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Have atmospheric carbon levels passed the point of no return at 400ppm?

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By some definitions, yes.

Recently a number of articles have claimed that the atmospheric carbon levels have passed the "point of no return", at 400 parts per million. However, the choice of the 400ppm milestone may be somewhat arbitrary.

Origin and Prevalence

In 2013, NASA scientists already reacted to what they called the 400 parts per million (ppm) carbon milestone. For the first time in recorded history the Mauna Loa Observatory in Hawaii found the levels hitting 400 ppm. The Mauna Loa Observatory, located in Hawaii, measures highly accurate measurements of atmospheric carbon. On November 11, 2015, it was recorded that 399.68 parts per million (ppm) of the molecules in the atmosphere were carbon dioxide. The next day, it measured at 401.64 ppm. Ever since that day, the amount of carbon dioxide in the atmosphere has stayed above 400 ppm.

The first found evidence of this claim is a 2013 article, "NASA scientists react to 400ppm carbon milestone."

The first claim was made in May, 2016 by a NCAR scientist named Britton Stephens, co-lead principal investigator for ORCAS. He claimed that "This is the last we'll see of sub-400 ppm CO2 in the Southern Hemisphere, unless we're able to some day achieve negative emissions,"

An article published May 6, 2015 by National Oceanic and Atmospheric Administration (NOAA) reaffirms the claim and it was reported that all Arctic sites had reached 400ppm in the Spring of 2012 and in 2013, NOAA record had reached 400ppm. NOAA data also shows the average growth rate of carbon dioxide during the years from 2012 to 2014 was 2.5ppm, which was the "highest recorded ever over three consecutive years." [source]

A 2015 article from Scientific American labels 450 ppm as the dreaded point of no return, where cascading effects kick in. A 2016 NCAR Report notes a 400ppm milestone is important due to the earth's condition last time such a level was reached.

"It was only a matter of time that we would average 400 parts per million globally," said Peter Tans, lead scientist of National Oceanic and Atmospheric Administration's Global Greenhouse Gas Reference Network.


Issues and Analysis

Carbon and oxygen are naturally occurring gasses all over the world and when they bond, they form carbon dioxide. Carbon dioxide is a greenhouse gas, which are gasses that trap heat in the atmosphere and contribute to climate change. Carbon dioxide makes up over 50% of the greenhouse gasses because humans produce carbon dioxide by burning coal or oil, cutting down trees or destroying other vegetation, or by the production of certain chemicals. By burning fossil fuels, people are adding carbon, in the form of carbon dioxide, faster than natural activity can remove it.

The article from Complex asserts that we are past the point of no return; however, other articles seem to suggest that there is still the possibility for the carbon levels to fall below 400 ppm. The article's title makes a partially true claim: carbon levels are through the roof, but as of yet we can't be sure if we are in fact past the point of no return. Scientists have agreed that the CO2 levels only seem to be rising and that it is highly unlikely for us to see them drop below 400 ppm this year, but there is a possibility that they might drop next year or the year after that. Additionally, there is still emerging evidence needed to explore this issue further because the subject is under continuous research and keeps evolving. Other people predict that we might not see another day below 400 PPM if we don't change the way we pollute the earth. Co2 levels have been rising each year and have been increasing at the fastest we have ever seen them.

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