4. THE GREENHOUSE EFFECT (I)

  Life on earth depends on energy from the sun. About 30 percent of the sunlight that beams toward Earth is deflected by the outer atmosphere and scattered back into space. The rest reaches the planet’s surface and is reflected upward again as a type of slow-moving energy called infrared radiation.

As infrared radiation is carried aloft by air currents, it is absorbed by “greenhouse gases” such as water vapour, carbon dioxide, ozone and methane, which slows its escape from the atmosphere.

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