Image: Shefaet, Flickr
This one goes out to mig. Mig wrote us and explained that yesterday a distant facebook friend posted this:
"Oceans are the single largest CO2 reduction system in the world. Water Vapor is the biggest contributor of CO2 in the atmosphere and 97% of all CO2 in the atmosphere comes from natural sources, not man made."
Mig says: "Now, i'm not a scientist and don't know enough about all of this to debunk or confidently argue the point or the source. Have you heard of this?"Well. That got a bit of a conversation going. On a simplistic level, this facebook myth is easy to disprove. After all, water is H2O (H - O -H). CO2 is O - C - O. Therefore, water vapor is NOT the biggest contributor of CO2 in the atmosphere. Q.E.D.
The Real Question
However, on a deeper level, this question cannot be answered without re-interpreting the comment. This example clearly highlights the difficulty of addressing scientific topics in a society with a depressingly insufficient science education. The fact is that the term "CO2", or worse "carbon" has become a synonym for "greenhouse gas". So the facebook comment really translates to:
"Water Vapor is the biggest contributor of greenhouse gases in the atmosphere and 97% of all greenhouse gases in the atmosphere comes from natural sources, not man made."
Mig asked for a source and was given this: Global Warming: A Closer Look at the Numbers. And sure enough, this source sets out an argument that when water vapor is taken into account, the man-made contributions to global warming amount to only 0.28% of the greenhouse gases in total.
Busting the Myth
So does that prove that global warming is a big lie? That scientific "tricks" are being used to blow it all out of proportion? No. It does not. Mig, we suggest you use an analogy that your friend can understand to debunk the implication. For example, think about it this way: the 1800 calories a person eats per day (on average) are the main factor in maintaining a healthy weight. If you eat only 0.28% more calories every day than you need, you will gain over 1/2 a pound per year. In a linear model, you would find yourself 30 pounds overweight at age 60.
Similar to global warming, though, a reasonable model must account for additional factors. Your appetite to eat even more as you put on the pounds is similar to the increased emissions of greenhouse gases as populations in developing countries grow richer. The metabolic effect of being overweight, which speeds up the rate of weight gain, is similar to the effect of man-made CO2 causing warming which causes even more water vapor to stay in the atmosphere and the earth to warm even faster. Add these factors to the weight-gain model, and you could argue that 60 years of 0.28% extra calories causes extreme obesity.
This analogy is a very simple version of how models work, trying to take a large number of factors into account and predict an outcome. Models are notoriously susceptible to the assumptions and starting points. But you can rest assured that although some graphical depictions of information may neglect water vapor, the importance of water vapor is fully addressed in climate models. And even if man-made contributions to increased greenhouse gases appear to be a miniscule part of the whole picture, the fact is that the models show a grim picture if humans continue to put a little bit more greenhouse gas into the skies than nature intended. Moreover, a preponderance of the world's scientists who understand the complex issues and the models agree that the man-made greenhouse gases are a problem.
When our own ability to analyze and understand the details of a situation fail, we are left to fall back on our value judgements. Which brings me to one final arrow in your climate change myth-busting quiver: you may not understand the complex science. But you can look at the process. When a lot of the world's scientists voluntarily come together and democratically back a dire message to the world's population, perhaps we should sit up and listen.