Carbon dioxide is given a GWP of 1. A refrigerant with a GWP of 1,000 would, if leaked, have roughly the same warming effect over 100 years as a thousand times its weight of CO2. Widely quoted 100-year values are about 1,430 for R134a and close to 3,900 for R404A, while hydrocarbons such as R290 and R600a are in single digits and R744 (CO2) is 1.
GWP matters because refrigerant leaks during use, servicing and scrapping. A commercial cabinet that leaks a few hundred grams of a high-GWP refrigerant has the same climate effect as a large amount of CO2. Low-GWP refrigerants remove most of that impact, even if a unit is serviced carelessly or abandoned at end of life.
Published GWP figures differ slightly depending on which assessment report is used, so you may see different numbers for the same gas. The direction is what counts for a buyer: the international HFC phase-down under the Kigali Amendment is steadily reducing the use of high-GWP refrigerants, which affects availability and service cost over a cabinet's life.