Granted, I believe the primary cause of obesity is due to the excess consumption of carbs - whether in the form of cakes, chips, sugary drinks, potatoes, or even those hearthealthywhole grains, and that the sheer volume of those foods available so cheaply these days is the biggest culprit in obesity and diabetes.

But I think that other more seemingly minor and more subtle changes in the food supply have also contributed to the problem.

For instance, HFCS could be considered a minor change in the food supply, because a lot of foods that are currently sweetened with HFCS were at one time sweetened only with sugar. People ate those foods, and didn't become obese on them. They also didn't eat as much of them as they do now, but the question is why do people eat so much more of those foods now?

Should the switch to HFCS have really made any difference, since HFCS only has 10% more fructose than sugar? Same number of calories, right? But it's not just the calories involved, it's the subtle difference in the number of calories readily accessible for energy. If you can't access that 10% because it's in the form of fructose instead of sucrose, it can cause you to hunger for enough readily accessible calories to make up for the slight energy shortfall. And then hunger even more when the insulin kicks in, at which time you're eating even more HFCS laced foods, which results in even more fat storage and less readily accessible energy than you were used to experiencing.

So I don't think it's too much of a stretch to think that if every single food we eat is becoming even very subtly more and more nutritionally inferior as the CO2 levels rise, that we will tend to eat more and more in order to make up for the nutritional shortfall, thereby becoming just another small part of the cause of obesity.