In a well-argued essay, Jonathan Adler argues that libertarian environmentalists ought to take property rights seriously. No writer has had a greater impact on classical liberal and libertarian thinking about property than John Locke. It follows that any would-be free-market environmentalist must take Locke seriously. And not just Locke’s theory of property. His theory of government, as laid out in his 1690 Second Treatise, is equally important. In what follows, I will argue that considering Locke’s ideas on both property and government leads to conclusions that justify even stronger policy actions that Adler advocates.

Locke on property

Locke states the essence of his theory of property in this famous passage:

Though the earth, and all inferior creatures, be common to all men, yet every man has a property in his own person: this no body has any right to but himself. The labour of his body, and the work of his hands, we may say, are properly his. Whatsoever then he removes out of the state that nature hath provided, and left it in, he hath mixed his labour with, and joined to it something that is his own, and thereby makes it his property. It being by him removed from the common state nature hath placed it in, it hath by this labour something annexed to it, that excludes the common right of other men: for this labour being the unquestionable property of the labourer, no man but he can have a right to what that is once joined to, at least where there is enough, and as good, left in common for others.” (Chap. 5, sec. 27)

A few pages later, Locke makes it clear that the principle for acquiring property applies not just to acorns gathered in the woods, but to the land itself:  

As much land as a man tills, plants, improves, cultivates, and can use the product of, so much is his property. He by his labour does, as it were, inclose it from the common. (Chap. 5, sec. 32)

From these passages, we can distill three rights and three corresponding duties:


  • to property in one’s own person
  • to property in the fruits of one’s own labor
  • to property in land and natural resources taken from the commons by first use


  • to abstain from harming others in their persons
  • to abstain from taking or harming the property of others
  • to leave enough and as good for others when taking from the commons 

The rights and duties are inseparable; anyone who wants to claim the former is obligated to uphold the latter. 

These rights and duties were reflected in the English common law of Locke’s day. Violation of the duty not to harm others in their persons corresponds to the common law torts of assault (threatening or attempting to inflict offensive physical contact) and battery (carrying out a threat to harm). Violation of the second duty, when it pertains to personal property, is theft. Interference with others’ use of their land by knowingly entering it without permission is the common law offense of trespass. Actual harm is not an essential element of trespass – any interference with the owner’s right to exclusive possession and enjoyment of property qualifies. 

Locke’s third right is that of acquiring property from the commons by mixing one’s labor with it. Locke included the right to gather acorns from common land or to draw water from a stream, and also the right to take possession of unused land by “mixing one’s labor” with it, that is, plowing it, putting animals to graze on it, building on it, and so on. The broadest term to describe that process is acquisition by first use. When applied to land, the process was known in Locke’s day as enclosure, which calls to mind building a fence to keep out other people’s cattle or sheep, although a physical barrier would not be strictly required. Today, acquisition by first use is often called homesteading. I will use the terms “acquisition by first use,” “enclosure,” and “homesteading” interchangeably.

Over the years, acquisition by first use has sometimes been extended to abstract as well as tangible forms of property. For example, in the United States, in the early days of radio, the government reserved certain frequencies for marine and military use but left others up for grabs. As stations multiplied, interference became a problem. Courts determined that the first user of a frequency had homesteaded it and that use by others of the same frequency constituted trespass. That system, however, proved cumbersome and was replaced by today’s regulatory approach. (See Pablo T. Spiller and Carlo Cardilli, Yale Journal on Regulation, 1999.) 

Locke refers to the violation of his third duty—failure to leave enough and as good for others when taking from the commons—as engrossment. At that time, the common law applied that term to certain commercial practices that would now be known as “monopolizing” or “cornering the market.” Locke uses “engrossment” more broadly to include unjustly acquiring most or all of something at the expense of other holders of common rights. In one of his clearest statements on the subject, he writes: 

It will perhaps be objected to this, that if gathering the acorns, or other fruits of the earth, &c. makes a right to them, then any one may ingross as much as he will. To which I answer, Not so. The same law of nature, that does by this means give us property, does also bound that property too. … As much as any one can make use of to any advantage of life before it spoils, so much he may by his labour fix a property in: whatever is beyond this, is more than his share, and belongs to others. (Ch. 5, sec. 31)

