The "Big Three" The MEAs on climate change (UNFCCC), Biodiversity (UNCBD) and desertification (UNCCD) are collectively called the "Big Three" agreements or the "Rio Conventions"

MEAs are international legal instruments that have a goal of addressing global environmental problems and environmental protection; are concluded between countries and international organizations as "parties," and is governed by international law protocols under the UN umbrella.

The Stockholm Conference on the Human Development (1972) was one of the first attempt to address inter-relationships between environment and development at the global level . It also adopted the first global action plan for environment.

The Earth Summit (1992) held in Rio de Janeiro accelerated the development of modern MEAs - more than 60% of existing MEAs were adopted after the Summit (including the "Big Three" conventions on climate change, biodiversity and desertification). It also urged national governments to redirect national and international policies towards integration of environmental, economic and development objectives (and therefore towards sustainable development).

Some of the core MEAs have a global significance clustered around the themes of biodiversity, atmosphere, land, chemicals and hazardous wastes, regional seas etc.

MEAs can be of two types: (1) legally-binding agreements and set commitments in form of legally-binding targets and time-tables, or (2) non-binding instruments that set out important issues and priorities, foster discussion and attention, and stimulate new thinking and development of legally-binding instruments Implementation of an MEA is a process of converting international commitments and requirements at the global level into laws and policies at the national levels in order to induce behavioral change of target groups, i.e. those actors causing the problem in question. Thus "compliance" is a key undertaking in an MEA, referring to whether the countries adhere to the agreement provisions and undertake implementation measures, including procedural measures (e.g. national reporting).

Global leaders meeting in Paris in December 2015 to adopt the "Paris Agreement" on climate change.

How are MEAs developed? Global environmental problems and initial ideas that are widely shared among countries are usually the starting points for MEAs. One or more of such countries organises a conference to allow expression of common interest and formulate recommendations texts.

Such internationalefforts identify the core elements of an MEA and establish a process for the implementation of the convention. A series of negotiations among countries results in convention text agreed upon and opened for other countries to join (or "ratify") the MEA. An MEA is usually named after the city where it was agrred to and signed (for example "Paris Agreement"). MEAs are also supported by scientists and NGOs working together.

A typical MEA has a number of institutional arrangements such as a Conference of Parties (COP) which is the ultimate decision-making body on implementation and development of the MEA. A Secretariat supports COP and performs a number of varied functions depending on the mandate of the MEA, and includes a number of Executive and subsidiary bodies that provide scientific, technical, or financial advice to the COP. MEAs may also include clearinghouses to facilitate exchange of information, financial mechanisms, etc.

MEAs have a number of strengths and weaknesses

Weaknesses include, for example, lack of synergies among MEAs, inadequate implementation and coordination of MEAs at the national level, inadequate compliance and enforcement, lack of environmental and performance indicators to measure the effectiveness of MEAs, or inadequate funding for selected MEAs.

Strengths of MEAs include, for example, growing commitment from international bodies and national governments to explore synergies, clarity in who has to do what, or increased attention to principles of precaution and prevention.