The speed of sound in air increases by approximately 0.61 m/s for each 1°C rise in temperature. At 0°C, sound travels at ~331 m/s; at 20°C it is ~343 m/s. The relationship is: $v = 331 + 0.61\,T$ where T is temperature in °C. This increase occurs because higher temperature increases the average kinetic energy of air molecules.