Estimation of the opportunity cost is necessary for the economic assessment of environmental conservation policies. This paper considers the case where an environmental good is negatively affected in the process of the production of marketable goods. In the presence of externalities, conservation implies the undertaking of abatement measures by polluters. A relevant measure of opportunity cost in these settings is the abatement cost required to preserve or restore a unit of the environmental good in question. Current economic literature lacks an established methodology for deriving such measures, as it commonly focuses on pricing pollutants rather than the natural stocks affected by them. This paper uses a non-optimal valuation approach suggested by Fenichel and Abbott (2014) as a point of departure and develops a framework for deriving the opportunity cost of conservation as the cost of externality abatement per unit of environmental good. An empirical illustration is provided for the case of the farmed and wild salmon trade-off in Norway in light of the current pollution control regulations.

When ecosystem services value estimates are applied in the economic assessment of environmental policies, high accuracy of these estimates is required. One of the directions in the scientific discussion on biases in stated preference (SP) valuation surveys builds on dual-process theories of judgment. The paper contributes to this literature by presenting an experiment where two types of judgment were induced via separate versus joint valuation of environmental goods. The results demonstrated that policy relevance of environmental issues, e.g., the need for conservation measures, increases emotional response, causing a larger bias in the separate design as it involves "valuation by feeling". This finding suggests that the context of a specific policy, which is often the reason for conducting SP surveys, influences the answers, thereby making the results less reliable for use in cost-benefit analysis.