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January 05, 2021 Article 1

International Environmental Law

International treaties and principles protect the environment and guard against climate change

by David Hunter

Profound environmental changes caused by the increasing scale of human activity have led many observers to conclude that the planet has entered the “Anthropocene”—a geologic era signified by human impact on the biosphere. International environmental law is the set of agreements and principles that reflect the world's collective effort to manage our transition to the Anthropocene by  resolving our most serious environmental problems, including climate change, ozone depletion and mass extinction of wildlife. More generally, international environmental law aims to achieve sustainable development—i.e., development that allows people to have a high quality of life today without sacrificing the quality of life of future generations. International environmental law is thus critical both for addressing specific environmental threats and for integrating long-term environmental protection into the global economy.

But not all environmental threats trigger international (as opposed to solely national or local) response. For countries to sacrifice their autonomy, some advantage must be gained in addressing the problem collectively. Typically, countries turn to international cooperation where (l) the environmental impacts are transboundary (such as pollution into the Great Lakes) or global (such as climate change); (2) some international activity contributes to environmental harm, for example, the international trade in elephant ivory or the killing of whales; or (3) international coordination of financial or technical support can catalyze action (for example, for the global conservation of biological diversity). In these circumstances, international cooperation—whether in the form of a binding treaty or a non-binding “soft law” agreement—is necessary for an effective response to the environmental challenge.

Throughout most of the last century, international environmental law primarily reflected bilateral or regional disputes over shared resources, such as rivers or lakes that cut across national boundaries. These disputes led to diplomatic tensions that either resulted in an international legal case or were settled through relatively narrow regional or bilateral treaties. The most famous and important of these disputes was the Trail Smelter Arbitration, where Canada was held responsible for air pollution entering the United States.
In recent years, bilateral disputes involving for example Slovakia’s proposed construction of a dam on the Danube River near Hungary, Uruguay’s authorization of two pulp mills that threatened to pollute Argentina, and Australia’s challenge of Japanese whaling operations, highlight the importance of international law in peacefully resolving environmental conflicts between countries.  Such disputes are resolved at the International Court of Justice, the UN Law of the Sea Tribunal or other international tribunals.

In addition to the peaceful resolution of environmental conflicts, international environmental law also is relied on to balance the planet’s ecological limits with the world’s ever-growing economy to prevent irreversible environmental harm in the first place. Today, governments regularly meet to address the general sustainability of the planet or to negotiate one of the literally hundreds of bilateral, regional and global treaties aimed at managing a specific environmental challenge before it’s too late.

Sustainable Development Summits

The United Nations first convened countries to address the global environment at the 1972 UN Conference on the Human Environment in Stockholm.  The Stockholm conference highlighted the international aspects of emerging environmental challenges and legitimized the environment as an area for international cooperation.  The Stockholm conference also created the United Nations Environment Programme (UNEP)— an institutional home for environmental protection in the United Nations. Headquartered in Nairobi, Kenya, UNEP continues today to be a leading catalyst for global environmental cooperation.

Since the 1972 Stockholm Conference, the world has met regularly in a series of major summits aimed at shifting the world generally toward a path of sustainability.  The most important by far has been the 1992 UN Conference on Environment and Development (UNCED), also known as the Rio "Earth Summit.'  Virtually every world leader attended the Earth Summit, where they  agreed to three major treaties (addressing climate change, biological diversity and desertification), and a 500-page blueprint for sustainable development (known as Agenda 21).  Most importantly, Rio marked the formal acceptance of sustainable development as the goal of a modern economy and of international environmental law. Indeed, since Rio the concept of sustainable development has received nearly universal acceptance among every sector of international society.

Sustainable development was also the organizing framework for major environment and development summits in Johannesburg in 2002 and Rio again in 2012 (the Rio+20 Summit).  These summits are big affairs, attended not only by governments but also by thousands of civil society and private sector representatives.  Reflecting this wider audience, the recent UN-sponsored Summits have promoted public-private Partnerships for Sustainable Development and more recently led to adoption of the Sustainable Development Goals (SDGs).  These non-binding goals serve as a strategic plan for coordinating the global community toward achieving concrete, measurable goals by  2030.

International Environmental Principles

At both Stockholm in 1972 and at Rio in 1992, the countries adopted a set of basic principles (see, e.g., the Rio Declaration on Environment and Development). Some of these principles are emerging as customary law, helping to resolve environmental disputes and guide negotiations of the various environmental treaties.  Ten of the most important environmental principles are briefly defined in the sidebar box on page --.

Global Environmental Agreements

Since the 1972 Stockholm Conference, countries have embarked on an ambitious schedule of international environmental treaty negotiations.  Today, these treaties form the core of international environmental law. They can be grouped into treaties aimed at: (1) protecting the global atmosphere, including preventing climate change and ozone depletion; (2) conserving wildlife and biological diversity; (3) managing the oceans and marine environment; and (4) regulating global movement of chemicals, wastes and other hazardous substances (see table of Global Environmental Agreements).

