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Implications of reduced-complexity aerosol thermodynamics on organic aerosol mass concentration and composition over North America

We implemented the BAT-VBS (Binary Activity Thermodynamics volatility basis set) aerosol thermodynamics model in the GEOS-Chem chemical transport model to efficiently account for organic aerosol water uptake, nonideal mixing, and impacts on the gas–particle partitioning of semi-volatile organics. Compared to GEOS-Chem's complex (dry) scheme, we show that the BAT-VBS model can predict substantial enhancements in organic aerosol mass concentration at moderate-to-high relative humidity.

Explaining the period fluctuation of the quasi-biennial oscillation

The paper addresses a fundamental but unresolved question about the tropical stratospheric wind oscillation: why does the period of the oscillation fluctuate irregularly? We use global reanalysis data to provide evidence that the oscillation period is primarily modulated by seasonal variations in small-scale atmospheric wave activity. The findings have implications for seasonal and climate predictions.

Quantified ice-nucleating ability of AgI-containing seeding particles in natural clouds

We analyzed the ability of silver iodide particles (a commonly used cloud-seeding agent) to form ice crystals in naturally occurring liquid clouds at −5 to −8 °C and found that only ≈ 0.1 %−1 % of particles nucleate ice, with a negative dependence on temperature. By contextualizing our results with previous laboratory studies, we help to bridge the gap between laboratory and field experiments, which also helps to inform future cloud-seeding projects.

Stratospheric residence time and the lifetime of volcanic stratospheric aerosols

The climate impact of volcanic eruptions depends in part on how long aerosols spend in the stratosphere. We develop a conceptual model for stratospheric aerosol lifetime in terms of production and decay timescales, as well as a lag between injection and decay. We find residence time depends strongly on injection height in the lower stratosphere. We show that the lifetime of stratospheric aerosol from the 1991 Pinatubo eruption is around 22 months, significantly longer than is commonly reported.

Pristine oceans are a significant source of uncertainty in quantifying global cloud condensation nuclei

Aerosol particles in the atmosphere increase cloud reflectivity, thereby cooling the Earth. Accurate global measurements of these particles are crucial for estimating this cooling effect. This study compares and harmonizes two newly developed global aerosol datasets, offering insights for their future use and refinement. We identify pristine oceans as a significant source of uncertainty in the datasets and, therefore, in quantifying the role of aerosols in Earth's climate.

Modulation of the northern polar vortex by the Hunga Tonga–Hunga Ha'apai eruption and the associated surface response

In January 2022, the Hunga Tonga–Hunga Ha'apai (HTHH) volcano erupted, sending massive amounts of water vapour into the atmosphere. This event had a significant impact on stratospheric and lower-mesospheric chemical composition. Two years later, stratospheric conditions were disturbed during so-called sudden stratospheric warmings. Here we simulate a novel pathway by which this water-rich eruption may have contributed to conditions during these events and consequently impacted the surface climate.

Modelled surface climate response to effusive Icelandic volcanic eruptions: sensitivity to season and size

We use an Earth system model to systematically investigate the climate response to high-latitude effusive volcanic eruptions as a function of eruption season and size, with a focus on the Arctic. We find that different seasons strongly modulate the climate response, with Arctic surface warming observed in winter and cooling in summer. Additionally, as eruptions increase in terms of sulfur dioxide emissions, the climate response becomes increasingly insensitive to variations in emission strength.

Opinion: Why all emergent constraints are wrong but some are useful – a machine learning perspective

In our article, we review uncertainties in global climate change projections and current methods using Earth observations as constraints, which is crucial for climate risk assessments and for informing society. We then discuss how machine learning can advance the field, discussing recent work that provides potentially stronger and more robust links between observed data and future climate projections. We further discuss the challenges of applying machine learning to climate science.

Opinion: Understanding the impacts of agriculture and food systems on atmospheric chemistry is instrumental to achieving multiple Sustainable Development Goals

We discuss our current understanding of and knowledge gaps in how agriculture and food systems affect air quality and how agricultural emissions can be mitigated. We argue that scientists need to address these gaps, especially as the importance of fossil fuel emissions is fading. This will help guide food-system transformation in economically viable, socially inclusive, and environmentally responsible ways and is essential to help society achieve sustainable development.

Warming effects of reduced sulfur emissions from shipping

A 2020 regulation has reduced sulfur emissions from shipping by about 80 %, leading to a decrease in atmospheric aerosols that have a cooling effect primarily by affecting cloud properties and amounts. Our climate model simulations predict a global temperature increase of 0.04 K over the next 3 decades as a result, which could contribute to surpassing the Paris Agreement’s 1.5 °C target. Reduced aerosols may have also contributed to the recent temperature spikes.

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