International climate policy is based on the UNFCCC –– the UN Framework Convention on Climate Change produced at the Rio Earth Summit in 1992. The express goal of the Framework Convention is to reduce GHG emissions to prevent “dangerous anthropogenic interference with the climate system.” (One of the fundamental problems with the Framework Convention is defining exactly what “dangerous anthropogenic interference with the climate system” is.)
The Framework Convention is a policy and therefore does not have the force of law. Although it does require GHG inventories, it sets no mandatory GHG limits. It contains no enforcement mechanisms. It does provide for protocols, which are treaties that, if ratified, would become international law and would set emissions limits and determine enforcement mechanisms. The Framework Convention requires an annual Conference of Parties (COP), which is an international meeting of all the signatories of the Framework Convention, aimed at developing protocols. The best known is the Kyoto Protocol.
The 1997 COP in Kyoto, Japan introduced the Kyoto Protocol. To enter into force, it required not less than 55 percent of all Framework Convention signatories to ratify it and for those ratifying countries to account for at least 55 percent of total GHG emissions. It entered into force in 2005 when Russia ratified the protocol. Once ratified, the 36 developed countries and former Soviet republics and satellite states (called collectively the Annex I countries) must reduce their GHG emissions by a collective five percent below 1990 emissions levels by 2012. Some countries must reduce their emissions more because of their high emissions totals and overall wealth; for example, if the U.S. were to ratify the protocol, it would have to reduce its emissions by seven percent. Presently, all but two Framework Convention member states have ratified the Kyoto Protocol: the U.S., which does not intend to ratify it, and Afghanistan, which has expressed no opinion on ratification. COPs still meet in November or December each year (they're gathering in Bonn, Germany right now actually!).
The Paris Agreement - just about the time when the world was questionining whether the UNFCCC process had failed and needed to be scrapped, the world was able to come together and adopt the Paris Agreement in 2015. This landmark achievement represents the first truly global step forward in both acknowledging and addressing climate change on a planetary scale. Rather than being prescriptive, the agreement allows individual countries to determine their own contributions toward emissions reductions with an overall goal of limiting warming this century to less than 2 degrees Celsius. It further encourages efforts to limt that warming to 1.5 degrees Celsius. For the US, one of the keystones of achieving our nationally determined contributions to the Paris Agreement was set to be the Clean Power Plan. However, when the Trump Administration came to power in January 2017, they quickly began to work to not only scrap the Clean Power Plan, but also to begin the process of withdrawing the US from the Paris Climate Agreement, suggesting that it was unfairly hard on US industry interests. The rest of the world remains committed to the Paris Agreement, though. And, because the process by which a country withdraws takes 4 years, the soonest the US will be officially withdrawn is November 2020, and depending on the political climate of the country, it is entirely possible the process will not be fully executed.