agreement designed to protect the stratospheric ozone layer. The treaty was
originally signed in 1987 and stipulates that the production and consumption
of compounds that deplete ozone in the stratosphere—carbon tetrachloride,
chlorofluorocarbons (CFCs), halons, and methyl chloroform—were to be
phased out by 2000. Nearly 97% of ozone-depleting chemicals have been
phased out.GLOBAL WARMING
When sunlight strikes Earth’s surface, some of it is reflected back toward space
as infrared radiation (heat). Greenhouse gases absorb this infrared radiation and
trap the heat in the atmosphere.
Figure 11.2 The greenhouse effectTrends in Global Greenhouse Gas Emissions
The concentration of carbon dioxide in the atmosphere is naturally regulated by
numerous processes that occur in the carbon cycle. The movement (flux) of
carbon between the atmosphere and the land and oceans is naturally and
primarily regulated by: (1) the intake of CO 2 during photosynthesis; and (2)
being absorbed by seawater. However, these natural processes can absorb only