Current models estimate global aviation contributes approximately 5% to the total anthropogenic climate forcing, with aerosol-cloud interactions having the greatest effect. However, radiative forcing estimates from aviation aerosol-cloud interactions remain undetermined. There is an expected significant increase in aircraft emissions with aviation demand expected to rise by over 4% per year. Soot may play an important role in the ice nucleation of aircraft-induced cirrus formation due to a high emission rate, but the ice nucleating properties are poorly constrained. Understanding the microphysical processes leading to atmospheric ice crystal formation is crucial for the reliable parameterization of aerosol-cloud interactions in climate models due to their impact on precipitation and cloud radiative properties. Ice nucleation of aircraft-emitted soot is potentially affected by particle morphology with condensation of supercooled water occurring in pores followed by ice nucleation. However, soot has heterogeneous properties and undergoes atmospheric aging and oxidation that could change surface properties and contribute to complex ice nucleation processes. This review synthesizes current knowledge of ice nucleation catalyzed by aviation in the cirrus regime and its effects on global radiative forcing. Further research is required to determine the ice nucleation and microphysical processes of cirrus cloud formation from aviation emissions in both controlled laboratory and field investigations to inform models for more accurate climate predictions and to provide efficient mitigation strategies. Aerosol particles can facilitate ice crystal formation in clouds that affect Earth's precipitation and climate by altering the amount of sunlight that clouds reflect and is absorbed by Earth. Human-induced pollution may affect atmospheric ice nucleation, such as black carbon (soot) from aircraft emissions. It has been known for decades that carbon dioxide is a major greenhouse gas emitted from aircraft that significantly warms Earth's surface, but the climate effects of aerosol-cloud interactions are still largely unknown. An understanding of what aerosol particles in the atmosphere contribute to ice nucleation is needed to better predict how they will affect future climate. This review summarizes what we currently know about ice nucleation processes from aircraft soot emissions and identifies future research priorities to understand human-induced ice cloud formation to better predict how it may affect global climate. Ice nucleation is a current major uncertainty in predicting future climate from aerosol-cloud interactions This review synthesizes the current state of knowledge on ice nucleation from anthropogenic aircraft emissions Future research includes direct observations and laboratory measurements of ice nucleation microphysical processes from aircraft emissions

Observational evidence demonstrates that marine organic aerosols (MOA) are able to act as ice nuclei. MOA explains a substantial portion of the submicron marine aerosol, so that they have the potential to effectively influence marine cloud microphysics and cloud radiative forcing. This study provides the first evaluation of the radiative forcing and climatic impact of marine organic aerosols as ice nuclei on a global scale. MOA is implemented into a coupled aerosol and general circulation model. It is found that MOA contributes to more ice formation than dust or black carbon/organic matter in mixed-phase clouds. They also have a significant impact on the ice water path in the Southern Hemisphere and therefore could be an important missing source of ice nuclei in current models. The addition of MOA as natural heterogeneous ice nuclei reduces the magnitude of the total top-of-atmosphere anthropogenic aerosol forcing by as much as 0.3 W/m(2).