Blue Ice freezes nearby blocks

It IS the coldest ice. This is similar to campfires, but the exact opposite. Snow, ice, and other snowy biome features can be used this way.

Both campfires and blue ice blocks can have their range blocked using trapdoors and slabs, letting you build a makeshift AC/ heater. Grates improve the range but reduce the heating/ cooling effect.

Another block you could build would be the thermostat block. Depending on which side it receives a redstone signal from, it emits heat/ snow particles around itself. This also depends on the signal strength.