Does breathing contribute to climate change? With every breath we take, we breathe in oxygen and breathe out carbon dioxide. Carbon dioxide is a greenhouse gas. So are we contributing to climate change just by the act of breathing?
If someone knows a bit about biology, they might respond, “no, because new plants will replace the plants we have eaten, and the new plants will take up the carbon dioxide.” The actual answer is not some glib assurance that new plants will replace the old, but “it depends.” And when you spin out what precisely it depends on, it has very significant implications for how we address climate change.
Al Gore’s response is that “we are participating in a closed cycle. That is, the carbon we breathe out comes from the food we eat, whether directly from plants, which take it in via photosynthesis, or indirectly from meat. So we get carbon from plants, breathe it out, and they take it in again.” (From Gore’s latest book, An Inconvenient Sequel, based on the movie of the same title, p. 234.)
Gore almost gets it. Let’s start with that last reassurance: “we get carbon from plants, breathe it out, and they take it in again.” Oh, really? To be balanced, there must be a net addition of plant life to the planet for each additional human (or additional cow). Are we doing that, do you think? Human and livestock populations have each more than tripled just in the 20th century. Have we seen a corresponding increase in plant matter?
Each additional human on the planet increases the amount of CO2 breathed out. If this additional human goes vegan and dedicates their lives to reforestation, then the answer is yes — there will be plants there to take up that CO2. But if this additional human decides to raze the rainforest to make a few dollars, then no — the total amount of plant matter on the planet will stay the same or even decrease. Most of us, of course, fall in between these extremes. But if our economy contributes to increasing cows and devastating plant life on the planet (think: meat consumption, deforestation, overgrazing, soil erosion), then it has much the same effect.
Historically, humans have had a very significant negative effect on plant life. Vaclav Smil estimates that during the last two millennia, total plant phytomass on Earth has declined by 40% (and 17% just in the 20th century).
Yes, there is a cycle here, but it’s not a closed cycle. We have disrupted it by destroying the plant matter on the planet, and through dramatic increases in human and livestock populations. We are not reutilizing all the CO2 that we (and our livestock) are breathing out. The biomass of large animals is now over seven times what it was just 500 years ago. We have upset the balance of nature.
These are the kinds of considerations that led Robert Goodland and Jeff Anhang to conclude that livestock contribute 51% of all human-caused greenhouse gas emissions. There are some legitimate scientific questions here, and we can debate whether the figure for livestock really is 51%, and not 35% or 65% or some other figure. Exactly how much CO2 does each human (and each cow) breathe out? How many cattle are there in the world, in the first place? How accurate are Smil’s estimates of the decimation of plant life?
However, this is not primarily a scientific issue. It is a logical issue, and most people (including Gore) who minimize the impact of livestock on climate have failed to even consider the impact of livestock and human population on the biological carbon cycle. When you multiply our net impact on the biological carbon cycle by the millions and billions of people and livestock animals on the planet, it’s going to be very significant. It should really be the centerpiece of the climate change discussion, not just a side issue.