For the first time in human history, the concentration of carbon dioxide in the atmosphere has reached 400 parts per million (ppm). The arrival at this threshold represents a powerful symbol of the growing human influence on the Earth’s climate.
“[The] increase is not a surprise to scientists,” said NOAA senior scientist Pieter Tans. “The evidence is conclusive that the strong growth of global CO2 emissions from the burning of coal, oil, and natural gas is driving the acceleration.”
Global CO2 emissions soared to a record high of 35.6 billion tonnes in 2012, up 2.6 percent from 2011 according to Climate Central’s Andrew Freedman.
The rising concentrations of carbon dioxide, in response to these emissions, have been monitored at Mauna Loa Observatory in Hawaii since 1958. They have been plotted on the iconic Keeling Curve, named after scientist Charles David Keeling, who initiated the measurements. At that time, the CO2 concentration was just 316 ppm.
It’s possible the current CO2 levels haven’t been matched in millions of years. Scripps Institution of Oceanography estimates the last time the concentration was at least 400 ppm occurred 5 to 3 million years ago, during the Pliocene Epoch.
Carbon dioxide is a heat trapping greenhouse gas and its inexorable rise in recent history coupled with an increase in the Earth’s temperature raise concerns about human interference with the climate system and where temperatures and sea levels may be headed.
During the Pliocene Epoch, temperatures were 5-7 degrees F warmer than today and sea levels were many feet higher, Scripps says.
“There’s no guarantee that we’d experience the same levels of warming in the future if CO2 levels stay that high, but it doesn’t look good,” writes Time magazine’s Bryan Walsh. “Nor will CO2 levels stop at 400 ppm—barring a virtually impossible immediate turn away from fossil fuels, CO2 emissions will keep growing globally, and CO2 concentrations will keep rising.”
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Here’s a nice infographic from Climate Central
See also, this well-done Climate Central piece: The Last Time CO2 Was This High, Humans Didn’t Exist