Abstract.A reliable and up-to-date ship emission inventory is essential for atmospheric scientists quantifying the impact of shipping and for policy makers implementing regulations and incentives for emission reduction.

The Arctic sea-ice is retreating faster than predicted by climate models and could become ice free during summer this century. The reduced sea-ice extent may effectively "unlock" the Arctic Ocean to increased human activities such as transit shipping and expanded oil and gas production. Travel time between Europe and the north Pacific Region can be reduced by up to 50 % with low sea-ice levels and the use of this route could increase substantially as the sea-ice retreats. Oil and gas activities already occur in the Arctic region and given the large undiscovered petroleum resources increased activity could be expected with reduced sea-ice. We use a bottom-up shipping model and a detailed global energy market model to construct emission inventories of Arctic shipping and petroleum activities in 2030 and 2050 given estimated sea-ice extents. The emission inventories are on a 1×1 degree grid and cover both short-lived components (SO₂, NO_x, CO, NMVOC, BC, OC) and the long-lived greenhouse gases (CO₂, CH₄, N₂O). We find rapid growth in transit shipping due to increased profitability with the shorter transit times compensating for increased costs in traversing areas of sea-ice. Oil and gas production remains relatively stable leading to reduced emissions from emission factor improvements. The location of oil and gas production moves into locations requiring more ship transport relative to pipeline transport, leading to rapid emissions growth from oil and gas transport via ship. Our emission inventories for the Arctic region will be used as input into chemical transport, radiative transfer, and climate models to quantify the role of Arctic activities in climate change compared to similar emissions occurring outside of the Arctic region

International shipping is a significant contributor to Global Greenhouse Gas (GHG) emissions, responsible for approximately 3% of global CO 2 emissions. The International Maritime Organization is currently working to establish GHG regulations for international shipping and a cost effectiveness approach has been suggested to determine the required emission reductions from shipping. To achieve emission reductions in a cost effective manner, this study has assessed the cost and reduction potential for present and future abatement measures based on new and unpublished data. The model used captures the world fleet up to 2030, and the analysis includes 25 separate measures. A new integrated modelling approach has been used combining fleet projections with activity-based CO 2 emission modelling and projected development of measures for CO 2 emission reduction. The world fleet projections up to 2030 are constructed using a fleet growth model that takes into account assumed ship type specific scrapping and new building rates. A baseline trajectory for CO 2 emission is then established. The reduction potential from the baseline trajectory and the associated marginal cost levels are calculated for 25 different emission reduction measures. The results are given as marginal abatement cost curves, and as future cost scenarios for reduction of world fleet CO 2 emissions. The results show that a scenario in which CO 2 emissions are reduced by 33% from baseline in 2030 is achievable at a marginal cost of USD 0 per tonne reduced. At this cost level, emission in 2010 can be reduced by 19% and by 24% in 2020. A scenario with 49% reduction from baseline in 2030 can be achieved at a marginal cost of USD 100 per tonne (27% in 2010 and 35% in 2020). Furthermore, it is evident that further increasing the cost level beyond USD 100 per tonne yield very little in terms of further emission reduction. The results also indicate that stabilising fleet emissions at current levels is obtainable at moderate costs, compensating for fleet growth up to 2030. However, significant reductions beyond current levels seem difficult to achieve. Marginal abatement costs for the major ship types are also calculated, and the results are shown to be relatively homogenous for all major ship types. The presented data and methodology could be very useful for assisting the industry and policymakers in selecting cost effective solutions for reducing GHG emissions from the world fleet.

International shipping is a significant contributor to global greenhouse gas (GHG) emissions, and is under mounting pressure to contribute to overall GHG emission reductions. There is an ongoing debate regarding how much the sector could be expected to reduce emissions and how the reduction could be achieved. This paper details a methodology for assessing the cost-effectiveness of technical and operational measures for reducing CO 2 emissions from shipping, through the development of an evaluation parameter called the Cost of Averting a Tonne of CO 2 -eq Heating, CATCH, and decision criterion, against which the evaluation parameter should be evaluated. The methodology is in line with the Intergovernmental Panel on Climate Change (IPCC) and with regulatory work on safety and environmental protection issues at the International Maritime Organization (IMO).The results of this study suggest that CATCH 550 $/tonne of CO 2 -eq should be used as a decision criterion for investment in emission reduction measures for shipping. In total, 13 specific measures for reducing CO 2 emissions have been analysed for two selected case ships to illustrate the methodology. Results from this work shows that several measures are cost effective according to the proposed criterion. The results suggest that cost effective reductions for the fleet may well be in the order of 30% for technical measures, and above 50% when including speed reductions. The results of this study show that the cost effectiveness approach for the regulation of shipping emissions is viable and should be pursued in the ongoing regulatory process.

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