The electricity sector has tended to be one of the first industries to face technology change motivated by sustainability concerns. Whilst efficient market designs for electricity have tended to focus upon market power concerns, environmental externalities pose extra challenges for efficient solutions. Thus, we show that ad hoc remedies for market power alongside administered carbon prices are inefficient unless they are integrated. Accordingly, we develop an incentive-based market clearing design that can include externalities as well as market power mitigation. A feature of the solution is that it copes with incomplete information of the system operator regarding generation costs. It is uses a network representation of the power system and the proposed incentive mechanism holds even with energy limited technologies having temporal constraints, e.g., storage. The shortcomings of price caps to mitigate market power, in the context of sustainability externalities, are overcome under the proposed incentive mechanism.