Background to COP21, Paris, December 2015

The 21st 'Conference of Parties' since 1992 [COP21] is poised to deliver agreement on the rules providing for periodic review of the 'Intended Nationally Determined Contributions' to greenhouse gas emissions. 146 of the 195 countries in the UN 'Framework Convention on Climate Change' [UNFCC] had submitted proposals by 1 October 2015, 155 by 30 October.
The 'worst case' scenario based on the current trajectory of emissions [which many scientists believe to be the 'most likely' scenario] would result in global warming of 4.5 to 6°C  by 2100.  The 'intended contributions' published by 1 October have been estimated [by the UNFCC] to result in global warming of 2.7 to 3.0°C by 2100.  These contributions are intended to be achieved by 2025 to 2030.  To achieve the widely recognised objective of global warming less than 2°C by 2100 [or 1.5°C as some countries demand] is expected to need more ambitious contributions than those currently on offer.  Hence the importance of COP21, one outcome of which is expected to be an agreed  mechanism for periodic review of intended contributions to greenhouse gas emissions reduction.
Source: http://www.cop21.gouv.fr/en/2c-target-result-of-state-contributions/