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Climate hits 400ppm of CO2 for first time in 3 million years

It is a sign of our rapidly changing world that we can get daily updates on the rising levels of carbon dioxide in the atmosphere via Twitter. @Keeling_Curve is the Twitter account of the Scripps Institution of Oceanography and tweets daily readings from the Mauna Loa Observatory in Hawaii, which has been measuring how much carbon dioxide is in the air since 1958. In what is a symbolically significant milestone, on May 9th NOAA reported CO2 levels of 400.03 parts per million (ppm), which is a level unseen for three million years.

This milestone is, undoubtably, bad news. However, the newsworthiness of this moment also serves as an opportunity to educate the public about what this number means for the climate and our future.

What does this number, 400 ppm, mean?

A post at the Scripps Institution of Oceanography puts the milestone in historic context:

Prior to the Industrial Revolution, natural climate variations caused atmospheric CO2 to vary between about 200 ppm during ice ages and 300 ppm during the warmer periods between ice ages. At the dawn of the Industrial Revolution, around the year 1780, the CO2 concentration was about 280 ppm, so CO2 had already risen by around 40 ppm before Keeling began his measurements. Anyone who has breathed air with less than 300 ppm CO2 is now over 100 years old!

UC San Diego/via

What does 400 ppm look like?

Robert Monroe explains what a world with 400 ppm CO2 looks like:

Recent estimates suggest CO2 levels reached as much as 415 parts per million (ppm) during the Pliocene. With that came global average temperatures that eventually reached 3 or 4 degrees C (5.4-7.2 degrees F) higher than today’s and as much as 10 degrees C (18 degrees F) warmer at the poles. Sea level ranged between five and 40 meters (16 to 131 feet) higher than today.

In his great talk on why climate change is simple, David Roberts explained what scientists predict the world will look like at various levels of warming. With warming of 2º Celsius now appearing to be all but inevitable, Roberts focused on what we can expect with warming of 4º C.

Justin Gillis at The New York Times puts the warming in perspective:

For the entire period of human civilization, roughly 8,000 years, the carbon dioxide level was relatively stable near that upper bound. But the burning of fossil fuels has caused a 41 percent increase in the heat-trapping gas since the Industrial Revolution, a mere geological instant, and scientists say the climate is beginning to react, though they expect far larger changes in the future.


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