How does altitude affect temperature?
Most people think that the higher you go within Earth's atmosphere, the colder it gets. Well, they're right... kind of. In reality, the atmosphere is a complex thermodynamic system. One of the models describing Earth's atmosphere is the ISA (International Standard Atmosphere) model, which utilizes geopotential altitude to obtain the temperature.
According to this model, temperature either increases, decreases, or remains constant as you climb up in the atmosphere — contrary to pressure, which only decreases with higher altitude along with air density.
Why use geopotential altitude?
Geopotential altitude is used instead of geometric altitude (distance above a surface) because gravity on Earth is not exactly the same everywhere. It varies with height (Newton's law of gravity), latitude (due to centrifugal forces), and longitude (uneven distribution of Earth's mass). The conversion formula is:
H = (R × h) / (R + h)
where R = 6,356,766 m is Earth's effective radius for geopotential purposes. For most practical altitudes, the difference between geometric and geopotential altitude is very small.
Temperature vs. altitude chart analysis
The ISA 1976 model defines seven atmospheric layers, each with a specific lapse rate (rate of temperature change with altitude):
| Layer | Altitude Range | Temperature at Base | Lapse Rate |
|---|---|---|---|
| Troposphere | 0–11 km (0–36,089 ft) | +15°C / +59°F / 288.15 K | −6.5°C/km (−18.8°F/mi) ↓ |
| Tropopause | 11–20 km (36,089–65,617 ft) | −56.5°C / −69.7°F / 216.65 K | 0 (isothermal) |
| Lower Stratosphere | 20–32 km (65,617–104,987 ft) | −56.5°C / −69.7°F / 216.65 K | +1.0°C/km (+2.9°F/mi) ↑ |
| Upper Stratosphere | 32–47 km (104,987–154,199 ft) | −44.5°C / −48.1°F / 228.65 K | +2.8°C/km (+8.1°F/mi) ↑ |
| Stratopause | 47–51 km (154,199–167,323 ft) | −2.5°C / +27.5°F / 270.65 K | 0 (isothermal) |
| Lower Mesosphere | 51–71 km (167,323–232,940 ft) | −2.5°C / +27.5°F / 270.65 K | −2.8°C/km (−8.1°F/mi) ↓ |
| Upper Mesosphere | 71–86 km (232,940–282,152 ft) | −58.5°C / −73.3°F / 214.65 K | −2.0°C/km (−5.8°F/mi) ↓ |
Why does temperature decrease with higher altitude?
- Troposphere (0–11 km): This is the lowest part of Earth's atmosphere, heated by the Earth's surface. As you go up, you get further from the surface, and temperature drops by about 6.5°C per km (18.8°F per mile).
- Tropopause (11–20 km): In this transition layer, the temperature remains constant at −56.5°C (−69.7°F).
- Stratosphere (20–47 km): Here, temperature actually increases with altitude. UV absorption by the ozone layer produces this heating effect (+1.0 to +2.8°C per km).
- Stratopause (47–51 km): Another isothermal layer at approximately −2.5°C (27.5°F).
- Mesosphere (51–86 km): Temperature decreases again (−2.0 to −2.8°C per km). This region is difficult to study — aircraft can't reach high enough, and atmospheric drag renders satellites unusable.
- Mesopause (~86 km): The coldest place in Earth's atmosphere. Temperatures around −87°C (−125°F) and can drop as low as −100°C (−148°F).
Example: Temperature at 35,000 feet altitude
Commercial aircraft typically cruise at 35,000 feet (about 10,668 m), which is in the Tropopause layer. Using the ISA model:
- Geopotential altitude: ≈ 10,660 m (slightly less than geometric)
- Temperature: ≈ −56.5°C (−69.7°F / 216.65 K)
- Layer: Tropopause (isothermal)
This is why aircraft cabins must be pressurized and heated — the outside air is extremely cold and thin.
Frequently Asked Questions
Is this calculator accurate?
This calculator uses the ISA 1976 (International Standard Atmosphere) model, which is the internationally accepted standard used in aviation, aerospace engineering, and meteorology. Real-world temperatures can differ due to weather, seasons, and geographic location, but the ISA model provides an excellent baseline approximation.
What is the maximum altitude supported?
The ISA 1976 model extends to 86,000 meters (approximately 282,152 feet or about 53 miles altitude). Beyond this, the model is not defined.
What does lapse rate mean?
The lapse rate is the rate at which atmospheric temperature decreases (or increases) with altitude. A negative lapse rate means temperature decreases as you go higher; a positive lapse rate means temperature increases. An isothermal layer has a lapse rate of zero.
Why do commercial planes fly at around 35,000–40,000 feet?
At this altitude (in the tropopause), the air is very thin (low density), which reduces aerodynamic drag and allows jets to fly more fuel-efficiently. The temperature is stable (isothermal layer), and there is less weather turbulence compared to the troposphere below.
What is geopotential altitude?
Geopotential altitude accounts for the fact that Earth's gravity varies slightly with location and height. It is a corrected altitude that allows for more accurate atmospheric calculations. For altitudes below 50 km, the difference between geometric and geopotential altitude is less than 0.5%.