Climate change is quickly becoming a survival concern because it brings multiple challenges globally (GoP, 2021b). Since about 1750, the observed rise in Greenhouse Gases (GHGs) is clearly due to anthropogenic activities (IPCC, 2021). The burning of fossil fuels due to anthropogenic activities including transportation is one of the main causes of the increase in CO₂ emissions (IPCC, 2014; Notte et al., 2018; Hussain et al., 2020). Over the last century, international sea transportation has been the primary means of transit (Halim et al., 2018) accounting for 80–90% of global trade (Chang, 2012; Chu-Van et al., 2019; MERSIN et al., 2019; Yang and Ma, 2019; Zhou et al., 2020; Al-Enazi et al., 2021). Maritime vessels are directly involved in climate change by releasing the substances of global warming because of the utilization of fossil fuels (Fitzgerald et al., 2011; Kokosalakis et al., 2020). Emissions depend on the type of fuel used, the type of engine, and its efficiency. Marine fuel oil, Heavy fuel oil, and Marine diesel oil are the most often utilized fuels in maritime vessels (Walker et al., 2018; Schnurr and Walker, 2019; Zincir, 2020). In 2019, annual atmospheric concentrations of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) have reached averages of 410 ppm, 1866 ppb, and 332 ppb respectively (IPCC, 2021) and if storage and use methods are not developed, future increases will lead to catastrophic problems of climate change (Al Baroudi et al., 2021). It is critical to highlight that global warming, in the 21st century, will increase by 1.5°C and 2°C unless GHG emissions are significantly reduced in the next few decades (IPCC, 2021).

The fourth International Maritime Organization (IMO) GHG study demonstrated that shipping transportation is accountable for 2.89% of global CO₂ emissions (IMO, 2021a) whereas CO₂ emissions from the business-as-usual scenario of shipping will probably increase up to 250% by 2050 (IMO, 2015; Bouman et al., 2017; Gritsenko, 2017; Tatar and Ozer, 2018) if no mitigation action will be taken (Bouman et al., 2017; Inal et al., 2021). Paris Agreement aimed to keep the century’s average temperature rise to 2°C; however, reductions in GHG emissions from maritime transportation were not included in the plan (Halim et al., 2018; Muhammad and Long, 2020). In abatement strategies that seek to preserve global GHG concentrations around 450 ppm or 550 ppm, all forms of transportation would be needed to significantly increase fuel efficiency, utilize more low-carbon fuels, and implement behavioral changes (Cames et al., 2015). The objective of the Paris Agreement for limiting the global temperature rise would be jeopardized unless the maritime sector contributes towards climate mitigation strategies (Halim et al., 2018).

However, the IMO approved a resolution in 2018 to cut shipping emissions by at least 50% and CO₂ emissions by at least 70% by 2050 (Chen et al., 2019; IMO, 2019; Muhammad and Long, 2020; Zincir, 2020). Considerable resources and investments are required to achieve this goal (UNCTAD, 2020). Merk (2014) projected that Asia and Africa will witness the largest increases in emissions because of substantial port traffic development and insufficient mitigating efforts. Therefore, mitigation strategies are necessary for all types of sea-going vessels, but the gravity of the problem needs to be identified first which is a major challenge in developing countries including Pakistan.

Existing studies now including the IMO studies have some sort of shortcomings, for instance, the fourth IMO GHG study has only covered ships of 100 GT and above. The omission of fishing vessels and other small commercial vessels from IMO’s GHG studies is also reported in a study in the United Kingdom (Coello et al., 2015). In addition, the national GHG emission scenario is also not provided. So, there is a question that arises where Pakistan is ranked among other countries in the breakdown of GHG emissions. It is critical to mention that significant gaps regarding the under-reporting of fuel data (IMO, 2009), the unavailability of Automatic Identification System (AIS) data for some years during the study period (IMO, 2015), and no reporting of fuel consumption data to International Energy Agency (IEA) by countries except a few ones (IMO, 2015; 2021b) have been reported in IMO’s GHG Studies. Accurate estimation of GHG emissions is vital for providing credible input to policy-making processes and climate response (Notte et al., 2018). So, the aforementioned gaps raise the question regarding the accurate calculation of global GHG emissions from maritime vessels of all types and sizes.

