#CO2 #Earth – Earth CO2 levels: Have we crossed a point of no return? : Earth may have passed a significant symbolic threshold as the global climate continues to grow warmer. Usually, September marks a low in the amount of carbon dioxide (CO2) in the atmosphere. This concentration sets the bar over which levels of the greenhouse gas will fluctuate throughout the next year.
But this September, CO2 levels are staying high, at around 400 parts per million, and many scientists think that we will not see levels of the greenhouse gas drop below that threshold within our lifetimes.
Earth has been steadily building up CO2 in the atmosphere since the Industrial Revolution, but the 400 ppm landmark is creating a new normal that hasn’t been seen on this planet for millions of years.
“The last time our planet saw 400 ppm carbon dioxide in our atmosphere was about 3.5 million years ago, and global climate was distinctly different than today,” David Black, associate professor in the School of Marine and Atmospheric Sciences at Stony Brook University in New York, tells The Christian Science Monitor in an email.
“In particular, the Arctic (north of 60°) was substantially warmer than present, and global sea level was anywhere between 15 and 90 feet higher than today,” Professor Black says.
“It took millions of years for the atmosphere to reach 400 ppm CO2 back then, and it took millions of years for the atmospheric CO2 to drop to 280 ppm right before the industrial revolution.
One of the things that really concerns climate scientists is we as humans have taken only a few centuries to do what nature took millions of years, and most of that change was just in the last 50-60 years.”
While global concentrations have spiked above the 400 ppm level for several years, the summer growing season has always absorbed enough atmospheric CO2 through photosynthesis to keep concentrations below that mark for the bulk of the year.
As human activities – mainly the burning of fossil fuels – have flooded more CO2 into the atmosphere, however, the annual low point has inched closer and closer to that 400 ppm mark. This year, scientists fear that the planet may have reached a point of no return.
“Is it possible that October 2016 will yield a lower monthly value than September and dip below 400 ppm? Almost impossible,” wrote Ralph Keeling, director of the program at Scripps Institution of Oceanography, in a blog post last week.