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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.

This paper provides key insight into the methodology of Working Group III of the IPCC Sixth Assessment Report on climate mitigation. The paper will be essential reading for anyone wishing to understand the assessment of climate outcomes of mitigation pathways in the context of the Paris Agreement.

The NHESS paper “A climate-conditioned catastrophe risk model for UK flooding” by Bates and colleagues presents and validates a new flood model for the UK that simulates pluvial, fluvial and coastal flood risks at a resolution of 20 to 25 metres. The authors then use their scheme to estimate the probability-loss distribution for UK flooding under various future climate and policy scenarios. Their paper provides the most detailed and realistic analysis to date of current and future flood risk in the UK. The key findings of their work are: (1) Previous UK flood losses based on government data and used in national climate change risk assessments are overestimated by a factor of about 3. (2) Official UK estimates lie well outside the paper's modelled loss distribution, which is plausibly centred on the observations. (3) The UK 1% annual probability flood losses were only about 6% greater in the average climate conditions of 2020 than for the period of historical river flow and rainfall observations (centred approximately on 1995). (4) Increases in risk can be kept to around ~8% if all COP26 2030 carbon emission reduction pledges and ‘net zero’ commitments are implemented in full. (5) Implementing only the COP26 pledges increases UK 1% annual probability flood losses by ~23% above recent historical values, and potentially ~37% if climate sensitivity turns out to be higher than currently thought.

The manuscript presents a reconstruction of global temperature spanning the Holocene, which extends the scope of previous exercises in palaeoclimate data assimilation. The resulting reconstruction presents new insights into changes in global temperature over this period. Most notably, it confirms the results of previous studies that have shown a global cooling trend over the past 6,000 years. It also shows that a cooling trend is found even after allowing for potential biases in the proxies. These results are likely to be of considerable interest to the broader geoscience community.

This paper examines the warning deficits in conjunction with the major flooding event in Germany of summer 2021. The event caused many fatalities and enormous damage. The warning procedures proved to be insufficient, and after investigations it was decided to install a cell broadcast system in Germany, which is already in place today. The deeper investigations on the warning perceptions and the influencing factors is of major interest to readers beyond the scientific community.

Tipping points have potentially major detrimental impacts on natural and human systems. This study highlights how the rate of change in external conditions is arguably one of the key tipping mechanisms for both natural and human systems in the human-dominated anthropocene. This notion of rate-induced tipping -- namely an instability that occurs when external conditions vary faster than some critical rate -- will likely become an increasingly important topic of scientific research in the coming years.

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

This article describes the effect of the recent (January 2022) Hunga Tonga-Hunga Ha’apai volcanic eruption on the stratosphere. The eruption was highly energetic and as a result erupted material reached altitudes of around 30km. Such eruptions, with the 1991 Pinatubo eruption being a noteworthy example, often have a significant effect on tropospheric weather and climate, through the radiative effects of the volcanic aerosol, which may remain in the stratosphere for 2 or 3 years or more. In the 30 years since the Pinatubo eruption observations of the stratosphere, primarily from satellites, have improved enormously and in this Letter the authors provide a detailed description of the evolution of volcanic aerosol and of other chemical species injected by the eruption over a 6-month period following the eruption. The authors show that one important effect of the eruption was to inject a large quantity of water vapour into the stratosphere and suggest that the largest impact of the eruption on tropospheric weather and climate will be via the radiative effect of this water vapour, rather than of the injected aerosol. The initial detailed picture of the impact of the Hunga Tonga-Hunga Ha’apai eruption on the stratosphere provided in this Letter will stimulate further study of this remarkable natural event, which provides a rare opportunity to test our scientific understanding.

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.

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.

The health of the amazon ecosystem is a key indicator of the health of our planet. Hence, the editor feels that this paper will attract the attention of a broad audience and the media.

I agree with the handling editor and suggest considering it as a highlight paper.

Paleontological knowledge transfer can be fun! This extended review paper of comics and graphic novels on the subject of paleontology discusses the potential for communicating paleontological topics to the public and the influence of contemporary paleoart in this genre. Additionally, the motivation for and the creation process of the bilingual graphic novel "EUROPASAURUS - Life on Jurassic Islands" - intended as modern science communication - is described. An extensive survey among readers of this book allows conclusions as to what the public expects and appreciates in such a work.

