CO₂ or CO2?

In mathematics and in chemical formula, indices are to be subscripted. In the discussion on advancing climate change, the sum formula CO2 is often mistakenly used in digital media for the greenhouse gas carbon dioxide instead of the correct representation CO₂, i.e., without the subscript 2 to indicate that the molecule consists of two oxygen atoms. But there is a reasonably simple way to use the correct sum formula in word processing programs and digital media.

First, it can be debated whether it is a problem to represent the chemical formula for carbon dioxide with CO2. The general public will not notice an immediate difference in the statements of an article if CO2 is used. There is also more effort for authors, especially in digital or social media, to find a way to subscript index 2 since digital content publishing programs generally do not provide a way to subscript index 2.

From a scientific perspective, however, the use of CO2 as the chemical formula of carbon dioxide is incorrect (sometimes you even encounter the completely wrong CO²). According to the convention, the number of different atoms in a molecule is represented as an index, i.e., CO₂ for carbon dioxide or H₂O for water or CH₄ for methane. Therefore, for correct representation, care must be taken to subscript the indices accordingly. The same must be observed when the superscribing index, for example, designating the square meter m² instead of m2 or m^2 or sqm. And the same applies to mathematical equations where, for example, the multiplication is represented as the so-called circle operator ⋅ (multiplication sign) and not as * (asterisk operator) or x (cross product).

In word processing programs, the subscript or superscript of indices and numbers can be easily solved by formatting the text. Here, the character is slightly lower or higher in a slightly smaller font. The problem is that when the text section is reformatted by adjusting the font size, all characters may be displayed in the standard size again, and the subscript or superscript has been removed. In spreadsheet programs, the subscript or superscript is even more complex. However, in these programs, it is essential to use a correct representation due to units or mathematical quantities. 

The dilemma can be solved by inserting appropriate characters predefined in the fonts on computers or mobile devices. These include characters from different languages (Greek, Cyrillic, etc.), superscript and subscript characters, and mathematical operators. For the standard operating systems, the characters can be entered directly from the keyboard with a bit of effort:

The input of Unicode characters under Windows:
The input of Unicode characters under Apple macOS:

A bit more comfortable is to copy and paste the corresponding characters. The University of Regensburg, for example, has compiled a list of the most important special characters in tabular format

All superscript and subscript characters can be found at

and the mathematical operators under

A complete list of Unicode blocks can be found at

Copying the appropriate character and pasting it into the text, spreadsheet cell, or axis label in charts can ensure that the proper consistency is not lost when formatting changes or customization occurs. And the characters can also be displayed correctly on digital pages and social media. 

In handwriting, using appropriate indexes or mathematical operators is not a problem. The effort in the digital world is somewhat more significant. The danger of the ubiquitous digital content with the incorrect use of the indices or operators is that this representation is also transferred to the handwritten part and thus seems universally valid. However, in science (and thus also in the general public), the correct picture of such apparent details is elementary, since otherwise, it can lead to meaning-distorting or incorrect content. Convenience in articles or texts must therefore not take precedence over correctness. In science (this includes theses, studies, or similar reports), the correct use is consequently obligatory; in other publications, the proper presentation belongs, and a correct orthography and punctuation are expected. Science should have the same weight in formatting as linguistic correctness, even if the effort is more significant at one point or another.


Prof. Dr. Henrik te Heesen
Prof. Dr. Henrik te Heesen
Professor FB Umweltplanung/Umwelttechnik - FR Maschinenbau


+49 6782 17-1908


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