Perhaps the easiest way to mislead your audience, or indeed yourself, is to generate deceptive graphics. Murry Salby is to be saluted for his mastery of this art, with several fine examples in his recent London lecture. Here are the best two.

The first example is a figure showing the changes in atmospheric ^{14}C due to atmospheric nuclear bomb testing and the subsequent absorption of this ^{14}C into the oceans and biomass. Salby is arguing that this occurs quickly.

“Within two decades the nuclear surplus of

^{14}C was history”

Bomb-radiocarbon is a useful dating technique over the last 60 years, so I am familiar with the general shape of the curve and something is wrong with Salby’s figure – it shows atmospheric ^{14}C to have declined to its original value within 20 years of the 1963 test ban treaty. In reality, ^{14}C concentrations remain above background 50 years later. Comparing Salby’s version with the correct data, it becomes obvious (OK, Cathy worked it out first) what he has done.

Rather than showing the whole curve, Salby starts his curve in 1958 after many bomb tests have been conducted. His background level of ^{14}C is therefore much higher than the true background level. This makes it appear that the bomb ^{14}C moved out of the atmosphere much faster than it really did. These shenanigans would have been obvious had he extended his figure to the present day as he would have had negative ^{14}C values, and the poor fit of his exponential curve would have been exposed.

Salby’s claim that ^{14}C levels declined to background within 20 years is bogus, his graph is exceptionally deceptive.

The second example is a figure Salby uses to argue that emissions are a function of population as the two curves overlie each other since 1860. If we accept this claim, it implies that population control rather than emissions abatement is needed.

There is just the little problem of the scale of the two curves. The emissions scale starts at zero, the population curve starts at about one billion. The two curves only overlie because of this scaling trick. A fair plot would show that emissions have risen much faster than population, over this time period. Does Salby really think that per-capita emissions in 1860 (horse-drawn ploughs, etc) were equal to those of 2010? The data suggest otherwise.

Is Salby aware of his skill in constructing deceptive figures? Certainly his audiences are not.