No. 115 Understanding Visual Exhibits in the Global Warming Debate

Published March 3, 2008

With a lack of traditional science, partisans on both sides, and enormous consequences depending on popular opinion and political will, it is important that people understand the evidence in the debate over global warming. Unfortunately, most people do not have the time, desire, or ability to undertake an independent study of the issues. Recognizing this, advocates have “packaged” their evidence with charts, graphs, and other visual exhibits designed to have maximum impact with minimal effort on the part of the public. These displays, while appearing to present hard facts, are often misleading.

Environmental activists may be tempted to exaggerate their case in order to convince the public and politicians of the validity of their scenarios. This was illustrated in a statement made by climatologist Stephen H. Schneider, one-time adviser to Vice President Al Gore and author of the book Global Warming: Are We entering the Greenhouse Century? (1989). Schneider said that in order to reduce the risk of potentially disastrous climatic change, “we have to get some broad-based support, to capture the public’s imagination. That, of course, entails getting loads of media coverage. So we have to offer up scary scenarios, make simplified dramatic statements, and make little mention of any doubts we might have.”

The manipulation of visuals–bar and line graphs, pie charts, even photographs–has proven to be a highly effective way “to offer up scary scenarios” … and it is easily done. This report explains how visuals can be manipulated by, among other techniques:¬†changing the appearance of graphs by adjusting baselines (minimums) and maximums on the vertical axis, selectively reporting data on, for instance, a time line appearing on the horizontal axis of a chart, using color and three dimensions to call attention to specific elements of a graph, even when those elements may not warrant special treatment, and inaccurately superimposing graphs with different scales.¬†

More than a dozen visuals throughout this report, including many that are common to the current debate over global warming, make it easy to see the effect of manipulated visuals.

Graphics can be used to summarize vast amounts of data, and they help convey a strong visual image: That is, after all, their purpose. But graphics can easily mislead … and all too often in the global warming debates, that too has been their purpose.