It has been argued that expenditure needed for applying a circular economy tends to be high (Kirchher et al., 2017). However, their claim is easy to counter given the many economic benefits offered by a circular economy.
This writer has used their as a substitute for a source – Kircher et al. However, since the source is in brackets and has not yet appeared in the body of the text, we have to assume that the reader has not yet seen it! Only use a pronoun as a substitute if the noun you are substituting has already been mentioned in the body of the text: Continue reading