Changing international relations at the end of the 20th century, as well as concern for how various countries would handle sensitive environmental issues, led to the UN Conference on Environment and Development, also known as the Rio Conference. Held in June 1992, the conference produced the first major treaty in response to global climate change. Called the UN Framework Convention on Climate Change (UNFCCC) [PDF], the legally non-binding treaty did not set greenhouse gas emissions standards on individual countries. Rather, the treaty illustrated a framework for negotiating future specific international treaties that could set specific greenhouse gas limits.

The UNFCCC required all nations that were party to the convention, which included most industrialized nations but not private sector parties, to participate in meetings called “Conference of the Parties” (COP). At the initial COP, held in Berlin, Germany in 1995, the nations confirmed that they must determine “quantifiable emissions limitations and reduction objectives.” At a later COP, held in Kyoto, Japan in 1997, the nations established the Kyoto Protocol [PDF].

Participating nations negotiated [PDF] three main issues during the COP in Kyoto. First, participating nations targeted reductions for six specific greenhouse gases: carbon dioxide, methane, nitrous oxide, sulphur hexafluoride, hydrofluorocarbons and perfluorocarbons. Each industrialized nation would be required to reduce emissions of these gases to a specific percentage of a baseline level (under the Kyoto Protocol, the baseline level were emissions of those gases in the year 1990). For example, the US was required to reduce emissions by 7% below 1990 levels.

Second, developing countries were not held to emissions limitations or reductions, although it was anticipated that developing countries would later face quantitative limitations. Finally, countries were permitted to transfer emission reduction units between themselves, but were not permitted to rely wholly on trades to reach their target emission levels.

Additional COPs, including ones held in Buenos Aires, Argentina in 1998, The Hague, Netherlands in 2000 and Marrakech, Morocco in 2001 arranged terms for some of the treaty’s finer points (including potential credit for carbon “sinks” in the form of forests and agricultural lands and consequences for failure to meet emissions targets).

The US, along with 191 other states, signed the treaty. The Kyoto Protocol faced intense scrutiny in the US Senate. Ultimately, the Senate declined to ratify the treaty, and the Bush Administration reaffirmed that stance in 2001. By not ratifying the treaty, the US chose not to be bound by the Kyoto Protocol. The first commitment period to the Kyoto Protocol concluded in 2012. While the EU and several other countries agreed to join a second Kyoto Protocol commitment period running until 2020, the UN has championed the development of a new international climate change treaty. A COP, planned for 2015 in Paris, France, will outline a new agreement with legal force.

US President Barack Obama, already concerned with potential pushback from the Senate regarding ratification of the to-be-developed treaty, is interested in pursuing a climate change “accord.” Such a document would not require Senate ratification, but would rest on political will and social approval.