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In 2020, a new international law was imposed that placed strong restrictions on sulfur emissions from the international shipping industry. In addition to reducing air pollution, an anticipated side effect was reduction of the climate cooling effect that is often associated with "ship-tracks". Aerosol pollutant emissions from ships, when they rise into overlying clouds, lead to higher cloud droplet number concentrations, smaller cloud droplet sizes, and clouds that are more reflective to incoming sunlight, easily seen in satellite imagery as long bright lines downwind of ships. Past studies into whether the new law has led to darker clouds have been equivocal. For this study, the authors used sophisticated statistical techniques to compare cloud droplet size and reflectivity before and after the law was implemented focusing on a shipping corridor in the southeast Atlantic. They found strong evidence that droplet sizes have indeed increased, and that clouds have darkened with a significant local climate warming. Globally, the impact is much smaller, but may still represent an important consideration for assessments of the total summed effect of aerosols on climate.

Tornadoes are having impact on peoples live and are in a general interest.

Machine Learning is a rapidly expanding technique in the field of weather and climate modelling. This paper takes stock of the state of the field at the present time, and will be invaluable to participants across the field and beyond who wish to understand the impact of Machine Learning on the field, its limitations, and current scope.

Sea level rise represents one of the most compelling aspects of anthropogenic climate change. The potential social and economic impacts are enormous, with little that can be done to mitigate them. It is therefore of critical importance that we are able to correctly anticipate these impacts in advance. This study presents a new, open-source platform that integrates numerical modelling with socioeconomic and physical datasets, whilst also allowing for the uncertainty in climate change projections. This tool therefore allows for new and improved estimates of the global costs of future sea level rise and is likely to be of widespread interest.

This paper proposes a novel method for translating past observed extreme weather events into current or future climates. It illustrates this with the analysis of an extreme windstorm that occurred in 1903. The latter storm would likely be more damaging if it occurred today rather than 120 years ago.

The role of chemical reactions within the atmospheric multiphase system, i.e. aerosol particles and cloud droplets surrounded by a gas phase, has been recognized for several decades to affect the atmospheric composition. In this article, significant advancements in measurement techniques during the past 20 years are briefly described that led to the identification of thousands of organic compounds and molecular-scale processes within the atmospheric multiphase system. Similarly, the complexity of multiphase chemistry models has been increasing to include in detail the underlying chemical processes and phase transfers between gas, aqueous, and organic phases. The authors propose how complementary techniques, such as machine learning and molecular dynamics, can be used to constrain the resulting model complexity. They also identify chemical parameters to be further constrained in lab and field studies. Overall, the article highlights the need and future directions of increasingly interdisciplinary efforts to characterize the atmospheric multiphase chemistry system and its impacts on climate-chemistry interactions, atmospheric oxidation capacity and human health.

This manuscript provides a novel and comprehensive assessment of uncertainty associated with sea level rise. The model description is thorough and it is applied to a number of possible scenarios. The conclusions are important for framing future discussions on sea level rise.

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 study addresses an important question regarding the stability of ice shelves, a question that is highly relevant for Greenland and Antarctica. Using a unique combination of observations, the authors document extensive thinning and extremely high basal melt rates at the floating tongue Nioghalvfjerdsbræ, North Greenland, an important and fast-changing part of the Greenland Ice Sheet. The increase in melt rates are suggested to be caused by an increase in surface melt that is funneling surface water under the ice shelf.

Ship tracks are enhanced regions of cloud brightness that trail behind ships that are known to be created by their effluent. They are widely used as observational test beds to deepen understanding of how pollution might affect cloud microphysical processes and climate at larger regional and global scales.  This study uses satellite observations of cloud properties and records of ship position and their effluent to assess perturbations from ship emissions on cloud droplet number and liquid water path. The study found that, as expected, the droplet number perturbation in shiptracks scales with ship emission rates of aerosol particles. Surprisingly, however, the liquid water path in drizzling clouds increased by an amount that was nearly fixed. The observation points to novel non-linear threshold behaviours of relevance to representations of aerosol indirect effects in climate models.

