Global climate model development to constrain the impact of airborne microplastics on climate change

Because they are small and lightweight, airborne microplastics can remain suspended in the atmosphere for long periods. Microplastics appear to be ubiquitous in the atmosphere, having been identified at numerous remote sites and as high as 3500 m above sea level. Previously it has been shown that airborne microplastics may contribute to climate change by absorbing and scattering light. A weak cooling effect was calculated for direct microplastic-radiation interactions, subject to large uncertainties. Recent studies have identified the presence of microplastics in cloud water collected at high altitudes, suggesting that microplastics may act as cloud condensation nuclei (CCN). However, laboratory studies indicate that microplastics act as ice-nucleating particles (INP). The consequences of microplastics seeding cloud formation on climate change are unknown, as global climate models do not routinely include airborne microplastics, which are essentially a new class of anthropogenic aerosol. We present plans and progress for the implementation and assessment of microplastics as an aerosol species within GLOMAP-mode, the aerosol scheme used in the United Kingdom Chemistry & Aerosols (UKCA) component model of the UK Earth System Model (UKESM1.1). We aim to model microplastic-cloud interactions and their effect on climate so that together with microplastic-radiation interactions, the full effects of airborne microplastics on climate can be accounted for.