This review explains how weather patterns, guided by the polar jet stream, influence the Baltic Sea’s climate and ecosystem. It covers the North Atlantic Oscillation, blocking events and other processes and discusses how they affect temperature, rainfall, and storms from days to decades. These shifts then impact oxygen levels, productivity, and acidification in the Baltic Sea. Physical links are fairly well known, but biogeochemical pathways remain uncertain.

Global mean surface temperature anomalies in 2023 and 2024 were the highest on the modern record. We quantify contributions to these anomalies from human activity, including the steep reduction in sulfur emissions from ships that began in 2020, and numerous natural factors. We attribute about 92% of the observed anomalies to a combination of various human-induced and natural factors, including important contributions from the reduction in marine sulfur emissions and the Indian Ocean Dipole.

There is a dangerous amount of uncertainty in our predictions of climate change in polar regions because some of feedbacks that might lead to changes that are too rapid for us to adapt to, or that cannot be reversed. We have run a set of simulations with a state-of-the-art Earth System Model that helps improve our understanding of how climate in these regions might change. Some of the aspects we investigate are reversible but many are not, especially those affecting ice sheets and sea level.

Multi-model ensembles are a key approach in climate model analysis, but their use involves many complex considerations. In this work, we review relevant literature and synthesize existing studies to contribute to the development of guidelines for designing and conducting ensemble analyses. This is complemented by a collection of useful resources and a discussion of emerging trends, supported by statistics tracing the number of publications.

In this work, we apply a novel quantifier, the spatial permutation entropy, to sea surface temperatures obtained from two commonly used products: ERA5 and NOAA OI v2 (NOAA Optimal Interpolation version 2). We report small scale differences between these products, as well as persistent trends at the large scale, which could be a consequence of global warming. We also report sudden changes that were not uncovered before, which correlate with different changes in the methodology or data sources of the products.

This study revisits how critical thresholds for tipping of the Atlantic Meridional Overturning Circulation (AMOC) are derived from comprehensive climate models. It is shown that the method for keeping the global salinity constant – by compensating salinity either at the surface or throughout the ocean volume – matters for AMOC tipping: with surface compensation, the tipping point shifts to larger freshwater forcing values, mainly due to (artificial) salt input in the North Atlantic and Arctic.

The Alps host glaciers, distinct ecosystems, socio-economic interests and water resources that are being impacted by climate change. In this study, we aim at understanding how warming occurs in the Alps in projected scenarios and what physical processes drive it. We find under these scenarios that elevations around the snowline will warm faster than elsewhere, because snow retreats to higher elevations. Indeed, snow slows down warming due to its high albedo and the energy consumed to melt it.

We studied how plants respond to long droughts using model simulations and satellite data. The model reproduces drought impacts fairly well but tends to show plants recovering too quickly. Improving how the model represents plant stress and recovery will help predict how ecosystems respond to more frequent and severe droughts in the future.