Is a planet full of exhaling humans contributing to global warming?

This week's question comes from George Nelson in Kelowna, British Columbia. He asks:

Is human respiration a significant factor in the rise of CO2 levels in the Earth's atmosphere? Increased population would seem to result in increased levels of CO2 in the atmosphere but is it significant in relation to other sources?

Bruce Sutherland, a professor of physics and Earth and atmospheric science at the University of Alberta says the answer to this question is no. The mass of carbon dioxide exhaled by the more than 7 billion people on Earth is estimated to be about three gigatons per year. That is less than one-tenth the mass produced each year by industry. 

But in fact even this is misleading, because our respiration is actually "net zero" emissions.  Everything we are made of, including the carbon dioxide we breathe out, is a result of eating plants, either directly from eating vegetables or indirectly from consuming meat. And plants take CO2 out of the atmosphere and convert it to oxygen.

So when we exhale carbon dioxide, we are simply putting back what was taken out when the plants we're made of were growing, so breathing is effectively carbon neutral. 

Respiration aside, Sutherland suggests the larger issue is that a growing human population means more people are using fossil fuels, which does contribute to climate change.