Short answers, pulled from the story.
Refrigeration is an artificial method of cooling a space, substance, or system below the ambient temperature by removing heat from a low-temperature medium and rejecting it at a higher temperature. The work of that energy transfer is traditionally driven by mechanical means, but it can also be driven by heat, magnetism, electricity, or laser.
Jacob Perkins built the first working vapor-compression refrigeration system in the world in 1834. It was a closed cycle that could operate continuously, condensing and reusing its volatile fluids without waste, though his prototype never succeeded commercially.
The Dunedin sailed for London on the 15th of February 1882 carrying frozen meat from New Zealand, the first commercially successful refrigerated shipping voyage. Within five years, 172 shipments of frozen meat were sent from New Zealand to the United Kingdom.
General Electric released the Monitor Top, the first refrigerator to run on electricity, in 1927. Earlier, in 1911, GE had released a household unit powered by gas.
Frigidaire synthesized Freon in 1930, a refrigerant based mostly on chlorofluorocarbon chemistry that made refrigerators smaller, lighter, and cheaper. The average price dropped from 275 dollars to 154, allowing household ownership in America to exceed 50 percent by 1940.
Refrigeration, along with reliable automobiles, highway systems, and agricultural production increases, allowed galactic cities such as Los Angeles, Las Vegas, Houston, and Phoenix to grow in places with no river, harbor, or valley crossroad. These sites would have been uninhabitable a few hundred years earlier without a way to cool air and transport food and water over great distances.