When Roger Friedman of Fox News said in his review of Al Gore's recent film on global warming, “It doesn't matter if you’re Republican or Democrat, Liberal or Conservative, your mind will be changed in a nanosecond,” he wasn't referring to scenes of Gore reflecting on the meaning of life before a slow-flowing river or even the images of glaciers collapsing or polar bears swimming in the open ocean in search of vanished ice. He was talking about a particular graph shown in the film that depicts the variation in temperature compared to the levels of carbon dioxide in the atmosphere over the last thousand years. Whether or not you accept the claim put forward in “An Inconvenient Truth” that the earth is getting warmer as a result of human activities will rest in large part on how you respond to this one slide. Not surprisingly, the graph and the data it represents have been the subject of a great deal of controversy. In fact, the “hockey stick graph” as it has been nicknamed because of its characteristic shape, may be the most contested example of information visualization in the history of science.

Figure 1: The original “Hockey Stick” graph from the Intergovernmental Panel on Climate Change Third Assessment Report showing the relationship between temperature and levels of carbon dioxide over the last 1000 years.

Critics of the graph play rough. The researchers responsible for the original data have been brought before Congress to defend their findings, with one member of the House going so far as to demand to inspect their personal financial records for evidence of bribery. Not only has the data been under the microscope, but the way that the data is represented has been minutely dissected. An article published by the conservative think tank the Heartland Institute calls the slide in Gore’s film, “A triumph of data manipulation.” Among other criticisms, the article claims that you can’t tell whether warmer temperatures precede or follow the rises in levels of carbon dioxide and that the scale along the vertical “y” axis is not clearly labeled. Rarely has an example of design been subjected to such intense scrutiny at every level from so many sources.

Figure 2: An image of slide from Al Gore’s presentation.

But why should one graph matter so much? The scientific reports on climate change must run into the millions of pages and nevertheless news organizations and pundits continue to, as one BBC headline put it, “Row Over Climate Hockey Stick.” Nancy Duarte and Jill Martin of Duarte Design, the firm that has been working with Al Gore since 2003 to create and refine graphics for the presentation shown in the film, declined to comment on the hockey stick itself, but they did provide a clue to the continuing obsession with the image. “Your brain is hardwired to process visually first and then verbally,” Duarte said, when putting together graphics for a presentation, “the goal is to communicate instantly. You're looking for impact.” This, then, is the “nanosecond” that Roger Friedman referred to in his review. Images and graphs can communicate immediately and, given the choice between words and images, we look to the images first. A recent survey by the National Science Foundation indicates that Americans are getting the message: Over 90% of U.S. adults have heard of global warming, with the majority considering it a “serious or very serious” problem. This is particularly impressive given the low rate of scientific literacy generally: 50% of U.S. adults don’t know how long it takes for the earth to orbit the sun.

According to Duarte Design, the key to creating an effective slide is including a convincing amount of detail while not distracting from the main message. “In general, you want to keep the visuals minimal and eliminate background noise to emphasize your point.” Making your point too forcefully may compromise credibility.

Figure 3: Alternate graph showing temperature is cooler now than it was during the Medieval Warm Period. By John Daly.

The graph above was offered by critics of global warming in an attempt to show that temperatures are not, in fact, on the rise. Because it lacks the level of detail of the “hockey stick” graph, it seems less creditable and less “scientific,” regardless of the validity of the data on which it was based. The issue of global warming seems complicated, and so we expect the graphs that represent it to seem complicated also. As Edward Tufte has famously observed, less is often just less when it comes to visualizing information. So designers should think twice before sacrificing complexity for the sake of clarity. “Complex information graphics correlate many data points in a way that conveys the overall message without sacrificing the nuance of detail or oversimplifying the concept,” says Martin. “Rather, they strike a balance between ‘thesis’ and ‘data’ levels of an argument and thus present a more robust and interesting case.” Although critics of the hockey stick have offered alternative visualizations, few of them have been as visually compelling as the original. The simplified graph below, which charts the same data, would only be convincing to someone who already agreed with the claim that the current pattern of global warming is part of the natural cycle.

Figure 4: Simplified graph showing temperature is cooler now than it was during the Medieval Warm Period. By David Wojick, PhD.

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