No specific rules exist to quantify the carbon impact of taking out a loan. Generally speaking, no GHG emissions are accounted for when a company gets a loan.
Nevertheless, a distinction can be made between principal and interest payments
Principal payments: no carbon impact as the money is used to purchase products or services, invest, etc. Otherwise, emissions resulting from the loan would be double counted.
Interest payments: this amount can be linked to GHG emissions. To estimate these emissions, the monetary emission factor bank fees and services is used (0,13 kgCO2e/GBP or 0,078 kgCO2e/USD)