Solar, wind and hydro technologies convert enthalpy into entropy and would cool the Earth, except that it is in dynamic radiative balance with the Sun, which has a relatively infinite energy supply and would restore the equilibrium. The enthalpy has to be restored from the Sun because the enthalpy cannot be replaced, except from higher temperatures by the Second Law of Thermodynamics, ultimately by the temperature of the Sun. There would be additional warming of the Earth to maintain its temperatures, causing global warming. Therefore renewable energy would not reduce global warming. The theory that reducing fossil fuel combustion would reduce warming by carbon dioxide could be tested, as I have described in my Proposal to Demonstrate Greenhouse Warming see martinknox.com  and my book Animal Farm 2 available on Amazon.