It marked the first time in the 60-year history of the Keeling Curve, measured at Mauna Loa Observatory in Hawaii, that a monthly average exceeded that threshold.
The Keeling Curve, which draws its name from its creator, the late Charles David Keeling of the Scripps Institution of Oceanography in La Jolla, has tracked a seasonally seesawing trend of steadily rising CO2 readings.
The Keeling Curve just exceeded 400 ppm in air for the first time in human history in 2013, now topping that level again this April. That represents a 30-percent increase in carbon dioxide concentration in the global atmosphere since the Keeling Curve began being measured in 1958.
Carbon dioxide is called a greenhouse gas for its ability to trap solar radiation and keep it confined to the atmosphere. It is the most prevalent among all greenhouse gases produced by human activities, attributed to the burning of fossil fuels.
Prior to the onset of the Industrial Revolution, which began about 1760, CO2 levels had fluctuated over the millennia but had never exceeded 300 ppm at any point in the last 800,000 years.
What does this portend for Earth’s climate and mankind’s future?
Though not a “point of no return,” Ralph Keeling, Charles’ son, who is continuing his father’s research work at Scripps, noted the CO2 threshold just crossed should serve as a wake-up call for humanity.
“It’s an arbitrary point, in a way, a round number,” said Ralph Keeling, pointing out “280 was the CO2 level” that prevailed before the industrial revolution, a figure previously unchanged during the preceding 10,000 years of Earth history.
What does the additional 120 ppm increase of CO2 since 1958 in the Earth’s atmosphere indicate?
“The human impact of taking fossil fuels out and burning them, a direct forcing of the climate (warming) through human emissions,” answered Keeling. “It’s clear now that climate is going to change, one way or another. It’s just a question of how bad it’s going to be.”
Keeling and most other scientists are contending that, even if it were possible to halt all CO2 emissions immediately, that pent-up atmospheric CO2 levels would continue to rise for many years.
A partial solution, said Keeling, is to minimize CO2 emissions as much as possible by shifting to non-CO2 producing, renewable energy sources like solar, wind and geothermal, as soon and as much as possible.
Asked what the best-case scenario would be if renewable energy replaces fossil fuels, Keeling foresees “a slower rise in CO2 levels stabilizing at 470 to 490 ppm.”
The Scripps scientist said his wish is that “the Keeling Curve becomes a symbol of hope, rather than of despair.”
Is Keeling optimistic mankind’s CO2 “destiny” will be best-case rather than worst-case?
“There is every reason to think that (slowing the rise of CO2) could happen in the next decade or two,” he said.
And what happens in a worst-case scenario, where humans do nothing and rising CO2 levels continue unchecked?
Replied Keeling, “The reality for the human population could be climate refugees, people forced to move, from one place to another, because of changing climate impacting seasonal rainfall and crop-growing patterns.”
But Keeling was quick to point out, “Too much gloom and doom aren’t helpful. The world is changing all the time. Change isn’t always disastrous. Humans are good at challenges. We just have to live up to this one.”
In honor of the 60th anniversary of the Keeling Curve, there’s a video of Ralph Keeling of the Scripps CO2 Program, which shows how scientists make carbon dioxide measurements and give a guided tour of the original instruments his father, Charles David Keeling used. Visit scripps.ucsd.edu/programs/keelingcurve to view the video.