A freelancer I work with told me that I can replace emissions with output. Is it correct to use output when talking about carbon emissions per person? It sounds unnatural to me because how can a person outputs carbon emissions? Ngram shows that carbon output per person is not used at all.
I understand I can say a country's carbon dioxide output. But here I have "per person".
Carbon dioxide emissions/output per person in the US decreased.
Humans do emit carbon dioxide individually. They eat and oxidize carbon-containing materials (food), and they breathe out carbon dioxide.
But that is probably not what the expression "carbon dioxide emissions/output per person" means. It probably means the total carbon dioxide produced by a nation or area, divided by the the number of people living there.
In that case, either emissions or output could be used.
It could be an important number to pay attention to, since people living in primitive conditions will produce less carbon dioxide per person than those in modern industrialized countries with industries and cars.
It's rare that two words could be truly "interchangeable," in all situations. But to explain a word we have to use other words, so we often say "Word A means Word B." But sometimes some words have multiple meanings and only some of them overlap: "A paper" means pretty much the same as "a document," but "some paper" is different than "some documents." And other times, even if two words have similar meanings, we get in the habit of using one for a certain setting or in a certain phrase.
So yes, "emissions" and "output" both mean "what comes out of something." But "output" also has meanings about productivity: what I accomplish at my job is my "output," and "emissions" wouldn't fit there. Similarly, in an ecological context, "carbon emissions" is an established phrase and we can't substitute other synonyms without causing some confusion.