On the other hand, in the case of Pakistan, the actual national inventory of GHG emissions vis-à-vis all types/sizes of vessels is so far not established. Moreover, the allocation of emissions from ships has been hotly disputed based on the nationality of the transporting firm, country of departure, or the area where the fuel is sold, etc (Villalba and Gemechu, 2011a). GHGs and other air pollutants are considered transnational issues because they have no boundaries. However, a transnational issue doesn’t mean that you should put your emissions in the hands of others; rather, everyone must come up with climate mitigation plans and strategies. Therefore, the case of Pakistan is significant due to the large number of fishing vessels that are active in the Arabian Sea. Their cumulative effect, along with other types/sizes of vessels, on GHG emissions is unknown. Therefore, the establishment of a baseline reference scenario and knowing the carbon offset cost is crucial to know the actual gravity of the problem to contribute toward climate mitigation response as well as fulfillment of objectives and targets set under the National Climate Change Policy (NCCP) 2021 (GoP, 2021a) and Nationally Determined Contribution (NDC) 2021 (GoP, 2021b).

Hence, this entailed the need to explore and assess the overall GHG emission scenario from the most ignored and unattended segment of the maritime economy. In this context, this paper tried to analyze the potential GHG emissions for all types and sizes of sea-going vessels and their carbon offset cost by taking the case of a developing country i.e. Pakistan. The outcome of the study provides a baseline reference scenario for the GHG inventory and adds knowledge to the existing pool of literature which would help in developing policy and climate mitigation strategies specific to all types of maritime vessels.

This section demonstrates the amount of greenhouse gas emissions resulting from the maritime transportation sector of Pakistan and the carbon offsetting costs for maritime vessels. This assessment would provide insight into the most neglected sector that how all types of vessels vis-à-vis sizes are contributing towards national emissions as a silent contributor. As part of this study, the GHG emissions load of all sea-going vessels and their respective Global Warming Potential (CO₂e) is studied separately.

The overall results of the study revealed that the total GHG emissions from all types and sizes of maritime vessels (excluding naval platforms) in Pakistan are 2,468,789.21 tonnes (CO₂e) as a result of annual fuel consumption of 310,885.75 tonnes for the period 2021–2022. The business-as-usual case of all types and sizes of maritime vessels in Pakistan has a 4.9% share of reported total emissions from the transportation sector i.e. 51.3 million tonnes (CO₂e) in Pakistan’s updated NDC 2021 (GoP, 2021b). Whereas, Pakistan’s Second Communication on Climate Change had reported only a 1% share (0.413 million tonnes CO₂e) of maritime vessels in overall transportation sector GHG emissions i.e. 41.197 million tonnes CO₂ (GoP, 2018). (Villalba and Gemechu 2011a) highlighted that the allocation of shipping emissions has been the subject of significant controversy (Villalba and Gemechu, 2011b). Although there is a conflict about which emissions should be counted or not counted in the national GHGs inventory vis-à-vis concerns about international voyage-based emissions, the emissions of PNSC’s merchant ships and other crafts should be counted towards the flag state of maritime vessels considering the responsibility, commitments, and strategies of a country towards climate mitigation response.

It is significant to mention that fishing vessels are the largest emitters of GHG emissions (CO₂e) accounting for 1,731,638.32 tonnes among all types of sea-going vessels and have a 70% share of the total GHG emissions from the maritime transportation sector. During interviews with various boat owners and Nakhudas from Sindh and Baluchistan, it was found that all kinds of fishing are banned during breeding seasons in June and July. Above mentioned fishing vessels’ emissions are for 10 months excluding June and July. Even then, fishing vessels have dominated as the highest emitters of greenhouse gases.

On one side, fishing vessels, recreational and other crafts collectively are responsible for 75% of the total maritime emissions which are ignored and unaccounted for in the national GHG inventories. It is also quite evident from the study of Parker et al. (2018) that marine fishing fleet is often excluded from global GHGs assessments. The findings of this study revealed that the global fishing fleet accounted for 179 million tonnes of CO₂e as a result of 40 billion liters of fuel consumption in 2011 (Parker et al., 2018). On the other side, IMO covered ships of 100 GT and above only for the estimation of global GHG emissions, ignoring ships below 100 GT in which a large number of maritime vessels fall. Fishing vessels, recreational and other crafts are used for multiple purposes in a huge number, and a substantial amount of fuel is consumed, which has not received due attention from authorities or policymakers at the national or international levels. How can the role and impact of the aforementioned vessels be ignored when they have the highest and most significant share of GHG emissions in the maritime sector? Supporting evidence is also reported by Coello et al. (2015) and Endresen et al. (2007) that a significant underestimating of emissions from the maritime sector is non-etheless anticipated to occur from the exclusion of fishing vessels below 100 GT.

