Climate change is an important issue both for society and for companies which invest in long term projects. However, climate change futures are inherently uncertain, and this raises important questions about how companies should take account of such climate effects and uncertainties in choosing investment projects. In some circumstances voluntary emissions reductions, that is reductions in emissions not directly mandated by predictable financial returns, can be privately beneficial for the firm on a net basis, in addition to generating broader social benefits not directly captured by the firm. This thesis develops methods by which firms can include these future climate effects and uncertainties into capital budgeting and investment appraisal, and uses these methods to explore the conditions in which voluntary emissions reductions might provide net benefits to firms