One necessary step to limit global warming is to phase out fossil fuel production, which can deprive the value of foreign investments and amount to breaches of investment treaties. Normally investment treaties are silent about the standards of compensation where treaty violations are established, and tribunals mostly refer to the “full reparation” standard under general international law, which can result in a massive amount of compensation and impose a heavy burden on States taking climate actions. Based on existing investment arbitration practices, the amount of awarded damage under the “full reparation” standard can be reduced on the grounds of unviability of fossil fuel projects, contributory negligence of investors, international environmental obligations and principles, and depressed energy price in the peak demand era. To ensure the consideration of these grounds in the calculation of damages, an interpretation document is needed to clarify the meaning of the “full reparation” standard.