"THAT'S DEPRESSING!" remarked a preservice teacher about the likely consequences of China and India achieving the energy-intensive lifestyle of the United States. She had just been looking at the record of average surface temperatures of the Earth. The year 1998 was the warmest since reliable temperature records have been kept, and the twentieth year in a row in which the average global surface temperature was higher than the 119-year average. The next year, 1999, was the fifth warmest on record; the six warmest years on record have occurred in the last decade.(1)
If the global warming trend continues, the results could be depressing indeed: melting polar ice along with thermal expansion of the oceans could raise the sea level, flooding coastal cities, and many agricultural landscapes could dry out, becoming deserts. And yet, as the class studied the issue further, we learned that the news is not all bad. The nations of the world have already taken collective action to solve one global atmospheric problem: depletion of the ozone layer. Global warming, as we will discuss below, is a different and a bigger problem, but scientists have already come together to measure, understand the causes of, and set goals for reducing the rate at which it occurs.
The preservice teacher quoted above was attending our college course on the value of Science-Technology-Society (STS) education for middle and upper elementary students. Social studies teachers have called for meaningful learning in social studies that is issues-centered, connects to students' lives, and provides opportunities for action taking.(2) We have developed a unit of study on global atmospheric change for school students, in the hope that teachers will find it useful to include this STS issue in their curriculum.(3) Global warming and ozone layer depletion exemplify the possibilities that await when teachers bring STS topics into the social studies classroom.
The STS movement, as it was advanced during the 1980s (largely due to Project Synthesis), challenged social studies teachers to prepare students to be scientifically literate as well as socially conscious.(4) The issues of global warming and ozone layer depletion are central to "Education for Citizenship in the 21st Century" and correlate closely to four of the ten strands of the NCSS social studies standards: (III) PEOPLE, PLACES, AND ENVIRONMENT; (VIII) SCIENCE, TECHNOLOGY, AND SOCIETY; (IX) GLOBAL CONNECTIONS; and (X) CIVIC IDEALS AND PRACTICES.(5) The purpose of this article is to describe some of the basic science that underlies the issues of global warming and ozone layer depletion, elaborate the rationale for including these issues in social studies, and provide related suggestions for social studies instruction. This information has been synthesized from comprehensive analyses published by scientists working together in large collaborations, and from works by the authors.(6)
Global warming and ozone layer depletion are two different problems (see the sidebar "Misconceptions about Global Atmospheric Change"). Global warming is caused by the "greenhouse effect," which is essential to life as we know it on planet Earth. Electromagnetic energy coming from the sun is absorbed by the Earth, which radiates some of this energy outward as infrared energy (heat). Some of this infrared energy escapes into space, but much of it is absorbed by "greenhouse gases" in the lower atmosphere (the troposphere) and is radiated back to the Earth as heat energy.
The greenhouse effect, then, is a warming of the Earth's surface that makes it hospitable to life. Without the greenhouse effect, the surface of the Earth would be a frigid -100 [degrees] F. Alternatively, a "runaway" greenhouse effect, like that found on the planet Venus, would result in a surface temperature of 900 [degrees] F or more. Greenhouse gases, including water vapor ([H.sub.2]O), carbon dioxide ([CO. …