Montreal Protocol (1987)
It is an international treaty designed to protect the ozone layer by phasing out the production of a number of substances believe to be responsible for ozone depletion. Forty-six countries joined the treaty, which was originally signed in 1987. The Montreal Protocol demanded that developed nations should accept a series of stepped limits on the main five CFCs (chlorofluorocarbons) use and production. One of them was to reduce the use and production of CFCs in 50% of their 1986 baseline until 1999.

IPCC (1988)
The Intergovernmental Panel on Climate Change (IPCC) was established to assess the scientific, technical and socio-economic information relevant for the understanding of human induced climate change, its potential impacts and options for mitigation and adaptation. It is a scientific intergovernmental body set up by the World Meteorological Organization (WMO) and by the United Nations Environment Program (UNEP).
 
Eco 92 (1992)
It was a major conference held in Rio in 1992, attended by many world leaders who discussed the environment. The idea of sustainable development was introduced: The UN sought to help Governments rethink economic development and find ways to halt the destruction of irreplaceable natural resources and pollution of the planet.
 
Kyoto Protocol (1997)
The treaty was negotiated in Kyoto, Japan, in 1997, opened for signature 1998, and closed in1999. The agreement came into force in 2005. The Kyoto Protocol commits industrialized countries to reduce their collective emissions of greenhouse gases by 5.2% compared to the year 1990 until the year 2012.

Status of the Kyoto Protocol
Besides establishing different, specified gas emissions levels for each country, the Kyoto Protocol was responsible for many discussions. Among various experts, scientists and critics there is some debate about the usefulness of the protocol, and there have been cost-benefit studies performed on its usefulness. The concept of the certified reduction (carbon credits came) into existence as a result of this debate. Two mechanisms must be mentioned:
 

• The European Union Emission Trading Scheme (EU ETS): It is the largest multi-national, greenhouse gas emission trading in the world and a main pillar of the European Union climate policy. All the members of the European Union have to reduce greenhouse gas emissions to levels specified for each of them between 2002 and 2007 (as well as the emission reduction from 2008 to 2012 stated by the Kyoto Protocol). The Protocol agreed “caps” or quotas on the maximum amount of Greenhouse gases that each participating country from this group can produce. Countries that have not used up their quotas can sell their unused allowances as carbon credits, while businesses that are about to exceed their quotas can buy the extra allowances as credits, privately or on the open market. This is called EUA – European Union Allowance. These quotas will be revisited in 2008, characterizing the second phase of this market. These countries can buy a percentage of their quota in CERs (Certified Emission Reductions), but this percentage is limited, aiming to stimulate Europe’s emission reduction.
  
 
• Certified Emission Reduction (CER): Kyoto Protocol stated that the developed countries that signed the Protocol, referred to as Annex I countries, are obliged to reduce GHG emission and must submit an annual greenhouse gas inventory. On the other hand, the developing countries that signed the Protocol, referred to as Non-Annex I countries, have no GHG emission reduction obligations but may participate in the Clean Development Mechanism. The developing countries receive incentives. These incentives are characterized by greenhouse gases emission reduction projects. This reduction is measured in tons of CO2 and changed into credits. Governmental entities and the UN must approve the credit through the projects. Periodic certifications in the project must be held by independent entities.