Alarmingly, the contribution of GHG emissions from the business-as-usual case of maritime vessels would exceed the calculated value when the fuel consumption of naval ships will be taken into account. Moreover, this study’s results are based on the tier one approach developed by IPCC which relies on fuel consumption data of ships viz-a-viz fuel type. Emissions from maritime vessels would be much higher when detailed studies will be done based on activity-based methods including various aspects of vessel characteristics. The same evidence is also reported by Chang and Wang (2012) and Chang et al. (2013) which highlights the need for a more in-depth analysis of GHG emissions from ports.

The findings of the study by Chang et al. (2013) indicated that the results of GHG emissions from port vessel operations based on an activity-based approach were five times higher than that estimated employing a top-down approach. Therefore, in-depth analysis will assist port authorities in better monitoring GHG emissions and developing GHG emission reduction policies (Chang et al., 2013). However, this study is also significant because this initial preliminary assessment provides insight into the actual gravity of the problem and scale and trend to foresee its share in national transportation. It is critical to highlight that the Government of Pakistan would require 37, 090, 381.57 US$/annum for offsetting carbon emissions i.e. 2,468,789.21 tonnes (CO₂e) with an average current market price factor of 15$/tonne CO₂e. However, a developing country like Pakistan which is least responsible for the global rising level of GHG emissions (GoP, 2021b) than developed countries but is among the top ten most vulnerable countries (Eckstein and Kreft, 2020) needs to adapt to and mitigate by ensuring a vibrant climate governance framework to combat the emerging climate crisis.

As long as the implication of the carbon offset scheme vis-à-vis mangrove forests is concerned, Pakistan needs approximately 20,020 hectares of mature mangrove forests to remove 2,468,789.21 metric tonnes of CO₂e emissions from the atmosphere in a timeline of 1 year. Mangroves are considered one of the most economically effective methods for offsetting carbon emissions because of their massive carbon sequestration potential ranging from 4–10 times more than terrestrial forests (dslb; GreenBiz Group, Inc., 2022). Taillardat et al. (2018) also suggested that mangrove blue carbon strategies are the most effective for climate mitigation at the national level. Now is the time to wake up and take necessary actions and measures to fight against the frightening level of GHG emissions at all levels. The Government of Pakistan must encourage the afforestation of mangroves to deal with the real issue of climate change by offsetting carbon emissions and combatting the climate crisis, successful and effective implementation of which will prove to be fruitful in the years to come.

The findings of this study revealed that the total greenhouse gas emissions, including carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), from the maritime transportation sector of Pakistan, are 2,468,789.21 tonnes (CO₂e) resulting from fuel consumption for the period 2021–2022. The business-as-usual case of all types and sizes of maritime vessels in Pakistan has a 4.9% share of the reported total transportation sector’s emissions in Pakistan’s updated NDC (2021) whereas, Pakistan’s Second Communication on Climate Change had reported only a 1% share of maritime vessels in overall transportation sector GHGs emitted in 2015. Carbon dioxide emissions from maritime transportation amounted to 2,423,211.88 tonnes whereas methane (CH₄) and nitrous oxide (N₂O) emissions are 1152.77 tonnes and 56.23 tonnes respectively. It is identified that 37, 090, 381.57 US$/annum is required for offsetting carbon emissions. As long as the implication of the carbon offset scheme vis-à-vis mangrove forests is concerned, Pakistan needs approximately 20,020 hectares of mature mangrove forests to remove 2,468,789.21 metric tonnes of CO₂e emissions from the atmosphere in a timeline of 1 year. The study’s findings provide a baseline reference scenario for future studies and national GHG inventory and add knowledge to the existing pool of literature which would help in decision-making processes, policy development, and climate mitigation strategies for all types of maritime vessels. Based on the findings of this study, the federal government is suggested to devise a proper mechanism for monitoring of carbon footprint of sea-going vessels and maintaining a periodic GHG emissions inventory by considering the outcome of this study as a baseline reference scenario and launch a GHG emissions reduction programme through shifting maritime vessels to low-carbon or zero-carbon alternative fuels. Besides, this study gives dimensions to future studies to assess the GHG emissions scenario of maritime vessels by employing a bottom-up approach and proposing effective climate mitigation measures for the maritime transportation sector of Pakistan. In addition, this study is limited to the assessment of three GHGs (CO₂, CH_4, and N₂O) resulting from fuel consumption only hence it opens doors for future researchers to explore and analyze the rest of GHGs and other non-GHGs emissions from the maritime transportation sector of Pakistan depending on data availability.