In one segment of his film "An Inconvenient Truth," Al Gore stands in front of a huge graph comparing the amount of carbon dioxide in Earth's atmosphere over the past 650,000 years with average atmospheric temperature, based upon data from Antarctic ice-core samples.
The top line shows the level of carbon dioxide. The bottom line shows the temperature.
There is an obvious correlation between the peaks and dips of the lines of data especially evident in the larger-scale movements corresponding to the last seven major ice-ages and inter-glacial periods. Carbon-dioxide levels and temperature levels have clearly coincided.
Okay. So far, so good.
But where's the base-line of the y-axis? What does that line represent in real numbers, or percentages? The baseline is not zero. The quantities on record vary between about 200 and 300 parts-per-million and the baseline is at about 150. This presents an exaggerated illustration of the rise and fall of the greenhouse gas.
One might rebut that this does not change the mathematics and it doesn't; but it is deceptive, and it does change perception in a film that is intended to change perception (and, purportedly, to inform.)
At about ten and a half minutes, Gore steps back from center-stage and plays a short cartoon that employs confused metaphors and bad graphics, and features a kid who talks like an idiot, bemoans her dad's alcohol abuse and is demeaned by a man of ambiguous identity. Gore then walks back to the podium smiling like that was pretty funny.
Any percentage of change can make a dramatic line on a chart if you cut a baseline high enough. Look it went from here to there! But where is zero? The line may not cut so dashing a figure if the axis proceeded from zero....
And, even if the graphic for carbon dioxide is accurate (within its "chopped-baseline" realm,) that for temperature cannot be. For this graphic, there is not even a pretense of real enumeration no quantification of the "y-axis" movement. No mathematical skills are necessary to know that "no numbers" is no numbers.
Worse, the temperature graphic dips nearly to the bottom of the screen during some of the colder periods. This would seem to chart an Earth temperature that has descended to near the freezing point on several occasions. At no time has the Earth's average atmospheric temperature been anywhere near the freezing point. The baseline is a chosen one the magnitude of peaks and valleys is elected, and unspecified.
Gore proceeds to bung it up even worse.
The purpose of this chart, initially, was to show the correlation between rises and drops in atmospheric CO2 and average global temperature "look, there it is." And there it is, indeed.
So far, the disparity between apparent statistical movement and real statistical movement, while somewhat faith-shaking, and moderately unethical, has been only slightly annoying one would hope for something more meticulous....
Near the beginning of the film, Gore's huge graph depicts one little spike in the CO2 line which tilts backward in a graphic depicting the increase of CO2 in time.
It is impossible that this depiction is accurate and nearly impossible to believe that it's there. But it is there.
See image, top right, courtesy of a reader.
Then Mr. Gore uses the same chart to make a "wow-factor" point about how much atmospheric CO2 quantities are likely to rise, predicted by current models.
He walks along the wall chart, gets on his hi-lift vehicle, and jokes while ascending alongside the rising line on the right side of screen, which trends upward sharply.
"Now, it's here" he notes, pointing to a dot on the line far above the highest peaks in known Earth history.
Where? He doesn't say. (Remember that we already know that his baseline is at 150, and so any vertical depiction is going to be proportionally exaggerated.)
Then he goes on to show where the CO2 level is going to be in 50 "or even fewer" years... thus de-specifying the timescale of this graph of no specified proportion.
Naturally, Al Gore's gawkiness does not detract from the dramatic importance of global warming, nor argue against the theory that human activity is an important factor.
Indeed, global warming science indicates that in the case of some stats, a percentage point or two can decide the future of oceanside cities.
There's no need to manipulate the statistics, and plenty of reason to not bungle them.