TEACHING A MOVING TARGET

In some fields of science, progress is slow enough that instructors and textbook writers have little trouble keeping up with the prevailing consensus. In others, such as the very public and contentious issue of global warming, such is not the case. During the last two decades, the science community's assessment of the global warming issue has formed a constantly moving target (but one steadily moving toward a greater human role). In 1988, Jim Hansen famously made the case in congressional testimony that global warming was underway and would likely be very large in the future, but many climate scientists regarded this claim as bold and premature, in part because the small global cooling trend of the 1950's-1970's had only turned to a warming trend a decade earlier. By 2000, after more than a second decade of rapid warming, community support for Hansen's conclusion had grown, but contradictory arguments remained. At that time, increased solar irradiance was thought to explain as much as 30% of the warming trend registered by surface stations; anthropogenic carbon aerosols were thought to have further enhanced the warming at Earth's surface, leaving even less of the warming to be explained by greenhouse gases; and (most importantly) satellite data spanning two decades showed no warming trend. As of this year, these arguments against global warming have largely collapsed, and most (but not all) climate scientists accept global warming as a reality that humanity must address. Through the rapid evolution of scientific opinion during the last two decades, the problem for instructors (and textbook writers) has been to address the evidence in this contentious issue in an objective manner. This talk will provide a sense of past challenges in dealing with this 'moving target'.