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How can a tiny trace gas change the climate?

"How can a minuscule amount of CO2 cause global warming?" shout the sceptics! "Easily", is the response. Can't a bite from a tiny insect produce death from a serious disease; and an injection with a tiny amount of serum reverse it?

Bite Notes: The concentration of CO2 in the atmophere is currently around 390 parts per million—just 0.004%. Ridiculing the claim that this miniscule amount can produce catastrophic climate change is common amongst sceptics.   However this ridicule is just based on intuition, not scientific evidence.Some have termed this "argument from inconceivability" —if I can't imagine it, then it must be false.   But it turns out that our intuition, which is so useful for judging human relations and things about our size, is not much help in ascertaining geophysical and astrophysical phenomena, especially things far far larger or far far smaller than we are.   As one climate science blogger writes,

I personally find it hard to believe that we are hurtling through space at 67,000 miles per hour on a big spinning rock.   It doesn't feel like it. 

In complex systems, tiny amounts of reactive substances, such as mercury, can have dramatic effects.  The generally accepted safe limit for lead in soil—around 300 ppm—is even smaller than the concentration of CO2 in the atmophere.

More examples:   

  • "Your children can drink that water, it only contains a trace of arsenic (0.01 ppm is the WHO and US EPA limit)."  This and more at
  • 800 ppm of alcohol in your blood is enough land you, handcuffed, in the backseat of a squad car.
  • About 200ppm of Potassium in the blood stream is about normal. 400ppm is fatal.
    (Patient: "Doctor, my heart arrhythmia, bradycardia and ventricular fibrillation can't possibly be due to a trace electrolyte.") [Thanks to DonaldB]
  • Perhaps the all time winner(?): one millionth of one ppm—vastly less than the CO2 concentration in the air—of botulinum toxin in your body is more than enough to kill you!

For more examples, see comments below and a closely-related bite "CO2 is only a trace gas. And arsenic is only a trace element."

Bite Source: John Russell

3 votes

Bite Details

Submitted by
John Russell
Com (2)
bysteve mann

February 29, 2012

I would also add that another substance in the atmosphere (lower stratosphere), ozone, which averages about 3 molecules of ozone to about 10 million molecules of air, absorbs 97 to 99 percent of ultraviolet radiation. If it were not for this infinitesimally small amount of ozone, there would be no life on our planet. Both ozone and carbon dioxide absorb radiation spectra at very small concentrations, ozone even much smaller than carbon dioxide. If this fact were added, I would give this an excellent rating!
bysteve mann

February 29, 2012

1 of 1 people found this review helpful
It might also be helpful to mention that over 99% of the air in the atmosphere (oxygen, nitrogen, argon) has no ability to absorb infrared radiation. When this is kept in mind, the small concentration of CO2 doesn't seem as small anymore.

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