Engrossment of land, as opposed to nuts or game, would occur if a person claimed more land than they could “improve, cultivate, or use the product of.” (Ch. 5, Sec. 32)

One implication of the engrossment proviso is obvious: The whole or a disproportionate part of the land cannot be enclosed, or privatized, by the first individual who happens to come along. (Think of a European explorer standing on the Atlantic coast of North America and claiming a swath of property that extends westward all the way to the Pacific.) Less obviously, it means that the “mixing one’s labor” principle can never be used to enclose the entirety of any commons even if each person who comes along takes only that modest amount that he or she can use personally. 

Instead, at some point, a scarcity constraint is reached beyond which enclosing even one more small parcel fails to leave “enough and as good for others.” Beyond that point, further enclosure may occur but, if so, it must proceed using some different mechanism that requires the consent of all who hold rights-in-common to the unenclosed remainder. In that regard, Locke contrasts the situation of a country like the America of his day, where he believed that unused or underused land existed in abundance, with that of England, where the scarcity constraint had already been reached. In the latter case, he writes, 

In land that is common in England, or any other country, where there is plenty of people under government, who have money and commerce, no one can inclose or appropriate any part, without the consent of all his fellow commoners; because this is left common by compact, i.e. by the law of the land, which is not to be violated. … Besides, the remainder, after such enclosure, would not be as good to the rest of the commoners, as the whole was when they could all make use of the whole; whereas in the beginning and first peopling of the great common of the world, it was quite otherwise. (Ch. 5, sec. 35)

It is not that Locke thinks the remaining land is better used when held in common than when held privately. Quite the contrary. Just a few paragraphs later, he asserts that one acre of enclosed land is as productive as ten or even a hundred held in common (Ch. 5, Sec. 37). Still, once the scarcity constraint is reached, if any part of the commons that remains is to be privatized, that must happen by the consent of all the tenants in common. 

But what rules should govern their giving of consent, and if the land is to continue to be held in common, how should it be managed?

Locke on government

One possible rule would be to handle everything through private negotiation. That could be done through contracts under which each of the remaining common owners agrees to cede their claims to any newly enclosed parcel in exchange for compensation from its owners. If the value of the land really increases through enclosure, it should theoretically be possible to obtain that consent. 

Such an approach could well be practicable if the number of parties is relatively small and could lead to privatization of more of the land than the rule of first-use would allow. Even then, however, some common property would remain, either because agreement on further enclosures could not be reached or because the nature of the property in question made actual enclosure impossible.

Once private negotiations had run their course, the remaining common property, and any further enclosures, could be managed by a committee of the whole, under a rule of unanimous consent. However, that is not what Locke recommends. Instead, he recommends establishment of a government empowered to devise the new set of rules for the protection of property that has been privatized through first use and for management of any remaining commons. 

Locke, after all, was not an anarchist. He believed that it was not only legitimate but prudent for free individuals to pursue their mutual interests by joining together under a common government. But the kind of government Locke supported would be limited in important ways.

First, its principal purpose – in fact, its only purpose – would be protection of property: “Government has no other end but the preservation of property” (Ch. 7, Sec. 94). “The great and chief end, therefore, of men’s uniting into commonwealths, and putting themselves under government, is the preservation of their property” (Ch. 9, Sec. 124). (Importantly, under the principle of self-ownership, “property” for Locke included not just the lands and homes of the landed rich, but the personal security and livelihoods of everyone.)

Second, Locke prescribed what would later come to be called a liberal government. Such a government would be characterized by the separation of executive and legislative powers. It would also follow the rule of law, that is, of “settled standing rules, indifferent, and the same to all parties” (Ch. 7, Sec. 87). To ensure just enforcement of the law, no one should be the judge in their own case. 

Third, recognizing that it would be impracticable to secure the actual consent of every citizen for every decision, Locke understood that the ordinary business of government should be conducted by majority rule. Even so, the actions of government should command at least the tacit support of all citizens ( Ch. 8, Sec. 199-120). By tacit consent, Locke meant that anyone who accepts the benefits of living under a government, whether those benefits take the form of protection of property or simply the use of public highways, must assent to be governed by all the laws of that government without picking and choosing. 

