Climate models are indispensable tools for quantitatively predicting changes in global mean surface temperature in response to a doubling of atmospheric carbon dioxide concentrations. Despite decades of effort within the modeling community, large uncertainties persist. This opinion paper advocates for prioritizing the use of perturbed parameter ensembles (PPEs) as an effective strategy for reducing uncertainty in climate projections, rather than focusing on increases in model complexity or spatial resolution. Based on a synthesis of the existing literature, the authors evaluate the broad applicability and demonstrated effectiveness of PPEs and propose a strategic agenda for their expanded use within the climate modelling community.

New particle formation, or nucleation, is known to be a globally important source of atmospheric aerosol particles, based on observations and model simulations. However, much of the observational evidence of its importance is based on clear nucleation "events" driven by strong photochemical processes that peak during the daytime. Here, the authors show that over Central Amazonia nearly half of the Aitken-mode sized particles with diameters 10-25 nm stem from a slower but hitherto hidden production of particles. This discovery changes our understanding of aerosol budgets in the lower atmosphere, requiring a reappraisal of measurements and model simulations for this and other regions.

In recent years, there has been much interest in the extent and effects of synthetic chemicals on the environment. This work presents a novel technique used for the study of methylsiloxanes in atmospheric aerosol, a less well studied class of molecules used in lubricants, among other applications. The evidence presented shows they are present in the atmosphere at a surprisingly wide variety of scales.

This study presents the first multi-city observational assessment of fossil-fuel CO₂ emissions in major and mid-sized Chinese cities using Δ(¹⁴C) and δ(¹³C). The measurements reveal substantial declines in fossil-fuel CO₂ concentrations, consistent with documented reductions in coal consumption, increased reliance on natural gas, and notable improvements in combustion efficiency. However, the observed decreases are larger than those reported by bottom‑up emission inventories, suggesting that current inventories may systematically underestimate real-world CO₂ mitigation. These findings hold important policy implications for evaluating the effectiveness of China’s clean‑air measures and for advancing accurate urban emissions monitoring.