The U.N. Could Have a Secret Legal Weapon to Fight Climate Change

Long a matter of political disputes, how to address climate change is increasingly becoming a legal question. Most recently, on March 29, the United Nations General Assembly voted to seek a legal opinion from the International Court of Justice (ICJ) on the matter. To date, international law has offered those facing the greatest hardships from climate change few legal tools to sue polluters or receive funds to help adapt to threatening weather changes. An obscure U.N. treaty from the 1970s could potentially change all that.

The recent U.N. resolution was put forward by the Pacific island nation of Vanuatu and co-sponsored by more than 130 countries. Vanuatu is seeking compensation from the states most responsible for climate change for increasingly powerful cyclones that have struck the low-lying archipelago in recent years.

The U.N. resolution asks the ICJ, sometimes called the World Court, to issue an advisory opinion on states’ obligations “in respect of climate change.” Unlike the International Criminal Court, which investigates alleged crimes by individuals, the ICJ is a civil tribunal that adjudicates disputes between countries. It is the primary judicial agency mentioned in the U.N. founding charter.

The ICJ’s advisory opinions are not legally binding, but they carry legal authority and moral weight. Legal experts point out that such opinions can affect domestic courts’ judgments and provide guidance on questions of definitions, scope, or jurisdiction for international tribunals or panels, such as investor-state arbitration or trade panels at the World Trade Organization (WTO).

As climate change intensifies, activists, scholars, nongovernmental organizations, and small island states are eager for a legal strategy through which they can seek compensation for loss and damage. The obvious starting point is the U.N. Framework Convention on Climate Change (UNFCCC), the centerpiece of the global efforts to address climate change and the organizing framework for more detailed agreements such as the 2015 Paris accords. But the UNFCCC states that any convention disputes must be settled by negotiation unless countries have committed to ICJ jurisdiction. Only two—Cuba and the Netherlands—have done so.

A little-known U.N. agreement about climate disputes could provide the ICJ jurisdiction over a much larger set of countries. In effect since 1978, the Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques, known as EnMod, affirms that state parties are “not to engage in military or any other hostile use of environmental modification techniques having widespread, long-lasting or severe effects as the means of destruction, damage or injury to any other State Party.” EnMod defines environmental modification as “the deliberate manipulation of natural processes—the dynamics, composition or structure of the Earth, including its biota, lithosphere, hydrosphere and atmosphere, or of outer space.” Weather events explicitly fall within the purview of EnMod.

To be clear: EnMod was not designed for climate change as we understand it in the 21st century. The treaty was intended to prevent countries from, for example, weaponizing rain clouds to hurt another country’s agriculture (as the United States allegedly attempted against Cuba during the Cold War). And an EnMod challenge, even within its intended framework, has never been tested at the ICJ.

Even so, legal history is replete with examples of laws and policies having unintended consequences. When the WTO was created in 1995, for instance, Washington insisted that it have a strong and legalistic dispute settlement process because U.S. officials expected the United States would win most of its cases. But the United States has frequently lost at the WTO. In each case, Washington has had to either change its policies or face higher tariffs on some exports.

EnMod’s 78 state parties comprise 70 percent of global population and have been responsible for 83 percent of carbon dioxide emissions since the onset of the treaty, based on our calculations using data from the 2022 Global Carbon Budget. Its membership includes states recognized as being major contributors to climate change—such as the United States, China, and most of Europe—as well as states self-identifying as suffering climate change damages—such as Bangladesh, Vietnam, Afghanistan, and Ghana. This gives the convention a legal standing that is qualitatively different from most or all climate change agreements. The 1997 Kyoto Protocol and the 2015 Paris accords included no legal enforcement mechanisms beyond what is stipulated in the UNFCCC.

Though all EnMod member nations continue to emit greenhouse gases, some have made very deliberate efforts to curtail them. The United Kingdom, for example, has now decreased its emissions substantially below the 1990 emissions benchmark set by the Kyoto Protocol. According to our calculations, the U.K. and Canada are each responsible for about 2 percent of cumulative global emissions since 1978, but the U.K. cut its emissions by 42 percent from 1990 to 2022, while Canada increased its emissions by 19 percent over the same period. Canada’s lack of progress on emissions reductions might make it a more promising target for political and legal action by vulnerable states.

While EnMod’s text does not mention the ICJ specifically, it does state that consultation and cooperation should be handled “within the framework of the United Nations and in accordance with its Charter” and, crucially, that the “international procedures may include the services of appropriate international organizations.” As the primary judicial agency of the U.N., the ICJ would seem to qualify. Still, the treaty’s failure to explicitly designate a legal venue for resolving EnMod-related disputes means its jurisdiction remains uncertain.

Vulnerable countries seeking compensation for loss and damage, referred to as applicants, should choose their legal targets carefully. (Vanuatu is not currently a member of EnMod, so it could not use it for a legal challenge unless it joins.) The likely targets, known as respondents, would be countries that ratified EnMod and have done relatively little to lower emissions in the decades since. Canada, Australia, and the United States might be politically appealing respondents; even China, although not wealthy on a per capita basis, could come under scrutiny.

Applicants would need to establish “military or any other hostile use” of environmental modification techniques by a target country. The argument that major emitters are causing climate change for military purposes is not likely to get far because militaries are responsible for a tiny fraction of total global emissions. Climate change also doesn’t serve an obvious military purpose, such as allowing one country to conquer another.

Still, applicants could contend that continued emissions in the face of authoritative scientific evidence of climate change is tantamount to intentionally, or at least recklessly, imposing “destruction, damage or injury” on other EnMod members. This rationale is strengthened by the fact that alternative energy sources are increasingly available at commercially viable costs in the global north. In this sense, Canada has been more reckless with its emissions than the U.K.

EnMod guarantees members the right to use “environmental modification techniques for peaceful purposes.” Most emissions come from civilian, not military, sources, and a respondent might argue that greenhouse gases were emitted for the peaceful purpose of economic production. But applicants could respond that while economic production itself might have a peaceful purpose, the environmental modification caused by emissions does not. On the contrary: Climate change is expected to be enormously destructive and harmful to all forms of life on Earth. The scientific community is increasingly able to attribute extreme climate events, such as cyclones or wildfires, to climate change.

The recent U.N. resolution opens the door to providing greater clarity over whether EnMod, and even the ICJ itself, could be used for climate lawsuits. The ICJ is expected to spend the next year analyzing the relevant international law and issuing an advisory opinion. The court should include the EnMod treaty within the scope of its analysis.

Even if the advisory opinion’s authors ultimately decide that EnMod does not provide the ICJ jurisdiction over climate litigation—or do not address the topic—the treaty gives state parties some political leverage they could use in the future. EnMod members still have the right to lodge a complaint with the U.N. Security Council, which has the legal authority to investigate the complaint or refer it to the ICJ.

This tactic could be useful to groups such as the Climate Vulnerable Forum of 58 countries disproportionately affected by the consequences of climate change. Its professed interest in discussing loss and damage is likely to mean that novel legal and political climate compensation strategies will emerge over the coming decade. Developing these can—and should—include revisiting and potentially repurposing arcane U.N. treaties such as EnMod.