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.

Achieving both performance and portability in a whole dynamical core implemented in a high-productivity language such as Python is an eye-opening result which rebuts some widely held assumptions in the geoscientific modelling community. This is a paper which everyone who writes geoscientific models should read.

The study by Franz et al. provides exciting new insights into deep biosphere processes during the 'boring billion', indicating that fungi-like eukaryotic organisms developed before 1 Ga and that a deep continental biosphere was already present in the Early Mesoproterozoic/Late Paleoproterozoic.

This paper clearly demonstrates the value of the rescue of historical meteorological data, as they help to come to a better assessment of the characteristics of events in the past. Using such data, the study is able to give evidence for physical processes of particular relevance for the intensity of an historical hazardous event. The approach makes an assessment of such events in the context of climate change and variability possible.

I think the paper contains some important messages for the management of soil water that have widespread implications

Understanding how sediment moves in rivers is fundamental to the shape of our landscapes and how they evolve. A key part of this understanding is measuring the size and shape of cobbles, pebbles and grains in the bed of a river. Often this measuring task is laborious and carried out by hand. However, this paper presents code and describes a method for measuring this using 3d point cloud data (from a laser scan for example) enabling the automation and rapid measurement.

Summer 2022 was memorable and record-breaking in much of Europe - for example heatwaves in France. This paper discusses marine heatwaves in the Mediterranean and northeastern Atlantic Ocean and their importance for European climate. It investigates the causes of increased sea surface temperature during summer 2022 for the seas around France through assessing the different atmospheric fluxes determining the upper ocean heat budget. It highlights the need for continuous monitoring of the ocean surface in order to assess the impact of these marine heatwave events.

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.

Stratospheric aerosol injection (SAI) is often discussed in the media and in policy circles as a possible action to limit future increase in global temperatures. Indeed it has been demonstrated in model simulations that in principle injection could be 'controlled', using model information, to meet specific targets on the temperature increase and its spatial distribution. This paper shows that the simulated climate response to SAI is strongly model-dependent, reflecting fundamental uncertainties in model representation of key processes. In particular this means that the SAI determined by the control algorithms as those required to achieve temperature targets different significantly from one model to another. Specific mechanisms, in particular the difference in rapid response in clouds and in precipitation to an imposed radiative perturbation and the ensuing ocean circulation response, are identified that contribute to the strong differences in model response to SAI. There is also a strong sensitivity to the pre-existing sulphate distribution which will be determined by future anthropogenic emissions. The authors note that these inter-model differences are unlikely to be resolved quickly and that controlled SAI, to achieve specific temperature goals and with well-quantified risks of unexpected consequences, is likely to remain out of reach for many years.

Many papers are currently being published applying deep learning to geoscientific applications. However, most of them only offer proof of concept results on highly idealised scenarios. This paper combines deep learning approaches with the structural causal models popularized by the work of Judea Pearl, and it applies this methodology to a real problem, analyzing soil moisture-precipitation coupling in climate reanalysis data. In contrast to many papers in this field, this promises actual insight in the scientific application of the work.

Emissions from conventional aircraft contribute to climate change by forming contrails and by increasing atmospheric CO2 concentrations. To fly faster and reduce the climate impact, super- or hypersonic aircraft fuelled by liquid hydrogen or natural gas are being considered. Hypersonic aircraft would fly at more than Mach 4 in the stratosphere, up to 35 km altitude, where the peak of the ozone layer resides. The paper by Pletzer et al. presents a thorough study of the chemical and radiative impacts of such high-speed aircraft using two chemistry-climate models. The study shows that hypersonic aircraft fuelled by liquid hydrogen and cruising at such altitudes would contribute to a significant global warming although they do not emit CO2. The main radiative effect comes from additional water vapour, with only a small effect from depletion of the ozone layer. Importantly, the authors discovered that although water vapour is destroyed in the stratosphere, perturbation of local photochemistry also creates water vapour. The authors estimate that the mean surface temperature change caused by a hypersonic transport fleet would be roughly 8-20 times larger than for a subsonic reference aircraft with the same transport volume. This comprehensive study provides convincing calculations for a large climatic effect of any future hydrogen-fuelled hypersonic aircraft fleet.