Figure Credit: Climate Analytics
Coal is by far the largest emitter of carbon dioxide per pound of fuel when it comes to fossil fuels. Therefore, rapidly phasing out coal is an essential part of keeping the global temperature from rising over 1.5℃. As the image shows, global pledges and fossil fuel investments will miss the 1.5℃ threshold by 1.8℃. Coal is used to produce almost 30% of power worldwide with the largest emitters being the United States using coal for over 30% of its power supply, the EU using coal for 19% of its power, and China using coal for over 57% of its power. In order to keep warming below the 1.5℃ threshold by 2100 the world must be completely divested from coal by the year 2050 - a major goal of the Paris Climate Agreement. At the COP 23 there is a lot of open discussion between governmental parties and nongovernmental organizations (NGOs) like Climate Analytics on how countries can divest from coal most efficiently (although I have not heard of nor seen any United States party members discussing coal - or fossil fuel - divestment).
The founder and CEO of Climate Analytics Bill Hare gave a talk generally about global coal consumption and the Paris Agreement. The global community is far behind in both divesting in coal as well as shutting down coal power plants (again displayed by the figure in blue). First, shutting down coal power plants is the most direct way to divest the coal industry. However, because the power plants are run by companies that are typically owned by multinational companies or investment banks an abrupt coal factory shutdown would severely hurt the international companies and banks - thus, damaging the global economy. The best path towards reaching our zero coal production by 2050 to avoid the 1.5℃ threshold (green area in the figure) is widely believed to be a carbon fee. Essentially, a carbon fee would facilitate private industry coal divestment while simultaneously encouraging private reinvestment into renewable energies - opposed to renewable energies being developed by the government. Furthermore, the US taxpayer also pays a carbon fee for how much carbon they emit every year, however, that money is returned to them at the end of the year if they emit less carbon than the average US citizen - incentivising a low carbon lifestyle. Finally, funds left over in the carbon fund after go towards retraining coal workers and helping pay for elder coal workers early retirement.
The idea of a price on carbon would obviously be set by individual countries, but if every country in the Paris Agreement pledged to implement a carbon fee then 1) global coal divestment would rapidly accelerate (because coal emits the most CO2 per amount of fuel), and 2) greenhouse gas emissions would plummet.
Here is Bill Nye talking about his vision of a Carbon Fee: https://www.youtube.com/watch?v=CwrJtO8s-L0