Normally, analyzing the details of climate change negotiations is not part of the core topics of this blog.
However, exceptions exist, and further to the COP21 climate deal of December 2015, such an exception really does seem appropriate, in order to outline a quick summary.
Indeed, this agreement was signed in December by a large majority of countries, representing more than 90% of current carbon emissions. The COP21 deal is a legally binding international treaty, even though it does not contain any explicit sanctions for those who fail to meet their objectives.
These national objectives are called "Intended Nationally Determined Contribution" (INDC) and frequently look out until 2030 (a summary can be found here, detailed INDCs of 161 countries can be found here). Studies show that the outcome of these INDCs in terms of annual CO2 emissions can differ, depending on how you interpret the INDCs and how you modelize the world of the future (see comparison of studies in the graph below).
However, none of these mentioned studies come to the conclusion that the current INDCs would be sufficient to limit global warming to a maximum of +2°C :
While the INDCs submitted 2015 only allow for a mere stabilization of current emission levels (at around 50 Gt CO2 per year, see first graph above), a rather quick reduction of emission levels, to 40 Gt CO2 by 2030, would actually be needed, according to an official UNEP study:
This shows that the COP21 agreement is a compromise of various interests. The question will now be as to if/how it will be implemented, if/how to organize the mentioned additional effort, and which costs are implicated.