Are Humans Causing Global Warming? Ask Floyd Landis.

Blog Post for Columbia University Press

The earth is warming. But can we be sure that humans are the cause? Yes. The same way cycling officials were sure that biker Floyd Landis doped with synthetic testosterone while winning the 2006 Tour de France.

With Lance Armstrong retired and most of the other top riders expelled for illegal drug use, Landis had become one of the favorites. He was leading when in stage 16 he fell to eleventh place. Then, just as his chances of winning seemed dashed, Landis won the next stage going away and went on to ride the Champs-Élysées in the winner’s yellow jersey.

A few days later, Landis’s team announced he had failed a test for banned steroids. Landis appealed the ban, raised an estimated $1M for his defense, and wrote a 300-page book titled, “Positively False: the Real Story of how I won the Tour de France.”

After years of denial, in 2010 Landis reversed himself and admitted that from 2002 through 2006 he had used a grab-bag of banned substances and methods. Why did he finally have to give up his denial? Because the carbon isotope test proved beyond reasonable doubt that he had doped with synthetic testosterone.

Testosterone is mostly carbon. Synthetic testosterone is made entirely from plants, which have a different carbon isotope ratio than our environment overall. The carbon in Landis’s body had the distinctive plant ratio, proving beyond reasonable doubt that he had doped with synthetic testosterone.

So how do scientists use the method to confirm that humans are causing global warming?

Since 1800, CO2 in the earth’s atmosphere has risen 40% and because of the greenhouse effect, warmed the planet. The obvious source of the added carbon is the 330 billion tons of carbon that burning fossil fuels has added to the atmosphere since the Industrial Revolution. Yet global warming deniers deny this obvious fact. Well then, let’s prove it.

First, coal, oil, and natural gas also come from plants and also have the distinctive carbon isotope ratio of plants. As CO2 in the atmosphere has built up steadily, its isotopic composition has shifted just as steadily in the direction of plant carbon. That tells us the added carbon is coming from plants. But what kind of plants? That question we can also answer.

One carbon isotope, C14, is radioactive and dies away to undetectable levels in 50,000 years or so. Fossil fuels, being millions of years old, have no C14 left. Adding ancient carbon should have lowered the proportion of C14 in the atmosphere—and it has. For the last 50 years, as the amount of carbon in the atmosphere has increased, its C14 ratio has fallen steadily.

Just as the carbon isotopes prove that Landis doped his body, they prove beyond reasonable doubt that humans are doping the atmosphere with ancient plant carbon, carbon from fossil fuels.

Unlike people, isotopes do not lie.