Ships

We collected international CO₂ shipping emissions for 2016–2018 based on EDGAR’s international emissions. We also collected global shipping emissions during the period of 2007–2015 from IMO³⁸ and ICCT³⁹. According to the Third IMO GHG Study³⁸, CO₂ emissions from international shipping accounted for 88% of global shipping emissions, and domestic and fishing emissions accounted for 8% and 4%, respectively. We calculated international CO₂ shipping emissions from 2007–2015 from global shipping emissions and the ratio of international to global shipping emissions. We extrapolated emissions from linear fits from 2007–2018 to estimate the emissions in 2019. The data sources of shipping emissions are listed in Table 5. We obtained emissions for the first half year of 2019 byassuming the equal distribution of monthly shipping CO₂ emissions. The equations are as follows:

Data sources used to estimate ship emissions.

α is the increasing rate of international shipping emissions in 2019 based on the linear extrapolation of data from the period 2007–2018, estimated to be 3.01%. Rmonth represents the ratio of the months to be calculated in the whole year. Given this, we estimated the shipping emissions for the first half year of 2019 using Rmonth equal to 181/365.

We assumed that the change in shipping emissions was linearly related to the change in ship traffic volume. The change in international shipping emissions for the first half year of 2020 was calculated according to the following equation:

where c_index represents the ratio of the change in shipping emissions, estimated to the end of April as −25% compared to the same period last year according to the news report⁴⁰.