# Corpsia--A Feasible Second Best Solution?
## 5 Conclusions  
In this paper, we show that carbon offsetting, even under well established program standards, can barely support its promise of climate neutral growth in aviation. This finding is based on a systematic review of carbon offset characteristics with regard to climate and regulatory integrity and an empirical analysis of the registry data of the most important offset standards under CORSIA. These findings have implications for policy. Based on carbon offsets, CORSIA was launched to ensure climate-neutral growth in international flights from 2021 onwards. Thus, airlines need to compensate every additional ton above the 2019 baseline with one equivalent ton released by carbon offset projects. The eligibility criteria established by the ICAO Council specify the requirements for offsets that can be used, currently resulting in six eligible offset program standards. CORSIA's climate-neutral growth aspiration would require every offset to mirror net carbon reduction. Many offsets eligible under CORSIA cannot guarantee this, facing the three major challenges of additionality (carbon reductions would not have occurred without the offset project), non-leakage (carbon reduction somewhere does not increase carbon emissions somewhere else), and permanency (today's reduction might be released tomorrow). Ensuring maximum climate integrity under CORSIA would dramatically reduce the carbon offset supply and increase transaction costs. This stems from the fact that while all eligible offset programs offer projects with high integrity, most of their offset supply is generated in large-scale projects considered to have low integrity, such as renewable energy projects. However, CORSIA's financial attractiveness is based on these offsets. Another critical characteristic of eligible carbon offsets are adverse effects. Program standards have considerably improved their regulatory integrity by implementing safeguard clauses which take effects on the local community into account. However, while direct effects on the local community, such as social oppression, can be reduced by monitoring compliance with safeguard clauses, indirect effects such as crowding out are more difficult to observe. If airlines are not only interested in profit maximization, it would be interesting to know whether higher prices indicate higher offset integrity for them. On the contrary, if airlines are profit maximizers and favor the cheapest offsets, it would be important to know whether this would support offsets with minor climate impact. Our results show that offset prices cannot be used as a signal to maximize climate integrity. Projects with higher offset prices do not guarantee a higher likelihood of additionality. To ensure the maximum climate and regulatory integrity of CORSIA, policy makers should consider prioritizing carbon reduction projects that are relatively small, aiming at energy efficiency at the consumer level and selected carbon storage projects. Positive examples exists among established climate programs. In the case of small energy-efficient projects, several climate programs have focused on such projects, including the WorldBank's Pilot Auction Facility for Methane and Climate Change Mitigation and the Norwegian purchase program. However, the current supply of such offsets is extremely low and does not meet CORSIA's demand [60]. Furthermore, it is unclear whether there is enough potential supply. Thus, we emphasize the importance of natural carbon storage under high standards despite its own major weaknesses in order to achieve urgent large-scale carbon reductions and mitigate climate change. Taken together, our results reveal carbon offsetting as a weak second best solution to achieving carbon neutral growth, which should be considered as transitional. This is in line with the findings of the 2022 IPCC report arguing that CORSIA will not sufficiently decrease aviation carbon emissions in order to be consistent with the temperature goals of the Paris agreement [61].