S e c o n d e d I t I o n 1 Reading for the Real World 1

fossil fuels
(coal, oil, natural gas). CO
2
is considered the major cause of global warming on 
Earth. Other natural greenhouse gases include water vapor, methane (CH
4
), 
nitrous oxide (N
2
O), and ozone (O
3
). Additionally, several man-made gases are 
also thought to contribute to the greenhouse effect, namely chlorofluorocarbons 
(CFCs), hydrochlorofluorocarbons (HCFCs), and sulfur hexafluoride (SF
6
). 
Researchers have estimated that the atmospheric 
concentration
of CO
2
has 
increased by at least 30 percent since the 1800s. Industrial processes have also led 
to a 145 percent increase in CH
4
, and 15 percent increase in N
2
O in the atmosphere.
The buildup of these gases is believed to be the major cause of higher than 
normal average global temperatures in recent 
years. Consequences of such global warming 
could include higher sea levels, the spread of 
deserts in areas around the Earth’s 
equator
, and 
the drying up of fresh water sources.
In December 1997, at a United Nations 
summit on global warming in Kyoto, Japan, 
2
radiate --- to send out like light
10
fossil fuel --- fuel made from fossil remains of plants and animals
16
concentration --- the amount of a specific thing found in an area 
23
equator --- the imaginary line around the Earth at O(zero)º latitude
Track 19
 

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61
30
35
40
45
50
representatives from over 150 nations 
adopted
a treaty to 
limit emissions of CO
2
, CH
4
, N
2
O, HFCs, and SF
6
. 
The so-called Kyoto Protocol called for reducing emissions 
to at least 5 percent below 1990 levels of these gases by 
2012. The Protocol was signed by 38 industrialized countries 
attending the summit. Developing nations attending the 
summit were not required to