Egg-laying hens in a typical battery cage facility. | Getty Images Popular conceptions of farming tend to associate good animal welfare with environmental virtue — an intuition so strong that researchers have described a “humane halo” effect, where consumers who are told that a farm uses better environmental practices also assume that it treats its animals well. So it might come as a surprise to hear that one way of making eggs better for the planet might be to make life a whole lot worse for the chickens who lay them. This, anyway, was the apparent upshot of a controversial and widely discussed new paper on the environmental impacts of different egg farming systems. Cage-free, free-range, and organic eggs, it found, are higher in greenhouse gas emissions, land use, and other environmental harms than confining hens in tiny cages. Consider the implications of that result: At any given moment, more than 8 billion egg-laying hens inhabit farms across the planet. The vast majority of them live in wire cages that severely restrict basic movements like spreading their wings and turning around. They barely have room to move around at all, which can induce depression-like states. “Hens represent the largest population of terrestrial animals housed in cages throughout their lives,” as the new study puts it. In animal agriculture, there is an unfortunate and well-known trade-off between environmental impact and animal welfare because, all else equal, animals who are allotted a bit more room to roam and express natural behaviors take up more resources. (Of course, that trade-off disappears if we simply replace animal products with plants.) That is why almost all animal products these days are produced on factory farms in the first place — factory farming doesn’t exist merely to be evil, but rather because it’s efficient, and the cost of efficiency is borne by the animals. Inside this story A new study found that eggs from caged hens have a smaller environmental footprint than cage-free eggs. But critics say the study relies on outdated data and may exaggerate the climate gap. Cage-free farming is far from cruelty-free, but it gives hens substantially more freedom than extreme confinement in cages. And eggs account for such a small share of global emissions that the climate cost of going cage-free is relatively minor. The bigger issue is what happens when we treat carbon efficiency as the ultimate arbiter of our values. Modern egg production has been optimized to extract extraordinary productivity from chickens, often at enormous cost to their bodies and well-being. For consumers, there’s a way around the climate-versus-welfare trade-off: Plant-based foods have lower emissions than eggs without requiring animals to suffer for their production. Although the new paper may overstate the magnitude of this tension for eggs (more on that in a moment), it’s directionally right: Hens who are able to walk, flap their wings, fly, and perch will eat more calories than those trapped in cages, so their environmental footprint is generally going to be greater. But here is the thing: That doesn’t really matter. Eggs aren’t generally singled out by climate experts as a major decarbonization priority. Although animal agriculture is a significant contributor to climate change, making up about 12 to 20 percent of global greenhouse gas emissions, eggs are responsible for a very small share of that — about 3 percent of all livestock emissions. As a back-of-the-envelope estimate, that is, on the high end, roughly 0.6 percent of all emissions. I think we can spend a tiny bit of our carbon budget to spare billions of animals a life of near-total immobilization. But it’s weird to think about this as an environmental question at all. Chickens aren’t merely resource burdens — they’re inhabitants of our planet who deserve to share in the benefits of a more sustainable future, too. And the most salient feature of caging hens is not that it’s marginally more environmentally optimized, but simply that it’s wrong. Caging humans would reduce our emissions, too, as Lewis Bollard, managing director for farm animal welfare at the philanthropy Coefficient Giving, grimly remarked about the paper. No one would ever suggest doing that, because a lower carbon footprint cannot turn a morally indefensible practice into a good idea. Is there really a climate case for cages? Over the last few decades, animal welfare advocates have sought to bring hens some relief from extreme confinement, passing laws that ban cages and persuading grocery stores, restaurant chains, and other food purveyors to source cage-free eggs. (When I was in college, I worked on one of these campaigns, helping convince my school to serve exclusively cage-free eggs in its dining halls.) Nearly half of egg-laying hens in the US and two-thirds of those in the European Union are now raised cage-free, and four-fifths of eggs in the UK come from cage-free hens. But cages still prevail in some high-income countries, including Canada, Japan, South Korea, and Israel. This advocacy work has spread to low- and middle-income countries, too, where most of the world’s hens live and overwhelmingly remain caged. Cage-free eggs are still far from cruelty-free, but they likely represent a meaningful welfare improvement. View Link The new paper, published in Royal Society Open Science late last month, used data from the UK to compare the impacts of five different egg farm types: battery cages, slightly larger “enriched” cages, cage-free indoor barns, free range, and organic free range. Fully indoor cage-free systems are by far the most widespread form of cage-free farming in the US and elsewhere in the world, and they’re generally the default large-scale system used in transitions away from cages, so they are our primary focus here. The researchers compared egg farming systems on four environmental metrics: greenhouse gas emissions, nutrient pollution in waterways, soil acidification, and land use. The lowest impacts across all four categories were found in farms that used enriched cages, which are one-third to two-thirds larger than the standard battery cages that dominate the global egg industry — the latter had the second-lowest impacts. (From an animal welfare perspective, enriched cages are akin to slightly loosening a straitjacket — only a grotesque starting point could make them look generous. They afford each hen a living space not much larger than a sheet of printer paper, well below the area typically needed to perform basic behaviors like flapping her wings and grooming herself.) To produce the same number of eggs, the study found, cage-free barns emit about 56.1 percent more greenhouse gases than enriched cages and 33.8 percent more than battery cages. The authors have said that the paper isn’t meant to advocate keeping hens in cages, but rather to inform decision-making about cage-free transitions with accurate estimates of the environmental trade-offs involved. The findings have been presented as relevant to food sustainability discussions globally, more broadly