Locke’s justification for the establishment of such a government is largely pragmatic. He recognized that government involved a tradeoff between the freedoms of the state of nature and the benefits of a more settled way of living:

For being now in a new state, wherein  he is to enjoy many conveniencies, from the  labour, assistance, and society of others in the same community, as well as protection from its whole strength; he is to part also with as much of his natural liberty, in providing for himself, as the good, prosperity, and safety of the society shall require; which is not only necessary, but just, since the other members of the society do the like. (Ch. 9, Sec. 130)

Such, then, are Locke’s views regarding property and government. If we take them seriously, what do they tell us about the issues we face today?

Implications for climate policy

Figure 1 shows emissions and concentrations of carbon dioxide in the earth’s atmosphere since the beginning of the Industrial Revolution ( The relationship between the two lines in the chart reflects the fact that emissions of carbon dioxide, the most important greenhouse gas (GHG), stay in the atmosphere for a long time – 300 to 1,000 years (NASA). I will organize the following discussion of climate policy around four stylized stages of development, based loosely on the figure. The exact data and historical dates are less important than the more general economic and environmental relationships. 

  • Stage 0: Any anthropogenic GHG emissions are so low as to be undetectable against the background of natural processes. They are absorbed by natural sinks and do not cause any cumulative rise in GHG concentrations in the atmosphere. 
  • Stage 1: The rate of GHG emissions exceeds the absorptive capacity of natural sinks. Ongoing emissions cause atmospheric concentrations to rise, but concentrations remain too low to cause any significant harm.
  • Stage 2: GHG concentrations reach a level that begins to cause nontrivial harm to sensitive populations who are particularly exposed to sea-level rise, droughts, storms, or other climate effects. However, during this stage, the aggregate benefits of emission-causing activities exceed the harms at the margin.
  • Stage 3: GHG concentrations reach the point that the aggregate harms caused by further anthropogenic emissions significantly exceed the benefits.

Stage 0 is strictly hypothetical. If there ever was such a stage, it presumably ended before Figure 1 begins. Some research suggests that emissions from early farming and deforestation began to cause measurable anthropogenic effects thousands of years ago. Whether that is so or not, Stage 1 appears to have gotten well underway early in the Industrial Revolution, with the first large-scale use of coal as a fuel. For the sake of discussion, we can think of Stage 2 as having started sometime in the nineteenth or early twentieth century, and Stage 3 sometime more recently. 

I realize that some readers may insist that we have not yet reached Stage 3, so we don’t have to do anything yet, but I would invite them to stay with the discussion. One reason is that, as Adler makes clear, is that the harms done by anthropogenic climate change require redress already during Stage 2, when they do not yet exceed benefits such as low waste-disposal costs or the availability of cheap fossil fuels. Furthermore, it seems to me that even those libertarians who are most skeptical of climate science should be prepared, arguendo, to give some thought to the kind of policy response they would endorse if and when Stage 3 did arrive.

The stages are briefly described in Table 1, along with names for the transitions from each stage to the next.

Let’s turn now to a discussion of how, under Lockean principles, human impacts on the climate should be managed as we move through the stages. 

Stage 1. We will begin here, since Stage 0 is of no real economic interest. If there ever was such a stage, the waste disposal capacity of the atmosphere would not have been a scarce good; anyone could use as much as they wanted with no effect on anyone else.

Things get interesting only when the scarcity threshold is passed and greenhouse gas concentrations begin to rise. Because CO2 persists in the atmosphere for centuries, each newly emitted ton uses up part of the remaining capacity of the atmosphere to absorb the gas without harm. For that reason, any first-use appropriation of emission rights would be like the enclosure of a portion of a common field – a fixed-quantity appropriation. In contrast, a first-use claim to draw water from a river would allow withdrawals year after year at a given rate – a fixed-rate appropriation.

