Atmosphere

The five layers

Temperature flips direction at every boundary — that is how the layers are defined.

• Troposphere

  All weather happens here; temperature falls to about −56°C (−68.8 °F) at the top.

  0–12 km

  ≈ 7.46 mi

• Stratosphere

  Ozone absorbs ultraviolet light and warms the air; jet airliners cruise near its base.

  12–50 km

  ≈ 31.1 mi

• Mesosphere

  The coldest layer, down to −90°C (−130 °F), where almost all meteors burn up.

  50–85 km

  ≈ 52.8 mi

• Thermosphere

  Extremely thin but up to 2,500°C (4532 °F); the auroras and the space station live here.

  85–600 km

  ≈ 372.8 mi

• Exosphere

  Atoms drift free and some escape to space; there is no real upper edge.

  600–10,000 km

  ≈ 6,214 mi

What the numbers mean

Small concentrations do enormous work.

• Carbon dioxide

  Up from about 280 ppm before industrialisation — a 50% rise in two centuries.

  ~424 ppm

• Water vapour

  The strongest greenhouse gas by total effect, and the fuel of every storm.

  0–4%

• Ozone

  A trace gas that filters the UV radiation which would otherwise sterilise the surface.

  ~0.00006%

• Pressure

  Air pressure halves roughly every 5.5 km (3.42 mi) of climb, which is why Everest needs bottled oxygen.

Did you know?

• If the atmosphere were scaled to the size of an apple, the breathable layer would be thinner than its skin.
• The boundary of space sits at 100 km (62.1 mi) — the Kármán line — and 99.99997% of the atmosphere lies below it.
• Air is heavy: the column above every square centimetre weighs about a kilogram, which is the air pressure you feel.
• Atmospheric rivers — narrow bands of water vapour — can carry more water than the Amazon River discharges.

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