Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.


Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Support

Bluesky Facebook LinkedIn Mastodon MeWe

Twitter YouTube RSS Posts RSS Comments Email Subscribe

Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...

New? Register here
Forgot your password?

Latest Posts


At a glance - How substances in trace amounts can cause large effects

Posted on 22 August 2023 by John Mason, BaerbelW

On February 14, 2023 we announced our Rebuttal Update Project. This included an ask for feedback about the added "At a glance" section in the updated basic rebuttal versions. This weekly blog post series highlights this new section of one of the updated basic rebuttal versions and serves as a "bump" for our ask. This week features "How substances in trace amounts can cause large effects". More will follow in the upcoming weeks. Please follow the Further Reading link at the bottom to read the full rebuttal and to join the discussion in the comment thread there.

At a glance

When the first edition of this rebuttal was posted in August 2011, atmospheric CO2 was at around 390 parts per million (ppm). Now (August 2023) the number is 421 ppm - and rising. 

To a non-chemist, 421 ppm might sound like a vanishingly small amount, simply because you're comparing a small number (421) with a very big one (1,000,000). It therefore comes as no surprise to find that this apparent contrast was seized upon by practitioners of misinformation. Claiming that things occuring in apparently tiny amounts must be harmless is such an easy talking-point to bandy about, since much of the intended audience is unlikely to deal with such numbers on an everyday basis. But it's also one great big red herring. Why? 

Hundreds of parts per million may not sound like a lot, but in fact many substances have important properties when present at such levels. Here are a few examples:

  • He wasn't driving drunk, he just had a trace of blood alcohol; 800 ppm (0.08%) is the limit in all 50 US states and limits are even lower in most other countries.
  • Don't worry about your iron deficiency, iron is only 4.4 ppm of your body's atoms.
  • That ibuprofen pill can't do you any good; it's only 3 ppm of your body weight (200 mg in 60 kg person).
  • The Earth is only 3 ppm of the mass of the solar system.
  • Your children can drink that water, it only contains a trace of arsenic (0.01 ppm is the WHO and US EPA limit).
  • Ozone is only a trace gas: 0.1 ppm is the exposure limit established by the US National Institute for Occupational Safety and Health. The World Health Organization (WHO) recommends an ozone limit of 0.051 ppm.

  • A few parts per million of ink can turn a bucket of water blue. The color is caused by the absorption of the yellow/red colors from sunlight, leaving the blue. Twice as much ink causes a much stronger color, even though the total amount is still only a trace relative to the water.

  • Only 500 ppm of hydrogen sulphide (bad egg gas) in air is a hazardous level, as any health and safety fact-sheet will tell you. It will make you seriously unwell at that kind of concentration. In fact, at above 100 ppm, you can no longer smell the gas because its toxicity has switched off your sense of smell. 

Just a trace-gas? Yeah, right.

It's not the concentration of a substance that necessarily matters. Instead, it's what any substance can do at a certain concentration and that property will of course vary from one substance to another. These are all useful things to recall when someone dismissively tells you that carbon dioxide is “only a trace gas”. It doesn't matter.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above

Click for Further details

In case you'd like to explore more of our recently updated rebuttals, here are the links to all of them:

Myths with link to rebuttal Short URLs
Ice age predicted in the 1970s
It hasn't warmed since 1998
Antarctica is gaining ice
CRU emails suggest conspiracy
What evidence is there for the hockey stick
CO2 lags temperature
Climate's changed before
It's the sun
Temperature records are unreliable
The greenhouse effect and the 2nd law of thermodynamics
We're heading into an ice age
Positives and negatives of global warming
Global cooling - Is global warming still happening?
How reliable are climate models?
Can animals and plants adapt to global warming?
What's the link between cosmic rays and climate change?
Is Al Gore's An Inconvenient Truth accurate?
Are glaciers growing or retreating?
Ocean acidification: global warming's evil twin
The human fingerprint in global warming
Empirical evidence that humans are causing global warming
How do we know more CO2 is causing warming?
Explaining how the water vapor greenhouse effect works
The tricks employed by the flawed OISM Petition Project to cast doubt on the scientific consensus on climate change
Is extreme weather caused by global warming?
How substances in trace amounts can cause large effects

0 0

Printable Version  |  Link to this page


Comments 1 to 2:

  1. Say I'm on the soccer field.  The ball is infrared radiation.  Against me are 50 of the best players in the World.  Can I make a goal?  Did I mention their shoes are tied together?

    Now, put one more opposing player, from the local high school, only his shoes aren't tied together.  Can I make a goal?  Suddenly, it's not as certain.  The opposing team has only grown by 2%, but my chances of making a goal have dropped around 50%.

    0 0
  2. ubrew12:

    Your analogy is a bit hard to follow. I presume that the point you are trying to make is:

    • The best players in the world will not be very effective in stopping you from reaching the goal when their shoes are tied together. As a result, your chances of scoring are high. This is analogous to IR radiation easily passing through gases that do not absorb well.
    • Even a mediocre player that is free to run around and get in your way has a good chance of stopping you, even if he only represents 2% of the players on the field (most of whom are limited by having their shoes tied together). This is analogous to CO2 blocking IR radiation, even though its concentration is  small compared to the gases that are not blocking IR radiation.
    • So, your chances of scoring are largely the result of the one player free to run around and defend against you, not the 50 players with their shoes tied. Expressing the concentration of untied players relative to the tied players is misleading.

    To extend the analogy, if they took away 25 of the players with their shoes tied, the local high school player would now be 4% of the total opposition. But that does not mean that he would be twice as effective at stopping you. He's still only one player.

    For a further look at how concentrations of CO2 in ppm can be misleading, it is worth reading this blog post (to beat my own drum):

    The Beer-Lambert Law and CO2 Concentrations

    1 0

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.

The Consensus Project Website


(free to republish)

© Copyright 2024 John Cook
Home | Translations | About Us | Privacy | Contact Us