54
resembles how a greenhouse holds the sun’s heat to keep plants
warm all year long. Two other gases, water vapor and methane,
also have heat-trapping capability. Together, these greenhouse
gases linger in the atmosphere to regulate earth’s temperature
like a natural thermostat, which keeps the climate in balance.
Without greenhouse gases the planet would be too cold for hu-
mans and other living things to survive. If too high a concentration
of these gases builds up in the atmosphere, earth would grow too
hot to support life. Although both of these are extreme scenarios,
climate scientists are alarmed at what is currently happening to
the climate—and what it could mean for earth’s inhabitants.
Motorists make slow progress
on a typical Los Angeles freeway.
Gasoline- and diesel-powered
vehicles emit carbon dioxide, which
scientists around the world say is a
major contributor to climate change.
