We study the Baltic Sea countries' declaration to reduce nutrient loads by
50% in each country in an ecological-economic model. The model consists of
country-based abatement-cost functions, and transfer coefficients describin
g how phosphorus and nitrogen flow from one country to another, as estimate
d in a hydrological model of the Baltic Sea. We show that for nitrogen in p
articular the overall abatement costs of the current policy are much higher
and that the benefits are more uneven than under a cost-efficient policy.
Consequently, one can expect that countries with high marginal abatement co
sts have the least incentives to follow the agreement and to invest in nitr
ogen abatement. This is also confirmed by our data. Therefore, we suggest a
nd outline a joint implementation policy to promote cost efficiency and to
increase incentives for investments.