The reasons that renewables are, at present, needing some kind of protection or support are:

• The commercial 'playing field' is tilted against them:
  

• In a report published in 2004, the New Economics Foundation made a conservative estimate that worldwide subsidies for fossil fuels amounted to about $235bn a year—and there seems not to have been much change since then. 
• The continued existence of subsidies for oil, gas and coal, is confirmed by recent reports that the G20 intend to remove them (see, for example, G20 fossil fuel subsidy push may aid climate talks).
• Nuclear power is heavily subsidised as described in Nuclear Subsidies.
• There is still no global cap on emissions and schemes such as the EU ETS are not working properly. For those kinds of reasons, the price of CO₂ emissions is far too low.

• It is widely accepted that several renewable sources of power need support until their cost-reduction curves have levelled off and they a properly established. When any particular renewable technology is well established and, when there is a level playing field for renewables, then there may be a case for withdrawing support for that particular technology (more below). 

More generally, the Stern report said that climate change is the greatest market failure the world has seen, and that various actions will be needed to compensate for that failure.

Rather that piling subsidy upon subsidy, we should be aiming to wind down the arms race of subsidies, reserving them for where they are really needed:

• Ensure that a proper price is paid for CO₂ emissions (more below).
  
• Remove all subsidies from oil, gas and coal, as the G20 say they will do. There may be a case for providing support for carbon-capture and storage (CCS) until it is established.
  
• Remove subsidies from nuclear power following procedures outlined in Section 4 of the Nuclear Subsidies report.
• Retain support for renewables that have not yet reached the bottom of their cost-reduction curves or where there are special reasons for providing support. Regarding the latter point, if, for example, the majority of people feel that onshore wind farms spoil the landscape (and that is by no means clear) there may be a case for providing a subsidy to cover the extra cost of putting wind turbines out at sea.
  
• Remove support from renewable sources of power that have reached the bottom of their cost-reduction curves and are well established. 

In raising the price of CO₂ emissions, it is important to ensure that emissions from the nuclear cycle are properly accounted for. In her book "Nuclear power is not the answer", Helen Caldicott says "The use of nuclear power causes, at the end of the road and under the most favourable conditions, approximately one-third as much carbon dioxide (CO₂) emission as gas-fired electricity production." But this is only with the highest grades of ore. The use of poorer ores as a source of fuel for nuclear reactors "would produce more CO₂ emissions than burning fossil fuels directly." In other words, "nuclear reactors are best understood as complicated, expensive, and inefficient gas burners." (p. 6).

Raising the price of CO₂ emissions may be of some help to nuclear power but it would be even more helpful to renewables. With the changes outlined above, it is unlikely that nuclear power would be commercially viable.