This paper presents a timely and topical research. It directly compares the marine cloud brightening (MCB) with the stratospheric aerosol injection (SAI) effects by utilizing the fully coupled atmosphere-ocean simulations. The study also reveals some new side effects by the MCB geoengineering, such as the locking of the climate into a permanent La Nina state and an increase in sea-level over the south Pacific Ocean. Those effects should be taken into account when developing geoengineering plans.

This article offers a wide ranging review of current understanding of the role various tropical cirrus cloud types play in the redistribution of water within the atmosphere and how they affect the changing Earth's energy balance by reflecting sunlight and preventing the escape of thermal energy to outer space. Improved understanding of these dynamics has been identified as critical for predicting whether such clouds may amplify or slow future global climate change. A clear exposition is provided of the various methods used to study tropical cirrus cloud characteristics and processes, including remote sensing, in situ measurements, modeling and laboratory work. Key questions include identifying how small-scale microphysical processes affect larger cloud structure, and how cirrus altitude and extent responds to changing radiation and thermodynamic profiles. A call is made not only for improved representations of cloud processes at finer scales, but also for a more holistic approach using a hierarchy of model detail. Such efforts would enable new knowledge obtained from studying even the smallest scales to be more readily placed within a broader context applicable to climate studies.

This personal tribute, authored by close colleagues and friends, is an homage to Paul Crutzen's profound and multifaceted impact in the field of atmospheric chemistry and physics. The article summarizes not only the exceptional breadth of research ranging from tropospheric ozone formation to stratospheric ozone loss, and coining the term ‘anthropocene’ but it also describes Paul Crutzen’s instrumental role in shaping the next generations of atmospheric scientists, many of whom now are leaders in the field. Furthermore, Crutzen’s legacy is manifested by his contributions to the creation of the journal Atmospheric Chemistry and Physics (ACP), that laid the foundation for EGU's pioneering open-access publication model, fostering public peer review and interactive scientific discourse.

Black carbon is a key source of uncertainty in regional climate predictions through aerosol-radiation interactions, cloud modifications and enhanced snow melt, and the arctic is particularly sensitive to these effects. Understanding the influence of continental emissions on arctic aerosols is crucial in earth system science, and this influence can be expected to evolve with changes to the atmospheric circulation in response to climate change. This paper uses a machine learning approach to study the factors controlling observations of black carbon in the arctic and quantitatively links these to meteorological processes and trends. This phenomenological assessment will facilitate predictions in the long range transport of black carbon transport under various climate change scenarios.