A method of producing liquefied natural gas using liquid nitrogen as a primary refrigerant, the method comprising: providing a natural gas stream from a supply of natural gas; providing a liquefied nitrogen stream from a supply of liquefied nitrogen; passing the natural gas stream and the liquefied nitrogen stream through a first heat exchanger that exchanges heat between the liquefied nitrogen stream and the natural gas stream to at least partially vaporize the liquefied nitrogen stream and at least partially condense the natural gas stream; characterised in that the method comprises removing greenhouse gas from the at least partially vaporized nitrogen stream using a greenhouse gas removal unit that comprises a distillation column and a heat pump condenser and reboiler system; increasing a pressure and condensing temperature of an overhead stream of the distillation column; cross-exchanging the overhead stream of the distillation column and a bottoms stream of the distillation column to affect both an overhead condenser duty and a bottom reboiler duty of the distillation column; reducing a pressure of the distillation column overhead stream after the cross-exchanging step to produce a reduced-pressure distillation column overhead stream; separating the reduced-pressure distillation column overhead stream to produce a first separator overhead stream, wherein the first separator overhead stream is gaseous nitrogen that exits the greenhouse gas removal unit having greenhouse gases removed therefrom; and providing an additional heat exchanger in which the first separator overhead stream exchanges heat with the natural gas stream to increase a temperature of the first separator overhead stream to at least ambient temperature prior to the first separator overhead stream being vented to atmosphere. providing a natural gas stream from a supply of natural gas; providing a liquefied nitrogen stream from a supply of liquefied nitrogen; passing the natural gas stream and the liquefied nitrogen stream through a first heat exchanger that exchanges heat between the liquefied nitrogen stream and the natural gas stream to at least partially vaporize the liquefied nitrogen stream and at least partially condense the natural gas stream; characterised in that the method comprises removing greenhouse gas from the at least partially vaporized nitrogen stream using a greenhouse gas removal unit that comprises a distillation column and a heat pump condenser and reboiler system; increasing a pressure and condensing temperature of an overhead stream of the distillation column; cross-exchanging the overhead stream of the distillation column and a bottoms stream of the distillation column to affect both an overhead condenser duty and a bottom reboiler duty of the distillation column; reducing a pressure of the distillation column overhead stream after the cross-exchanging step to produce a reduced-pressure distillation column overhead stream; separating the reduced-pressure distillation column overhead stream to produce a first separator overhead stream, wherein the first separator overhead stream is gaseous nitrogen that exits the greenhouse gas removal unit having greenhouse gases removed therefrom; and providing an additional heat exchanger in which the first separator overhead stream exchanges heat with the natural gas stream to increase a temperature of the first separator overhead stream to at least ambient temperature prior to the first separator overhead stream being vented to atmosphere.