Representative Global Environmental Agreements

Number of State Parties

 Opened for Signature

Entered into Force

 Global Atmosphere




Montreal Protocol




 UN Framework Convention on Climate Change




  Kyoto Protocol




Paris Agreement




Wildlife and Biodiversity




Convention on Biological Diversity




Cartagena Protocol on Biosafety




Convention on International Trade in Endangered Species (CITES)




Convention on Migratory Species




Convention to Combat Desertification




Ramsar  Wetlands Convention




UNESCO World Heritage Convention








  Law of the Sea Convention




 Straddling Fish Stocks Agreement








Basel Convention on Hazardous Wastes




  Stockholm Convention on POPs




  Rotterdam Convention on PIC




  Minimata Convention on Mercury

128 signed (30)



Addressing climate change

At least since the 1980s, scientists have warned that increasing concentrations of carbon dioxide and other greenhouse gases would warm the earth's atmosphere and change our climate. Today, climate change is the most serious environmental challenge of our time, and we are already seeing its impacts: increased global temperatures; melting glaciers; reduced Arctic sea ice; increased tidal and storm surges; and increased heat waves and droughts.
Avoiding the most dangerous impacts from climate change has been a major focus of international environment law since the 1992 United Nations Framework Convention on Climate Change (the UNFCCC), which recognized climate change as "a common concern of humankind" and set out a framework for global action to avoid harmful impacts. The Convention set an informal goal to reduce emission levels of greenhouse gases to 1990 levels by the year 2000, but it did not impose any binding targets or timetables on any country.
Thirty- eight industrialized countries subsequently agreed in the 1997 Kyoto Protocol to reduce their overall emissions to approximately 5 percent below 1990 levels by the year 2012. Having agreed to cap emissions, the countries also established elaborate procedures for trading the rights to pollute under the cap. The Kyoto Protocol's "cap-and-trade" approach thus envisioned a global market for reducing carbon dioxide and other greenhouse oases. The United States first signed the Protocol in 1998 but rejected it three years later after President Bush took office. The Kyoto Protocol would catalyze Europe’s reduction in GHG emissions and create a market for GHG emission credits--but the departure of the United States from the Protocol and the need to include China and other major emitting countries would lead to a search for a different approach.  That approach would (finally) come in the form of the 2015 Paris Agreement on Climate Change.

The Paris Agreement, which sits within the framework established by the 1992 UNFCCC, significantly advanced the world’s effort to address climate change.  For the first time, all countries, including the two largest emitters (China and the United States), pledged to take serious—if not binding— commitments. The governments endorsed a specific global average temperature goal— of “well below” 2°C increase over pre-industrial levels —as the temperature that would give the world a reasonable chance of avoiding the worst climate impacts.  The Parties also signaled that if necessary they will “pursue efforts” to limit the temperature increase to 1.5 °C.

Most significantly, the Paris Agreement signaled a long-term shift from fossil fuels as Parties agreed to reach a “global peaking” of GHG emissions “as soon as possible” and “to undertake rapid reductions thereafter” to achieve a balance between  net GHG emissions and removals in the “second half of this century.    Achieving this post-2050 goal  does not necessarily require the elimination of fossil fuels, because efforts could also increase GHG removals from the atmosphere, for example by growing more trees or by developing effective carbon capture technology.  The Agreement nonetheless builds momentum for drastically lower dependence on fossil fuels and provides a clear market signal for long-term investments in alternative energy sources. 

Having set long-term shared goals, the Paris Agreement deemphasized the cap-and-trade approach of prior negotiations in favor of a “pledge-and-review” approach, relying primarily on each country’s commitment or  “nationally determined contribution” (NDC) to reduce climate change. By the end of the Paris negotiations, 186 countries would announce an NDC. The United States, for example, agreed to reduce by 2020 its overall GHG emissions 26-28% from 2005 levels, and China  agreed among other things to peak their emissions and improve  their GHG efficiency by 60-65% by 2030.  Each party’s implementation of their pledge would be subject to some form of monitoring, reporting and verification. 

The primary weakness of the Paris Agreement’s approach is that an “ambition gap” exists between the countries’ cumulative pledges and what is scientifically necessary to avoid the worst climate impacts.  Indeed, current commitments are estimated to allow an increase in global average temperatures somewhere between 2.5 and 3.7 °C, well above safe levels.  The parties acknowledged the need for reviewing their NDCs every five years, beginning in 2020.  Successive commitments are supposed to build on previous commitments, taking into account each country’s particular circumstances.

The Paris Agreement not only aimed at reducing GHG emissions but also at maintaining forests, improving land-use, expanding financial and technical resources  for developing countries, supporting adaptation to unavoidable climate change impacts and compensating those who suffer loss and damage from climate change.  Both in the large number of countries making commitments and of issues addressed, the Paris Agreement was most comprehensive effort yet to address climate change.  Nonetheless, the Trump Administration has renounced Paris Agreement, leaving the United States once again isolated globally with respect to fighting climate change.
Climate change currently dominates all other environmental issues, but other multilateral environmental agreements address other critical environmental challenges.

