Using statistical methods and a set of ensemble climate models, we decompose the sources of Atlantic Meridional Overturning Circulation (AMOC) variance. Three distinct phases of physical variability are identified: from 1850 to 1990, internal variability dominates; from 1990 to 2050, dynamical adjustment related to AMOC decline takes over; after 2050, differences between forcing scenarios become dominant. Beyond these physical factors, model variability remains a major source of uncertainty.

Climate models serve as good guesses of how humans affect the climate, but they cannot explore all possible future scenarios of interest. We develop a method that can serve as a fast and cheap stand-in to evaluate likely changes in variables like surface temperature and relative humidity at a regional scale in arbitrary future climates. Crucially, our method captures relationships between different geographic areas and predicts both average values and likely ranges using a unified framework.

We analyze the duration of large-scale weather patterns and their link to near-surface temperatures during heatwaves in Central Europe for 1950–2023. Compared to non-heatwave days, a stronger link between them is found on heatwave days from May to September. We relate our results to typical long-lasting weather patterns known as weather regimes. In July and August, weather patterns last longer as west winds are often blocked by Scandinavian and European blocking regimes, inducing hot extremes.

In this study, we find that global freshwater storage on land (excluding Greenland and Antarctica) will likely decrease much more than raw models suggest – about 83 millimeters less water by 2100. This means that earlier studies may have overestimated future water availability. When we correct the models using observations, the results consistently show significant declines in freshwater, which could worsen water stress worldwide if demand continues to grow.

Geological evidence indicate persistent tropical sea-ice cover in the deep past, often called Snowball Earth. Using a climate model, we show here that clouds substantially cool down the tropics and facilitate the advance of sea-ice into lower latitudes. We identify a critical threshold temperature close to 0 °C from where cooling down the Earth is accelerated. This value can be used as a constraint on Earth's sensitivity to CO₂, as recent cold paleoclimates never entered Snowball Earth.