What if we tap sources of energy, like fusion and to some extent(*) fission, which are novel to the normal solar/earth system and release extra heat energy into

What if we tap sources of energy, like fusion and to some extent(*) fission, which are novel to the normal solar/earth system and release extra heat energy into the atmosphere? Since this study is obviously only relevant in the far future, why not add in likely future technologies to the mix? It seems to me that at some point we could just wrap the earth in shutters(since we're talking far future anyway) or intentionally release greenhouse gasses to servo the planet's temp. * - I believe much of the geothermal heat is actually heat from fission already so I don't know if fission energy changes the balance much.