This essay, as mentioned in the title, refers to the 3 major conferences held in the past two decades, organised by the United Nations. The main objective was to reduce emissions, save the environment from further damage, and increase sustainability
The first one to be held was the Rio Summit, also known as the United Conference on Environment and Development (UNCED). Following the Stockholm Conference of 1972, the UNCED received a far greater attendance, it received the participation of 172 countries with 108 heads of state, also included numerous non-governmental organisations (NGOs), in the order of 2,400 and 17,000 people in the NGO forum. The outcome of this conference was three major agreements aimed at changing our approach towards development.  These were: Agenda 21, a comprehensive document that lists the actions that must be taken where humans directly affect the environment. The Rio Declaration on Environment and Development (RDED), a list of 27 principles ‘defining the rights and responsibilities of the states’ towards sustaining the environment. Finally, The Statement of Forest Principles (SFP), a non-legally binding document that makes several recommendations towards the preservation of forest areas. 
Agenda 21 is divided into 4 sections. The first deals not with the environment but rather problems concerned with society, such as poverty and health. The second deals with development and the resources needed to develop such as biodiversity, and atmospheric pollution. The third again deals raising awareness to the general public about sustainability and increase the participation from their part, especially through NGOs and businesses. Lastly the fourth deals with the methods of implementation of the previous three. 
As with the SFP, the RDED is not a set of international laws, but rather they are guidelines as to how the individual states should act towards protecting the environment. These include principles like the ‘polluters pay’ in which those who excessively pollute the environment should pay for their damage.  The SFP main concerns are to control the deforestation of forests through chemicals and logging. 
In 1997 the second major conference was held, this time in Kyoto, Japan. This conference resulted in the formation of the Kyoto Protocol, which is linked to the United Nations Framework Convention on Climate Change (UNFCCC), a treaty created at the UNCED in Rio. The difference between the conference and the protocol is that the protocol is essentially a law and so all the signatories must commit to it. One of the main objectives of this protocol was to reduce by five per cent against 1990 levels the greenhouse gases emissions of the most industrialised countries in the world over the five-year period 2008-2012. Hence this protocol is relatively new considering that the conference was over a decade ago. The protocol did not enter into force until 2005, and the full details of the rules to implement it...