Search

Abstract Disentangling the impact of climate change on environmental extremes is of key importance for mitigation and adaptation. Here we present an automated system that unveils the climate change signal of the day in near-real-time, employing a set of innovative storyline simulations based on a coupled climate model. Its potential to complement probabilistic assessments is showcased for storm Boris, which brought record-breaking rainfall over Central and Eastern Europe in September 2024, leading to devastating floods. Our near-real-time storylines suggest that storm Boris deposited about 9% more rain due to human-induced warming. The area impacted by the same storm’s extreme rainfall (>100 mm) was 18% larger and would continue expanding in a future warmer climate. Results from our prototype storyline system are disseminated publicly via an online tool. The case of Storm Boris demonstrates the potential of near-real-time storylines for rapid evidence-based climate change communication.

Abstract Marine heatwaves are expected to become more frequent, intense, and longer-lasting in a warming world. However, it remains unclear whether feedback processes could amplify or dampen extreme ocean temperatures. Here we impose the observed atmospheric flow in coupled climate simulations to determine how the record-breaking 2019 Northeast Pacific marine heatwave would have unfolded in preindustrial times, and how it could unravel in a +4 °C warmer world compared to present-day conditions. We find that air-sea interactions, involving reductions in clouds and ocean mixed-layer depth and air advection from fast-warming subpolar regions, modulate warming rates within the marine heatwave. In a +4 °C warmer climate, global oceans are +1.9 °C warmer than present levels, and regional mean warming in the Northeast Pacific can reach +2.3–2.7 ± 0.25 °C. Our identified feedback processes are projected to further amplify the intensity and spatial extent of analogous Northeast Pacific summer marine heatwaves beyond those thresholds, with a warming reaching +2.9 ± 0.15 °C above present levels. Such an event-specific amplification would place even greater stress on marine ecosystems and fisheries.

This paper presents a new heatwave (HW) detection algorithm that identifies spatially coherent HW patterns on synoptic scales and their temporal evolution, yielding the main characteristics (extension, intensity or persistence) of HW events (HWEs). The algorithm has been applied to temperature data from the ERA-Interim reanalysis in order to derive a catalogue of Iberian HWEs for the extended summers (June to September) of the 1979–2017 period. The results indicate mean frequencies of five Iberian HWEs and 16 summer days with HW conditions over Iberia (Iberian HWDs), with significant positive trends in both diagnostics. The analysis of the life-cycle reveals that more than half of the HWEs correspond to events that originated within the region. Although Iberian HWEs last more than one week on average, they tend to be transient, persisting for about three days in the region (Iberian phase), where they reach maximum intensity and extension, and evolving later to other areas. In order to identify recurrent patterns of occurrence, a clustering of Iberian HWEs was performed based on their mean temperature fields. Four clusters were obtained: Atlantic, Subtropical, European and Mediterranean events, which display distinctive characteristics and spatio-temporal evolution, causing HW conditions in western, southern, northern and eastern Iberia, respectively. Interestingly, Mediterranean events largely explain the overall trends in Iberian HWEs and HWDs.The connection between Iberian HWEs and atmospheric circulation patterns as summarized in four Weather Regimes (WRs) was also investigated. During the Iberian phase, HWEs are preferentially associated with ridge conditions in western Europe, with small variations in this WR determining different regional HWEs. However, the four types of regional Iberian HWEs tend to occur under different WRs during their pre- and post-Iberian phases, and show different relationships with WRs on seasonal scales. Using an impact-oriented metric for HWEs that accumulates the intensity of HW conditions over the areas affected by the event through its life-cycle, the top 10 Iberian HWEs were identified. They include well-known recent events such as those of August 2003, and June 2017. Flow analogues of the most outstanding Iberian HWEs reveal that recent warming has contributed to double their extension and intensity, making them more exceptional than they would have been in the past.