eleitl

Abstract

Mass loss from ice sheets in Greenland and Antarctica has quadrupled since the 1990s and now represents the dominant source of global mean sea-level rise from the cryosphere. This has raised concerns about their future stability and focussed attention on the global mean temperature thresholds that might trigger more rapid retreat or even collapse, with renewed calls to meet the more ambitious target of the Paris Climate Agreement and limit warming to +1.5 °C above pre-industrial. Here we synthesise multiple lines of evidence to show that +1.5 °C is too high and that even current climate forcing (+1.2 °C), if sustained, is likely to generate several metres of sea-level rise over the coming centuries, causing extensive loss and damage to coastal populations and challenging the implementation of adaptation measures. To avoid this requires a global mean temperature that is cooler than present and which we hypothesise to be closer to +1 °C above pre-industrial, possibly even lower, but further work is urgently required to more precisely determine a ‘safe limit’ for ice sheets.

Abstract

Carbon storage in soils is important in regulating atmospheric carbon dioxide (CO2). However, the sensitivity of the soil-carbon turnover time (τsoil) to temperature and hydrology forcing is not fully understood. Here, we use radiocarbon dating of plant-derived lipids in conjunction with reconstructions of temperature and rainfall from an eastern Mediterranean sediment core receiving terrigenous material from the Nile River watershed to investigate τsoilin subtropical and tropical areas during the last 18,000 years. We find that τsoil was reduced by an order of magnitude over the last deglaciation and that temperature was the major driver of these changes while the impact of hydroclimate was relatively small. We conclude that increased CO2 efflux from soils into the atmosphere constituted a positive feedback to global warming. However, simulated glacial-to-interglacial changes in a dynamic global vegetation model underestimate our data-based reconstructions of soil-carbon turnover times suggesting that this climate feedback is underestimated.

Abstract

Focusing on predicting anomalously warm temperatures in Europe, this study delves into a coupled mechanism within the North Atlantic ocean. By examining the accumulation of heat in the North Atlantic ocean, we unveil its potential for forecasting extreme European summers several years in advance. Through a novel ensemble selection approach that integrates this mechanism, we evaluate its impact on decadal temperature prediction skill. Our analysis demonstrates significant enhancements in both deterministic and probabilistic predictions of Central European summer temperature extremes over multiple lead years. These findings underscore the value of incorporating sub‐decadal oceanic processes into climate prediction methodologies, offering critical insights for mitigation strategies against the impacts of anomalous heat events.

Plain Language Summary

The occurrence of extremely warm summers in Europe has increased dramatically in recent years, and this trend is expected to continue as global temperatures rise. These anomalous heat events have significant impacts on society and the economy. It would be very helpful if we could predict these high‐impact events reliably and accurately several years in advance to minimize their potential consequences. In another study, we found that the heat buildup in the North Atlantic ocean plays a crucial role for the prediction skill of anomalously warm European summers. We discovered that the accumulation of heat in the North Atlantic ocean precedes these anomalous events by several years. By using this storage of heat in the North Atlantic ocean, we improve the ability to accurately predict anomalously warm European summers.