The paper provides the general overview on the upcoming EarthCARE mission, which carries a unique suite of active and passive instruments for aerosol, cloud and radiation observations. It is thought to be the introductory paper for the AMT Special Issue "EarthCARE Level 2 algorithms and data products".

This paper presents changes in thickness, flow and basal melt of Antarctic ice shelves over the past 26 years at relatively high resolution. An analysis based on an ocean model investigates the ice-ocean feedbacks. Overall, this is very useful for a large Antarctic research community.

The study covers a relevant contemporary topic (wildfire) and focusses on the recent major European summer of wildfires. The authors demonstrate that the assessment of burned area alone is not enough to fully characterize the impact of fires. Novel methods to assess burned area and above ground biomass losses are described to provide a more informative impact-based characterization of fires.

This paper is relevant and can be of interest for a wider audience. It is important that the effects of artificial snow on hydrology and water resources is discussed in a more technical, hydrological forum, like HESS. The paper shows important and sound conclusions which are relevant in the societal discussion on the effects of snowmaking.

The international Montreal Protocol was signed in 1987 in order to protect the atmospheric ozone layer by phasing out the production of halogenated hydrocarbons that deplete stratospheric ozone. The protocol was successfully implemented and, over the years, amendments and adjustments of the protocol were essential to its success. Ultimately, the protocol has resulted in a reduced halogen loading of the atmosphere since the mid-1990s. Trifluoromethane (HFC-23) is one of the substances regulated by the Montreal protocol since the Kigali amendment in 2016. HFC-23 does not deplete stratospheric ozone but is a very potent greenhouse gas. Commitments were made to reduce emissions of HFC-23 during the production of HCFC-22 as part of agreements in the protocol. However, the data presented and analysed in this paper indicate that in China more than the agreed amount of HFC-23 has been emitted since 2015, resulting either from unsuccessful factory-level HFC-23 abatement and/or inaccurate quantification of emission reductions. The analysis provides valuable data of atmospheric HFC-23. The study is also a good example of how compliance with the Montreal Protocol can be monitored.

This review paper constitutes a tremendous effort reviewing and analyzing a vast body of literature on the evaluation of Satellite Remote Sensing-based evapotranspiration datasets. It is a great road map for this field of research guiding all future such studies toward the use of community-based best practices.

This manuscript is published as SOIL Letters publication as it provides a timely and important contribution, formulating six fundamental principles for the robust study of soil carbon saturation. This is an important topic in research on soil carbon and its role in climate change mitigation which should be of interest to the wider geoscience community.

This provocative opinion piece examines the theoretical, numerical, and observational evidence in support of two highly cited proposed mechanisms for invigorating deep convective clouds through higher aerosol concentrations. Both start with high concentrations of water droplets. Through cold-phase invigoration, precipitation is reduced allowing for greater release of latent heat from freezing higher up in clouds. With warm-phase invigoration, increased latent heating occurs lower down due to accelerated liquid condensation. In both cases, the article persuasively argues from a variety of standpoints that the evidence to support the importance of the effects is weak, particularly once the full complexity of clouds and their interactions with their environment is fully taken into account. Concrete suggestions are made for improving definition, observations, and modeling of the problem, but also an admonishment that attention in the field might be better directed towards more fruitful aspects of the aerosol-cloud interaction problem.

This study assesses climate impacts on the economy and society of the USA, using a model that can downscale impacts to regional scale. The findings are thus both scientifically and policy-relevant.

The influence aerosols have on climate has long been recognised, but our ability to observe and quantify them on global scales came of age with the use of new satellite-based instruments and data products in recent decades. As instrumentation technologies improve alongside our abilities to handle large quantities of data and process using the latest data science approaches, the data products available to atmospheric science will only improve in decades to come. This opinion article tries to anticipate what tools and insights the community can look forward to in the near future.