Biology Now, 2e

Amazon on Fire ■ 327

while the Southern Hemisphere simultaneously

experiences winter because it is tilted away.

Global warming, however, is not dependent

on how sunlight strikes the Earth. Instead, it

is caused by an increase in greenhouse gases.

Some gases in Earth’s atmosphere, such as

carbon dioxide (CO 2 ), water vapor (H 2 O), meth-

ane (CH 4 ), and nitrous oxide (N 2 O), absorb heat

that radiates away from Earth’s surface, prevent-

ing it from being released into space. These

gases are called greenhouse gases because they

South Poles (Figure 18.6). Where sunlight hits the

atmosphere more directly, its solar energy is more

concentrated. For this reason, more solar energy

reaches the equator, making it and neighboring

tropical regions much warmer than the poles.

Because Earth is tilted on its axis as it revolves

around the sun on its annual orbit, sunlight hits

different areas of the planet at different angles

over the course of the year. This is the cause of our

seasons: the Northern Hemisphere experiences

summer when Earth is tilted toward the sun,

1948

Trift Glacier, Switzerland

2002 2006

Figure 18.5

Consequences of climate change

Extreme weather and new rainfall patterns caused by climate change have led to increased flooding

in some areas and drought in others, bringing about ecosystem and habitat destruction, and species

extinction. The increase in global temperatures has led to melting of glaciers and polar ice, causing

sea level rise, increase in ocean temperatures, and coral reef bleaching and death. Effects on our food

sources include increased crop failure and depletion of important fisheries.

Q1: Name two ways in which climate change affects the frequency and severity of floods.

Q2: How has climate change caused a rise in sea level?

Q3: Give an example of an environmental effect of climate change in your state or region.