What process limits the trapping efficiency of GHGs on Mars compared to Earth?

Answer

The extremely thin atmospheric pressure

Although Mars has significant $ ext{CO}_2$, its extremely thin atmosphere (0.0063 atm) limits trapping efficiency, a concept related to pressure broadening, whereas Venus's high pressure allows for broad absorption.

What process limits the trapping efficiency of GHGs on Mars compared to Earth?
Earthclimateatmospheregreenhouse effectwarming