Tackling climate change can be achieved through local and regional initiatives, such as the Covenant of Mayors, which create energy and climate plans with mitigation measures. Upon the development of energy plans, the mitigation of greenhouse gas emissions (GHG) can be achieved through an individual or joint approach. The research aims to upgrade methods for local and regional energy planning through the choice of mitigation actions and alternative scenarios for the reduction of GHG emissions. This is achieved through optimisation of the selection of mitigation measures in the case of the wider Dubrovnik area in Croatia by choosing the most suitable option for implementation when comparing individual and joint approaches for the planning of the measures. Moreover, the implementation of single and sets of mitigation measures is compared through the total cost abatement curve. The modelled problem represents a non-linear problem as exponential functions and multiplication of variables occurs in the modelled equations. Visualisation of the results is achieved via the total cost abatement curve which ranks measures from the most cost-effective to the least cost-effective. It is shown that with the use of optimisation models, it is possible to find such sets of measures and alternative scenarios, which will, with less financial means, reach a minimal reduction of CO2 emissions by 40% in local and regional energy systems and result in financial savings of three times in the analysed case. In this way, it could be possible to increase the overall implementation of SECAP measures and mitigate the problem of the lack of appropriate financial planning.