Abstract: A refrigeration system including a primary stage and a secondary stage, the primary and secondary stages being thermally coupled to one another via a first heat exchanger. The primary stage including a closed-loop CO2 refrigeration system having a primary evaporator located in a region to be cooled, a primary compressor and a water-cooled primary condenser that forms at least a part of the first heat exchanger and being water-cooled by the secondary stage. The secondary stage including a closed-loop water-based cooling system having the first heat exchanger, a pump adapted to pump cooling water around the secondary stage, and a heat sink. Temperature at the (final) heat sink of the system does not need to be maintained below the supercritical temperature of the refrigerant, thus the primary (CO2) stage is operated below its supercritical temperature-pressure regime at relatively high ambient temperatures.