Atmospheric Composition and Radiative forcing changes due to UN International Ship Emissions regulations (ACRUISE)

Lead Research Organisation: University of Leeds
Department Name: School of Earth and Environment


Ships generally burn low quality fuel and emit large quantities of sulfur dioxide and particulates, or aerosols (harmful at high concentrations), into the atmosphere above the ocean. In the presence of clouds the sulfur dioxide is rapidly converted into more particle mass growing them to sizes where they act as sites for cloud droplet formation. Given that about 70% of shipping activities occur within 400 km of the coast, ships are a large source of air pollution in coastal regions, causing 400k premature mortalities per year globally. In the UK, air pollution (including ship emissions) is responsible for 40,000 premature mortalities each year. In an effort to reduce air pollution from shipping activity, the United Nation's International Maritime Organization (IMO) is introducing new regulations from January 2020 that will require ships in international waters to reduce their maximum sulfur emissions from 3.5% by mass of fuel to 0.5%.

Particulates emitted by ships may enhance the number of cloud droplets and potentially form regions of brighter clouds known as ship tracks. Largely because of this effect, some global models predict that ship emissions of particulates currently have a significant cooling influence on the global climate, masking a fraction of the warming caused by greenhouse gas emissions. So whilst a reduction in ship sulfur emission is predicted to almost halve the number of premature deaths globally via a reduction in sulfate aerosols, a lack of similar reductions in greenhouse gases from shipping (e.g. CO2) could lead to an overall climate warming. However, the magnitude of the cooling caused by particulates is very uncertain, with large discrepancies between global model and satellite-based estimates. This may be due to imprecise representations of the effects of aerosols on clouds in global models or biases in satellite detections of ship tracks. Furthermore, how shipping companies respond to the 2020 regulation (i.e. degree and method of compliance), in international waters where surveillance is challenging, is largely unknown and requires observational verification.

We will take advantage of this unique and drastic "inverse geoengineering" event in 2020. By combining aircraft observations, long-term surface observations, satellite remote sensing, and process-level modelling, we will investigate the impact of the 2020 ship sulfur emission regulation on atmospheric composition, radiative forcing and climate in the North Atlantic. Results of this project will improve our understanding of the impact of ship emissions on air quality and climate.

Planned Impact

To reduce ship-derived air pollution in coastal regions, International Maritime Organisation (IMO) regulations require ships to reduce their sulfur emissions from a maximum of 3.5% to 0.5% in 2020. However, whilst a reduction in sulfur would help to improve air quality, a lack of similar reductions in greenhouse gases from shipping could lead to an overall, but highly uncertain, climate warming effect. We will take advantage of this unique "inverse geoengineering" event in 2020, by combining in situ observations, remote sensing, and process-level modelling to investigate the impact of the 2020 ship sulfur emission regulation on atmospheric composition and radiative forcing in the North Atlantic. Below, we describe a number of key beneficiaries of our proposed work:

General Public, Environmental Authorities, and Health Agencies:
Air pollution comes with huge health and financial costs. For example, particulate air pollution in the UK is estimated to reduce life expectancy by 6 months, with a cost to the national economy of £16 billion/year (DEFRA, 2015). Our project will increase the understanding of the impact of changing ship emissions on coastal air quality, contributing towards more accurate air quality forecasts in populated coastal regions, and allowing environmental authorities to mitigate and prepare, both practically and economically. This could have direct positive impacts on the health of the wider public, e.g. by providing early warnings to the public for periods of dangerously high air pollution that may be harmful to health. Health agencies will benefit from the potential cost savings associated with improvements to the health of the affected populations. Such benefits are likely to be felt soon after completion of the project (2 - 5 years), and will continue into the future.

Our work will directly benefit the IMO, the regulatory body responsible for ship emissions. Our proposed observations will provide valuable information on the percentage and spatial distributions of ships' compliance to the 2020 regulation over the open ocean, which is otherwise difficult to police. We will be able to start providing such information to the IMO soon after the 2020 regulation comes into force.
By increasing our understanding of the role of ship emissions on UK coastal air quality, this research will benefit key government advisory bodies, such as the Department for Environment, Food and Rural Affairs (DEFRA), and influence government policy via the Climate Change and Waste & Air Quality Directorates. The 2020 IMO regulation only deals with sulfur emissions, and thus emissions of other air pollutants (e.g. nitrogen oxides, ozone-precursors) may be 'business as usual'. We will also monitor these pollutants in ship plumes, and by communicating our findings to key policymakers (see Pathways to Impact), our work may influence government policy with regards to ship emissions in populated coastal areas within 3 - 5 years of the project end.

Scientific Bodies/Users:
Besides the effects on air quality, aerosols from ship emissions may cause a cooling of the Earth's climate through their interactions with clouds. Our project will benefit global climate bodies such as the UN Intergovernmental Panel on Climate Change (IPCC), by improving understanding of the climate sensitivity to ship emissions - vital if we are to meet the requirements of the UNFCCC COP21 agreement of limiting the global temperature rise this century to < 2 degC above pre-industrial levels. Academic beneficiaries include those working in fields of atmosphere, ocean, and Earth-system science. For example, the UK Earth System Model (NERC/Met Office collaboration) couples atmosphere/ocean processes to provide predictions of Earth's future climate. Our results will provide important constraints on the magnitude of the aerosol indirect effect in this model, contributing towards more accurate predictions of the future climate.


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Description We have quantified the aerosol radiative forcing caused by the IMO global emissions reductions that occurred on 1 January 2020. The global mean forcing is estimated to be about 0.3 W/m2, which is a substantial fraction of the total aerosol radiative forcing over the industrial period.

The UK Earth System Model (UKESM) substantially underpredicts sulfur species concentrations in the vicinity of the ship tracks that we have studied. These large biases and have been corrected. The effect of the model adjustments on the magnitude of aerosol radiative forcing in UKESM has not been evaluated yet, but could be substantial.
Exploitation Route Once confirmed, the results will have an impact on policy makers in relation to the Paris 1.5 degree target because the shipping emissions reduction has inadvertently caused a positive radiative forcing (i.e., warming).

Substantial model adjustments will increase our confidence in aerosol radiative forcing calculated using UKESM.
Sectors Environment,Transport