The analysis of ecosystem services (ES) is becoming a key-factor to implement policies on sustainable technologies. Accordingly, life cycle impact assessment (LCIA) methods are more and more oriented toward the development of harmonized characterization models to address impacts on ES. However, such efforts are relatively recent and have not reached full consensus yet. We investigate here on the transdisciplinary pillars related to the modeling of LCIA on ES by conducting a critical review and comparison of the state-of-the-art in both LCIA and ES domains. We observe that current LCIA practices to assess impacts on "ES provision" suffer from incompleteness in modeling the cause-effect chains; the multifunctionality of ecosystems is omitted; and the "flow" nature of ES is not considered. Furthermore, ES modeling in LCIA is limited by its static calculation framework, and the valuation of ES also experiences some limitations. The conceptualization of land use (changes) as the main impact driver on ES, and the corresponding approaches to retrieve characterization factors, eventually embody several methodological shortcomings, such as the lack of time-dependency and interrelationships between elements in the cause-effect chains. We conclude that future LCIA modeling of ES could benefit from the harmonization with existing integrated multiscale dynamic integrated approaches.

In the Dasgupta-Heal-Solow-Stiglitz model of capital accumulation and resource depletion we show the following equivalence: If an efficient path has constant (gross and net of population growth) savings rates, then population growth must be quasi-arithmetic and the path is a maximin or a classical utilitarian optimum. Conversely, if a path is optimal according to maximin or classical utilitarianism (with constant elasticity of marginal utility) under quasiarithmetic population growth, then the (gross and net of population growth) savings rates converge asymptotically to constants. JEL Code: Q10, Q32.

The relatively new and still amorphous concept of "Green Growth" can be understood as a call for balancing longer-term investments in sustaining environmental wealth with nearer-term income growth to reduce poverty. We draw on a large body of economic theory available for providing insights on such balancing of income growth and environmental sustainability. We show that there is no a priori assurance of substantial positive spillovers from environmental policies to income growth, or for a monotonic transition to a "green steady state" along an optimal path. The greenness of an optimal growth path can depend heavily on initial conditions, with a variety of different adjustments occurring concurrently along an optimal path. Factor-augmenting technical change targeting at offsetting resource depletion is critical to sustaining long-term growth within natural limits on the availability of natural resources and environmental services.

The Green Paradox states that, in the absence of an appropriate tax on CO2 emissions, subsidizing a renewable backstop such as solar or wind energy brings forward the date at which fossil fuels become exhausted and consequently global warming is aggravated. We shed light on this issue by solving a model of depletion of non-renewable fossil fuels followed by a switch to a clean renewable backstop, paying attention to timing of the switch and the amount of fossil fuels remaining unexploited. We show that the Green Paradox occurs if the backstop is relatively expensive and full exhaustion of fossil fuels is optimal, but does not occur if the backstop is sufficiently cheap relative to the cost of extracting the last drop of fossil fuels plus marginal global warming damages as then it is attractive to leave fossil fuels unexploited and thus limit CO2 emissions. We show that, without a carbon tax, subsidizing (taxing) the backstop might enhance social welfare if fossil fuel reserves are not fully (fully) exhausted. We also discuss the potential for limit pricing when the non-renewable resource is owned by a monopolist. Finally, we show that if backstop are already used and there is a new sequence of backstops becoming economically viable as the price of fossil fuels rises, a lower cost of the backstop will either postpone fossil fuel exhaustion or leave more fossil fuel in situ, thus boosting green welfare. However, if a market economy does not internalize global warming externalities and renewables have not kicked in yet, full exhaustion of fossil fuels will occur in finite time and a backstop subsidy always curbs green welfare.