A recent study has pointed out an unexpected result of reduced shipping emissions—there has been a sudden and significant increase in global warming, Communications Earth & Environment highlights.
The study, titled Abrupt reduction in shipping emission as an inadvertent geo-engineering termination shock produces substantial radiative warming, states that human activities affect the Earth’s climate through modifying the composition of the atmosphere, which then creates radiative forcing that drives climate change. The warming effect of anthropogenic greenhouse gases has been partially balanced by the cooling effect of anthropogenic aerosols.
As explained, aerosols originating from the global shipping industry have an impact on cloud formation, essentially turning shipping emissions into a long-term unintentional experiment similar to marine cloud brightening (MCB). Beginning on January 1, 2020, the International Maritime Organization (IMO) enforced new regulations (IMO 2020) on the sulfur content in international shipping fuel, reducing it from 3.5% to 0.5%. Although aimed at improving public health by decreasing aerosol emissions, this reduction can temporarily intensify global warming by diminishing clouds over the world’s oceans.
The swift implementation of IMO 2020 suggests it likely has widespread effects globally, essentially acting as a “termination shock” for the inadvertent geoengineering experiment, leading to what can be seen as a reverse MCB—marine cloud dimming by reducing cloud droplet concentration.
Observations indicate that IMO 2020 has altered the occurrence and characteristics of ship tracks across oceans, showcasing how a regulation designed to curb pollution can have unintended consequences on cloud behavior. Analysis of remote sensing data has revealed evidence of cloud dimming particularly in the South Atlantic shipping lane. However, outside this region, the impact of IMO 2020 appears less spatially distinct, posing challenges for direct observation of its effects.
According to the study, by neglecting the heat uptake by the deep ocean over the short term (around 10 years), they estimated that the radiative forcing of 0.2 W/m² translates to approximately 0.16°C of warming over a timescale of 7 years. This corresponds to a warming rate of 0.24°C per decade, which is more than double the average warming rate since 1880 and 20% higher than the mean warming rate since 1980.
We also established the lower and upper bounds of the forcing and the associated expected warming. IMO2020 is projected to significantly accelerate the warming rate of global mean temperature throughout the 2020s, with the rate of warming rising sharply from 2020 and approaching the longer-term trend line by the end of the period.
..the study states.
The record warmth observed in 2023 falls within the projected trajectory, indicating that such warmth will become increasingly common in the 2020s. Overall, the mean temperature anomaly of the 2020s is forecasted to be 0.3°C higher than that of the 2010s. While estimating the warming effect of IMO2020 on sea surface temperatures (SST) regionally is challenging due to various influencing factors such as aerosol concentration, ocean circulation, and air-sea interactions, the pronounced geographical variations in the forcing imply significant variability among ocean basins.