than just in the UK. And, Bollard pointed out to me, the paper has come out as the EU and UK weigh fully banning caged egg production, raising the possibility that its findings could influence those policy fights. “We recognise that the transition toward cage-free production is important for improving animal welfare,” lead author Oliver Martinić, who recently earned a PhD in animal and food science from the University of Padova, told me in an email. “The long-term goal should be to develop cage-free systems that combine high standards of animal welfare with improved production efficiency and lower environmental impacts. If we can achieve that, the environmental gap between cage-free and caged systems could be substantially reduced.” It’s certainly important to have an accurate accounting of the environmental impacts of all types of farming. Whether or not the paper achieves that has been a subject of some debate. To make their calculations, the authors drew from data published more than a decade ago, but cage-free egg production has since become more environmentally efficient. “The paper is methodologically flawed,” Ilias Kyriazakis, a professor at Queen’s University Belfast and senior author of the earlier research whose data the new paper relies on, wrote in a critique of the study. “It relies on our data from 2010 to construct scenarios intended to represent national conditions in 2023, without adequately accounting for the substantial changes that have occurred over that period.” As a result, he added, “the authors are likely to have overestimated some of the impacts” of the non-cage production systems. The authors have said that they used that dataset because it’s the most comprehensive one available, and Martinić told me that “production systems have continued to evolve, so newer data would be valuable for assessing the extent to which the gap [between caged and cage-free eggs] has changed.” Other peer-reviewed research, meanwhile, has found a smaller gap in climate impacts between caged and cage-free eggs. Even the makeup of hens’ feed may matter more for the climate impact of eggs than whether they’re kept in caged or cage-free housing: One US study found that cage-free farms were lower in emissions and other impacts because they used more environmentally efficient feed. In the end, these differences may not be that big of a deal because the climate impact of eggs is small in the grand scheme of animal agriculture. Using the new study’s own emissions estimates for eggs, a single beef burger emits as much as about five dozen cage-free eggs. “There’s no doubt that eggs are the least environmentally impacting animal product per unit,” Kyriazakis told me. So when considering whether caged or cage-free eggs are better for the world, their environmental impact is not very high on the list of things to agonize over. View Link Martinić and his co-authors don’t ignore animal welfare entirely — they attempt to account for it, but they have an oddly narrow way of doing it. The paper’s welfare metrics leave out what it is actually like for a hen to live inside a cage. Instead, its chosen measures score cage systems more favorably, because the model assumes that they have lower mortality rates, and they require fewer total birds to produce the same number of eggs. The result is that cage farming ends up looking comparatively better on welfare, though the authors themselves acknowledge that their analysis leaves out many indicators of welfare and “should be interpreted with caution.” (Critics of the study have noted that its mortality numbers are more than a decade out of date, and that recently, as egg producers have learned to better manage cage-free farms, the gap in mortality rates has declined.) Beyond the carbon ledger There is a term for what happens when we reduce our biggest social problems to environmental or climate ones, and lose sight of everything else at stake: climate reductionism. The new paper and discourse surrounding it display how that trap can shape the way we understand and treat nonhuman animals. It also reflects a long-established tendency in animal agriculture research to view animal welfare through the lens of efficiency and productivity, rather than through the desires of the animals themselves. To contend more deeply with the ethics of mass-producing animals like egg-laying hens for food, we have to momentarily cast aside questions about efficiency and ask, what is life like for a hen from her own perspective? I happen to know a lot of chickens — in the right circumstances, they’re convivial, spirited, energetic animals. The widespread myth that they’re stupid has more to do with our own repressed guilt than with the animals’ capacities. Their experiences call on us to face not just the cruelty of cages, but also to look beyond cages to problems common to all forms of egg farming. To name just a few: Egg-laying hens have been bred to channel their bodily resources into laying extraordinary numbers of eggs, which takes a heavy toll on their bodies, depleting their skeletons of calcium, and making them prone to painful bone fractures and reproductive disorders. (The red junglefowl, the wild animal equivalent of the chicken, lays 10 to 15 eggs per year; farmed hens lay more than 300.) On cage-free farms, meanwhile, escaping the cage does not mean entering anything resembling a natural environment. Rather, the hens live in crowded, polluted, sometimes windowless sheds filled with thousands or tens of thousands of other chickens, where unnaturally large, dense social groups can intensify injurious pecking and other aggression. They are ultimately killed once their productivity wanes. These conditions have even fueled a vigorous debate in the animal advocacy movement over whether pushing for cage-free eggs is a good idea at all, because they can give the public the false impression that the worst parts of egg factory farming have gone away. But cages are only one part of that system — modern animal agriculture is defined by a complex set of practices optimized to squeeze as much productivity out of animals as possible. Challenging more fundamental features of egg production, like the genetics of modern laying hens, would be harder than eliminating cages because it poses a deeper challenge to the value the industry elevates above all else: efficiency. We would have to demand less of their bodies, and that would very likely make each egg more expensive and more emissions-intensive. What, then, does that mean for you? On an aggregate, societal level, I think cage-free reforms have been a good thing, because they have made a terrible system that we can’t simply wave away with a magic wand less bad. But more profound change will require consumers to demand something more than cheap animal products. So if I’m addressing you, an individual, I’d say something different. The most obvious win-win is hiding in plain sight: Plant-based foods like tofu and beans are significantly lower in emissions than eggs, while avoiding the moral costs of egg production altogether.