The Mauna Loa atmospheric observatory reports the average concentration of CO₂ in the air for each month since March 1958. In the early days of this record (almost 70 years ago) it was about 315 ppm (parts per million), now we’re up to about 425.

Lest you think that anything measured in “parts per million” can only exist in very small quantity, consider that Earth’s atmosphere is gigantic — so big that if even one out of a million air molecules is CO₂, that weighs nearly 8 billion tonnes.

I’m interested in how rapidly CO₂ in the air is increasing, so I took the value for each December and subtracted the value for the previous December, in order to estimate how much CO₂ increased during that year:

In the early 1960s we burned enough fossil fuel to raise the air’s concentration by about ¾ of a ppm each year. I think of that as spending the 1960s smoking ¾ of a pack of cigarettes a day. If you’re familiar with the British Doctors Study, you know it showed without a doubt that smoking that much (15 or more cigarettes per day) increases rates of lung cancer and emphysema.

But the rate of CO₂ increase didn’t stay at ¾ of a ppm each year. It varies, a lot, from year to year, and it has also followed an upward trend. As a result, last year it rose by slightly over 3.5 ppm.

That’s like smoking three and a half packs of cigarettes a day. The new head of the EPA wants us to believe that this will be good for us.

Last year’s increase was probably higher than the trend value; after all, it was an el Nino year and they tend to show extra-high CO₂ values. But the upward trend is obvious (and yes, it’s statistically significant); not since 1992 have we seen very low values. Fun fact: the extra-low CO₂ rise in 1992 is usually attributed to the economic slowdown following the breakup of the former Soviet Union.

Fitting a trend line indicates the present rate of increase is 2.6 ppm per year (and rising). If we keep going the way we’ve been going, we’ll hit 450 in about 10 years, and cross 500 shortly after 2050 …

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