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CO2 on Path to Cross 400 ppm Threshold for a Month

Last year, atmospheric carbon dioxide briefly crossed 400 parts per million for the first time in human history. However, it didn’t cross that threshold until mid-May. This year’s first 400 ppm reading came a full two months earlier this past week and the seeming inexorable upward march is likely to race past another milestone next month.

“We’re already seeing values over 400. Probably we’ll see values dwelling over 400 in April and May. It’s just a matter of time before it stays over 400 forever,” said Ralph Keeling in a blog post.

Keeling runs a carbon dioxide monitoring program for Scripps Institute of Oceanography, a position he took over from his father who started it. The program takes daily measurements from the Mauna Loa Observatory in Hawaii, which sits at 11,141 feet on a volcano’s northern flank. Measurements have been recorded there continuously since March 1958. They’ve risen steadily since the first measurement of 313 ppm as humans have continued to burn more fossil fuels.

The Keeling Curve, which shows monthly carbon dioxide concentrations at Mauna Loa Observatory.
Credit: NOAA Earth System Research Laboratory/Scripps Institute of Oceanography

The graph of those concentrations is known as the Keeling Curve, one of the most iconic images in science. In addition to showing a steady rise in carbon dioxide, the graph also shows the seasonal variations in the curve. In Northern Hemisphere spring, plants burst to life and suck carbon dioxide out of the air until they die off in the fall.

Atmospheric carbon dioxide usually peaks in May. If levels continue to rise in the next few months — and there’s no reason to believe they won’t — April or May will likely be the first time the monthly atmospheric carbon dioxide average will be above 400 ppm. Estimates for when the atmosphere last contained this much carbon dioxide range from 800,000 years ago all the way to 15 million years.

While 400 ppm is mostly a symbolic number, the climate changes it could cause are not. Among other impacts, increased carbon dioxide contributes to heating the planet’s surface and ocean temperatures, which in turn melts ice and raises ocean levels.

Oceans have already risen 8 inches in the past century and may rise another 3 feet by the end of the century with grave costs to coastal communities. When carbon dioxide was last at these levels, polar ice melted and flooded the oceans, raising levels up to 130 feet higher than today's levels.

Temperatures were also up to 11°F above today’s temperatures. In the next century, temperatures are projected to increase by up to 8.6°F if emissions aren’t reduced.

The big difference between the current carbon dioxide levels and the last time they were this high is how fast they’ve increased in recent times. That rate shows little sign of slowing.

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By john harkness
on March 18th, 2014

Oh, and if we’re already around 400 now and May is usually the peak, aren’t we likely to see many more than just _one_ month of above 400 readings? Even Keeling’s quote shows he thinks it will be at least two.

Heading into an El Nino year, shouldn’t we expect even higher values, since a warmer ocean surface will not absorb as much CO2 (and will probably release some) as in neutral or La Nina years?

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By john harkness
on March 18th, 2014

It looks like the current official numbers for the last 7 days average over 400 now!

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By Dave (Basking Ridge, NJ 07920)
on March 18th, 2014

Scripps also track the decline in atmospheric oxygen concentration, which is considered to be due to the consumption of oxygen when fossil fuels are consumed.

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By R. L. Hails Sr. P. E. (Ret.) (Olney/MD/20832)
on March 19th, 2014

This is a problem.

There is no known or realistically expected energy source, other than carbon combustion, which can sustain 7+billion people.  (Uranium can contribute in advanced societies.)  Some futurists have estimated a asymptotic sustainable global population at a few million, give or take.  Thus, if these AGW predictions are any where near correct, the world must experience a die off of humans at a death rate many times greater than at the height of World War II, but continuing unabated over the next century.

How this is peaceably resolved is beyond me.  I go to church.

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By john harkness
on March 21st, 2014

Hails, I notice that you don’t support your claim. That doesn’t mean it isn’t true, just that it may be based on some dubious assumptions.

One such assumption may be that industrial ag currently supports the current population. But let’s look at the largest industrial crop in the US—corn. Less than a tenth of the US corn crop goes directly to feeding people. The rest mostly feeds cars, cows, and industry. So the entire industrial ag corn crop could go away tomorrow and most people would see no increase in their food bill or reduction of their ability to feed themselves. (That US corn alone, by the way, could provide everyone in the world with over the 2000 calories per day needed to survive and be active.)

If we stopped feeding corn to cars and cows, stopped eating the same corn-fed cows and ate the grain directly, mostly stopped driving and (especially) flying…and distributed what’s left more equitably, probably the current population could be just barely sustained.

Not to say that population growth isn’t an enormous problem. Just that it’s not the only part of the equation. Remember that the top 20% of us consume about 80% of all the resources.

We have to do what we can to encourage women’s rights around the world, since this has been most clearly correlated with reduced birth rates. If we could rapidly accelerate the current trend of women having only one child and that only after their late twenties or later, we could conceivably still allow ‘natural’ death rates to do the depopulation you mention without the brutality you envision.

But praying is still a good idea.

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By Chuck Greene (Ithaca NY 14850)
on March 22nd, 2014

Just went to Mauna Loa Observatory on Wednesday, and carbon dioxide concentration was 400.6 ppm. Direct air capture will be the only way to avoid dangerous climate change. Reducing emissions as much as possible is critical but not sufficient by itself.

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By Josef Biesenberger (Germany)
on March 23rd, 2014

CO2 increase back on growth-track;
view graphs with latest data:

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