Biology Now, 2e

Amazon on Fire ■ 333

U.S.A.

Russia

4.8

3.3

U.K.

Brazil

China

India

World

2.9

1.8

2.0

0.7

1.6

If everyone in the world lived like the

average resident of this country...

...then this many Earths would be needed to

sustainably support us.

Near the equator, direct sunlight causes water

to evaporate from Earth’s surface. The warm,

moist air rises because heat causes it to expand,

making it less dense and lighter than air that

has not been heated. But as it rises, the warm,

moist air begins to cool. Because cool air cannot

hold as much water as warm air can, much of the

moisture from a cooling airmass is “wrung out”

and falls as rain.

For this reason, most tropical regions, includ-

ing the Amazon, receive ample rainfall. Earth

has four giant convection cells in which warm,