The difference between fixed-quantity and fixed-rate appropriations seems to have been missed by libertarians who rely on Murray Rothbard’s analysis of air pollution. According to Rothbard, “If a factory owned by A polluted originally unused property, up to a certain amount of pollutant X, then A can be said to have homesteaded a pollution easement of a certain degree and type.” (Rothbard, 1982, p. 146.)

The context makes it clear that he is thinking of a fixed-rate appropriation, which would allow A to continue to emit X pollution year after year. However, Rothbard was writing about less persistent forms of air pollution like smoke or the emissions that cause acid rain. A CO2 easement, in contrast, would have to be of the fixed-quantity variety, giving the right to emit a certain number of tons of CO2 or equivalent. A perpetual fixed-rate easement of any finite size would eventually exhaust the capacity of the atmosphere to absorb wastes harmlessly.* But even if homesteading were limited to fixed-quantity easements, GHG concentrations would, over time, reach a point beyond which any additional emissions began to cause harm. At that point, Stage 2 would begin.

Stage 2. As soon as Stage 2 begins, two things happen. First, there is a change not just in the magnitude of the effect of one person’s GHG emissions on others, but also in the kind of effect. Luc Bovens points out the difference in a paper on grandfathering of emission rights (Bovens, 2011, p. 14). In Stage 1, emissions by one person adversely affect others only to the extent that they reduce the remaining waste disposal capacity of the air, thereby using up potential opportunities for others to emit the same kinds of greenhouse gasses in the future. Beyond that point, further emissions would violate Locke’s third duty, the duty not to engross. In contrast, once Stage 2 gets underway, any emissions begin to cause direct harms in the form of flooding, crop damage, extreme weather, and other climate-related phenomena. Those harms are different in kind from the benefits of low-cost waste disposal to emitters. Those further emissions violate the first two of Locke’s duties rather than the third.

Second, once emissions begin to harm others directly, even if the harm to the persons and property of pollution victims is (by assumption) less than the benefit to polluters, there can be no further first-use claims to emission rights. All of the fixed-quantity rights that are legitimately homesteaded during Stage 1 will have been, or will soon be, used up. At that point, the whole earth will be in the position that Locke described for the England of his day, in which “no one can inclose or appropriate any part, without the consent of all his fellow-commoners.”

Importantly, though, obtaining such consent for further emissions should still be possible, since the benefits of further emissions exceed the costs. What is required is for the government, in its role as protector of property and manager of the remaining commons, to develop appropriate rules to facilitate the process.

For GHG emissions, rules to facilitate private negotiation are not likely to be enough. Such emissions are not comparable to, say, local particulate pollution from an iron smelter. Even if such a local polluter could no longer renew a fixed easement, it might be possible to negotiate a compensation agreement with victims. But, given that the harms done by GHG emissions are spread worldwide, private negotiations would be impracticable.

Fortunately, Lockean principles do not require that everything be done by private negotiation. The government could step in to set administrative or market-oriented rules. We will have more to say about various alternative rules later, but whatever the details, as long as the government operated under appropriate liberal safeguards, including rules that are fixed and are the same for all, its actions would be consistent with Lockean principles.**

If everything went well, emissions could continue to increase under the Stage 2 rules until they reached the cost-benefit threshold that marks the beginning of Stage 3. Beyond that point, it would not be worthwhile for polluters to pay enough to compensate victims, so emissions would fall toward net zero. Atmospheric concentrations would stabilize, and eventually, with long lags for some effects like sea-level rise, the climate would stabilize, too.

Stage 3. Unfortunately, it appears that things have not developed according to this happy scenario. High transaction costs have stymied private deal-making. Courts have failed to block unjustified emissions. The government has not balanced the interests of winners and losers in a fair and efficient manner. Also, to some extent, emissions have grown beyond the cost-benefit threshold simply because not enough people (or not the right ones) realized what was happening until it was too late. As a result, at least according to the conventional view of matters, we are already deep into Stage 3. What next?

The key difference between Stage 3 and Stage 2 is that the harm done by any additional emissions now exceeds the benefits. To return from where we are to the cost-benefit threshold, let alone to the threshold of harm, will require substantial reductions in total emissions. Doing so raises many questions, including which sources should make the reductions, how fast the process should proceed, and what policy instruments should be used to reach emission targets. What help with the answers, if any, can Locke provide?

