They’re part of a carbon cycle, not a carbon source.
If you will excuse a mixed metaphor, cows are being used as scapegoats to downplay and detract from the driver of the climate crisis — fossil fuels. The claim is that cows burp methane gas and contribute to our climate crisis. This is a deception, because it leaves out important parts of the equation.
To summarise, cows and other ruminants are part of a carbon cycle, whereas the fossil fuel industries are a carbon source.
The word cycle comes from the Greek for circle, and that’s what is going on. Radiant energy from the sun (a near-limitless external energy source) powers plant photosynthesis, converting CO2 and water to carbohydrates (such as cellulose, sugars), that the plants have various uses for including building themselves and growing. When ruminants eat the plants they take in the carbon-containing carbohydrates. At this stage, the ruminant is a carbon-sink, not a carbon-source. The carbon in its rumen came from CO2 in the atmosphere, via the plant.
As byproducts of energy metabolism and microbial fermentation, the ruminant produces CO2, methane (CH4) and water vapour, which are returned to the atmosphere. No carbon is created by the ruminant in this process — that would violate fundamental laws of chemistry and physics. The CO2 breathed out by the ruminant is available for ongoing plant photosynthesis. After a few years, the methane breaks down to CO2 and is also available for re-uptake. Meanwhile, ruminants graze on new plant growth, and so it goes on.
In fact, so it has gone for millennia by ruminants that preceded modern cattle (bison, buffalo, wildebeest etc), without an accumulation of greenhouse gasses in the atmosphere — carbon is being drawn out of the atmosphere by plants, taken up by ruminants, then returned to the atmosphere to repeat the cycle. This is nature in balance, as it has always been.
There are even some analyses indicating that, if farmed regeneratively, cows could contribute to carbon sequestration, such as by fertilising healthy grasslands and promoting their regeneration. As well, plants can sequester carbon in the soil, directly through their roots to feed symbiotic micro-organisms, or indirectly from the decay of organic matter.
Over time-scales of hundreds of millions of years, organic carbon-rich deposits in the soil formed sediments that we now harvest as coal. Meanwhile, oil formed from sediments on the ancient sea floor, comprising dead and decaying plankton and organic matter. This oil, when heated by compression from an overlying buildup of sedimentary deposits or tectonic movement, could undergo a chemical reaction that released methane (and some other minor gasses), which in turn could be trapped as gas deposits.
Misleadingly, this methane is called natural gas. If natural gas was referred to as methane gas instead, it would put cow burps in perspective. Further, we don’t use the terms natural coal or natural oil.
By mining and burning these fuels, we are taking safely sequestered carbon out of the ground, and releasing it into the atmosphere as CO2, methane, or other greenhouse gasses. We are adding carbon to the atmosphere, without having a way of removing it. We have created a new source of atmospheric carbon, and created a climate crisis in doing so.
Nevermind the cows.