We can, though. By isolating contributing variables and comparing them to other options, we can isolate the ecological footprint of an animal per unit of body mass or useful produce.

We know how much methane cows vs other animals produce per unit of body mass, and we know cows are very high methane producers, even by ruminant standards - and cows are the most extensively farmed ruminants, too.

The carbon that enters the animal ends up either carbon dioxide, methane, or more complex carbon structures that can eventually become one or the other (and, over a very long term, it all eventually becomes carbon dioxide). Humans, for example, lean more on the carbon dioxide side, while cows emit a lot of methane. Advanced farms even use cow manure as a fuel source, though most of methane enters the atmosphere anyway. Natural decomposition of plants in the soil by soil bacteria is, in turn, less methane-emitting than either the processes happening in the rumen, or even in the human digestive system. Add to that all the maintanence overhead of cattle feed and farm management, and the differences will exacerbate even further.

Methane is a much more potent greenhouse gas, even when corrected for it's atmospheric lifespan, and hurts environment more than carbon dioxide.

All animals have more of such footprint compared to plant-soil bacteria cycle, but cows are exceptionally bad. This is why, from an ecological standpoint, beef and dairy consumption should be reduced, of not eliminated entirely.

The ALEPH 2020 initiative was launched in 2020, with the support of an interdisciplinary group of internationally recognized experts. The ALEPH acronym refers to Animal-sourced foods and Livestock: Ethics, Planet, and Health. ‘Aleph’ is also the first letter of the Proto-Canaanite alphabet, which later morphed into the Greek 'Alpha' and Latin 'A'. Originally, the letter was derived from the West Semitic word for 'ox' depicted in a Proto-Sinaitic glyph, obtained from an Egyptian hieroglyph showing a bovine head. As such, it not only represented a vocal sound and scriptural element, but also notions of strength, vitality, fertility, and generosity. Throughout (pre)history, animals (hunted or domesticated) and animal-sourced foods have always held these connotations.

Recently, however, there is a remarkable tendency to invert their original meaning, especially in the urban centres of high-income countries. Their consumption is increasingly being represented as unethical and harmful to both our health and the planet, to the point that some advocate a diet without or with only low amounts of animal source foods, and in some cases even the end of livestock farming.

We argue that these astonishing claims are not only counter-intuitive but also that their scientific foundations are misinterpreted and presented out of context. By addressing the topics of ethics (animal health), sustainability (planetary health), and nutrition (human health), we claim that livestock and the foods derived thereof have an important role to play in future food systems.

Here, for your convenience, the text on the page about what ALEPH is. Did you not look too far downwards?