Consider, first, the question of which sources should reduce emissions. One view is that existing sources should be protected, or “grandfathered,” when emission quotas are set. If so, those sources would be allowed to continue polluting unless and until they are bought out with cash payments, or subsidies for installation of emission-reducing technologies, or in some other way. However, I see major problems with the grandfathering of emission rights for greenhouse gasses. 

One problem, already mentioned, is that any first-use easements homesteaded during Stage 1 would have been for fixed quantities only, not for perpetual emissions at a fixed rate. As such they would long since have been used up. The same goes for any emission rights granted by negotiation or by government action during Stage 2.

Leigh Raymond (2014) raises a different issue that further weakens the argument for grandfathering. According to Raymond, Locke’s argument in favor of acquisition by first use is strongest when applied to appropriations that are both tangible and beneficial. The classic example would be building a fence to enclose a small portion of a large common pasture. The fence is tangible, and the act of enclosure is beneficial, in that it incentivizes pasture improvements and disincentivizes overgrazing. Locke himself, we remember, considered enclosed land to be 10 or more times as productive as unimproved commons.

In contrast, an emission easement established by homesteading is neither tangible nor beneficial. An easement removes a part of the airshed from the commons legally, but not functionally. The easement fails the functional test because there is no fence or other barrier to prevent emissions, and whatever harm they cause spreads over the whole planet. Meanwhile, the owner of the easement gains the advantage of low-cost waste disposal while others suffer the costs of climate change. The imbalance between private benefits and public costs means that the airshed will continue to be used just as inefficiently as before the easement was claimed. Emissions are likely to continue far beyond the point where costs exceed benefits.

Taking all of this into account, little remains of the case for favoring current sources when setting targets for reductions of emissions. At most, some temporary grandfathering might be allowed to give industry and commerce sufficient time to adjust smoothly or to build a coalition in support of a new emissions-management regime. But I can find nothing in Locke that points to a natural right for polluters to continue to do harm after they have done more than enough already.

The Lockean case for carbon pricing

We cannot find all the answers to climate policy in the pages of Locke’s Second Treatise. There are many practical issues for which his principles provide little guidance. Those include setting optimal target levels for GHG emissions and concentrations, determining the speed with which they should be achieved, striking a balance between mitigation and adaptation, and others. But there is one final area on which Locke’s views do have a bearing. 

We have argued that homesteading of pollution easements fails Raymond’s tangible-and-beneficial test because it removes the polluted portions of the airshed from the commons in legal terms, but not functionally. But what if it were somehow possible to remove emission rights from the commons functionally, but not legally? That could be done by putting a price on GHG emission. In that case, the requirement to pay for each unit of pollution would act as a functional deterrent for emissions even while the atmosphere itself remained a global commons in legal terms.

One way to do that would be with a cap-and-trade approach. The government would carry out its duty to protect people and their property from the harms of climate change by auctioning off a specified number of marketable permits, each allowing a fixed quantity of emissions. In effect, it would be leasing a part of the community’s common airshed to private parties while retaining legal ownership.

Functionally, holders of the permits would treat them like private property. They could use the permits themselves to lower their waste-disposal costs or they could resell them to others who valued them more highly. The buyers might even include conservation organizations who would buy permits to hold them unused. 

Alternatively, the government could impose a fee or tax per ton of CO2-equivalent. The result would be very much the same, both legally and functionally, as a cap-and-trade system. The only real difference would be the terms on which the government leased out emission rights. Instead of auctioning off a predetermined quantity of pollution rights, and allowing the market to set the price, the government would set the price and allow the market to determine the quantity.

Either version of emission pricing would at least partially meet Raymond’s criterion of tangibility. Although the physical airshed would remain unenclosed, the permits themselves would be discrete, scarce, and tradeable. Either version would meet the criterion of benefit by ensuring that certificates ended up in the hands of those who value them most, and either would incentivize both consumers and producers to adopt clean technologies.

