratify the Paris Agreement on Climate Change, which aims to systematically reduce carbon emissions around the world, starting in 2020.
The countries ratifying the agreement have a lot of work to do.
“To reduce atmospheric CO2 levels on a time scale of several centuries, we need to not only use and develop non-carbon energy sources; we also need to remove CO2 from the atmosphere by physical, chemical and biological methods, says Black. “There is a technology for removing atmospheric CO2, but in the scale of the existing problem it is not yet applicable.”