How does the altimeter react when the temperature is cooler than standard conditions?

When the temperature is cooler than standard conditions, the behavior of the altimeter is influenced by the fact that cooler air is denser than standard air at the same pressure level. This means that the aircraft is actually at a lower altitude than what the altimeter indicates. Since altimeters are calibrated based on the assumption of standard atmospheric conditions, which include standard temperature, a cooler temperature will cause the altimeter to read higher than the actual altitude.

In essence, when the atmosphere is colder, the air pressure at a given altitude is higher than it would be under standard conditions, leading to an erroneous reading. The altimeter measures pressure, translating it into altitude, and if the air is colder, it assumes the plane is at a higher altitude than it actually is. Therefore, when faced with cooler temperatures, a pilot must be aware that the altimeter is likely overestimating altitude, hence the statement that it reads higher than actual altitude is accurate.