Furthermore, the proceeds of a permit auction or pollution fee could be used to compensate the victims of climate change for harm done to their persons and property. That could be done either directly, by distributing cash, or indirectly, by lowering taxes that people would otherwise have to pay to maintain the government with its police, courts, and other institutions of property protection. 

Readers may object that if emissions pricing were implemented during Stage 3, the proceeds of permit sales or pollution fees would, by assumption, be insufficient to compensate for the harm done. That is true. Yes, it would have been better to establish a pricing regime during Stage 2 – one with parameters tight enough to ensure that we would never reach Stage 3. But that did not happen.

But even if, as consensus thinking has it, we are already deep into Stage 3, emission pricing is still attractive. Although the goal is now not just to roll back the rate of emissions, but also the concentrations of GHGs in the atmosphere, there are limits on how fast this should happen. Too ambitious a program could disrupt supplies of investment goods needed for clean energy, carbon capture, and seawall construction. It could lead to overinvestment in existing, imperfect, abatement technologies without giving time to develop more effective alternatives. A pricing scheme would allow the flexibility needed to balance the speed of achieving any given emission target against the cost of doing so, and could complement other forms of regulation and public investment.

What we have learned

In conclusion, what have we learned from our close examination of Locke’s views of property and government? What are their implications for climate policy? Here is a summary:

1. Locke puts property at the center of his political theory. He starts with self-ownership, a concept that is the basis of what we call “human rights” in the modern world. He extends ownership to the products of labor and to land appropriated from the commons by first use. Rights to property are matched by corresponding duties not to harm others or their property, and to leave enough for others when taking from the commons.

2. Locke sees protection of property, including protection of the freedoms and human rights implied by self-ownership, as the central purpose of government. But not just any government will do. A legitimate government must conform to the principles that later came to be known as liberalism, including majority rule, separation of powers, and rule of law.

3. Locke freely mixes deontic and consequentialist arguments in support of his views on property and government. He defends the institution of property as a natural right, but also points to the superior productivity of private, as opposed to common, ownership. He sees government as a pragmatic compromise in which people give up a part of the absolute freedoms that they enjoy in the state of nature, receiving enhanced security and prosperity in return.

4. Locke’s views on the duty not to harm and the government’s role in protecting persons and property include no exceptions for harms resulting from air pollution, climate change, or any other kind of environmental externality.

5. Locke’s views on appropriation by first use provide polluters with little or no defense. Rothbard (1982) interprets Locke in a way that entitles uncontested polluters to have “homesteaded an easement” to a certain rate of pollution. Perhaps in preindustrial times, polluting the air might legitimately have been compared to taking a drink from an abundantly flowing stream. In the modern world, however, the binding constraint on polluters is not Locke’s duty to leave “as much and as good” for others, but rather, the duty not to cause harm to others and their property. As Adler points out, that constraint comes into play as soon as anthropogenic climate change first begins to cause harm to others, even if those harms do not yet exceed aggregate benefits. 

6. The resource at issue in climate change is the ability of the earth’s atmosphere to absorb greenhouse gases. That resource cannot be physically partitioned, so it remains an unenclosed commons. Once legitimate first-use claims have been exhausted, Locke assigns the duty of managing any remaining unenclosed commons to the government. Price-based management mechanisms would be fully consistent with Locke’s thinking. The bottom line: Neither the deontic nor the consequentialist side of Locke’s reasoning supports the laissez-faire approach to climate change favored by many libertarians. If we take Locke seriously, there is a clear role for government in the productive management of our global climate commons – one that can and should be exercised in a way consistent with the principles of liberal government.

*Writing elsewhere, Rothbard (1998, p. 244) rejected the Lockean proviso against engrossment, saying that “if latecomers are worse off, well then that is their proper assumption of risk in this free and uncertain world.” However, even rejection of the proviso would only permit a finite increase in the number of fixed-quantity easements that polluters were allowed to claim by first use. It would still not allow perpetual fixed-rate easements.

**This assumes that there is just one government in the world. Multiple national governments would complicate the process, requiring international negotiations and international compensation payments. Bovens (2011) discusses those issues, but they lie beyond the scope of this commentary.

Photo Credit: Godfrey Kneller, Public domain, via Wikimedia Commons