Reversing ozone depletion

Beginning in the late 1970s scientists warned that certain widely used chemicals could be depleting the earth’s protective stratospheric ozone layer. In response, countries first negotiated the 1985 Vienna Convention for the Protection of the Ozone Layer and two years later the Montreal Protocol on Substances that Deplete the Ozone Layer. The Montreal Protocol has subsequently been revised or amended every two or three years, resulting in a comprehensive phase out of most chlorofluorocarbons (CFCs), and other ozone depleting substances. Nearly every country in the world has joined the Montreal Protocol and the use of ozone-depleting substances has plummeted, And the ozone layer is slowly recovering.  Recently, the Parties to the Montreal Protocol have extended it to phase out certain related chemicals that contribute to climate change.

Conserving nature

The planet is facing a sixth great wave of extinctions and a general decline in wildlife and natural habitats.  The leading global treaties for conserving nature are the Convention on Biological Diversity, the Convention on International Trade in Endangered species (CITES) and the Convention on Migratory Species. The 1992cBiodiversity Convention has the general goal of conserving the planet's biological diversity. The Convention sets an international framework to support domestic conservation efforts and includes binding protocols on managing genetically modified organisms (GMOs) and ensuring that local communities share the benefits from biodiversity conservation. CITES establishes binding controls on international trade in parts of rare species of animals and plants. For example, CITES prohibits all commercial trade in elephant ivory, tiger pelts, rhinoceros horns, and thousands of other plants and animals. The Convention on Migratory Species (CMS) provides a framework for countries to protect the entire life cycle of threatened migratory species.  The CMS includes separate annexes tailored to the needs of specific animals or groups of animals (for example migratory bats). Other nature conservation treaties protect internationally important wetlands, natural heritage sites, and certain species such as whales, sea turtles or migratory birds. 

Protecting the marine environment

The UN Convention on the Law of the Sea sets forth rules for managing the oceans, including marine conservation.  Under the regime, coastal states are responsible for protecting the marine environment within 200 miles of their coasts, and flag states (i.e., the countries that license a particular vessel) are responsible for controlling their ship’s activities in the high seas beyond 200 miles. More specific treaties limit marine pollution from ships and regulate fishing for highly mobile fish species that straddle territorial waters and the high seas.

Regulating chemicals and wastes

The global management of chemicals is organized around a non-binding Strategic Agreement for Integrated Chemicals Management and four global treaties that regulate hazardous chemicals and wastes. The Rotterdam Prior Informed Consent Convention requires that chemical exporters ensure that receiving countries have given their prior, informed consent. Importing governments can then manage the environmental and public health risks inherent to hazardous chemicals. The Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and their Disposal imposes similar consent requirements for shipments of hazardous wastes and requires the environmentally sound management of such wastes. The Stockholm Convention on Persistent Organic Pollutants prohibits or significantly restricts the production and use of some of the world's most environmentally harmful chemicals, including dioxins, PCBs, and DDT. More recently, the Minimata Mercury Convention has curbed the multiple pathways of global mercury pollution.

International environmental law has successfully addressed many serious issues. Many harmful chemicals are now controlled, the ozone layer is recovering, and populations of important wildlife species, including whales and sea turtles, are increasing because of international environmental agreements. But many other indicators of global environmental quality, such as declining fish stocks, increasing temperatures and increasing forest loss, (such as . . can you briefly list a few more?) have deteriorated in the decades since the Stockholm conference. Perhaps most urgently, today we face growing evidence that human-made environmental change will cause profound global impacts if not addressed. International environmental law is but one (albeit necessary) tool to successfully face these new challenges.  But the strong record of international environmental cooperation from Stockholm to Paris provides hope for the future.

For Further Reading
Bodansky, Daniel, The Art and Craft of International Environmental Law, Harvard University Press, 2009.
Hunter, David, et al. International Environmental Law and Policy. Foundation Press, 2013.
Birnie, Patricia, and Alan Boyle. International Law and the Environment. 3rd ed. Oxford University Press, 2009.


Principles of International Environmental Law

State Sovereignty. Countries have the sovereignty to exploit their own resources pursuant to their own environmental and developmental policies.

Common Concern. The global environment is a common concern of humanity,

Duty Not to Cause Environmental Harm. Countries have the responsibility to ensure that activities within their jurisdiction or control do not cause damage to the environment of other countries or of areas beyond the limits of national jurisdiction.

Common but Differentiated Responsibilities. In view of their different contributions to global environmental degradation, countries have common but differentiated responsibilities.

The Polluter Pays Principle. Countries should promote the Internalization of environmental costs, reflecting the approach that the polluter should bear the cost of environmental harm.

Environmental Impact Assessment. Environmental impact assessment shall be conducted for proposed activities that are likely to have a significant adverse impact on the environment.

The Precautionary Principle. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation.

Public Participation. Environmental issues are best handled with the participation of all concerned citizens.

Notification and Consultation. Countries shall provide prior and timely notification to, and consult with, potentially affected countries on activities that may have a significant adverse transboundary environmental effect.

Peaceful Resolution of Disputes. Countries shall resolve all of their environmental disputes peacefully.

David Hunter (dhunter@wcl, is Professor of Law at the American University Washington College of Law. He is Director of the Program on Environmental and Energy Law and co-author of International Environmental Law and Policy (Foundation Press, 2013).