Previous studies on future scenarios identified two key effects of increasing CO2 on the African summer monsoon (ASM): Rising CO2 leads to an enhancement in moisture supply, favoring an increase in ASM precipitation (the thermodynamic effect). However, it also results in a weakening in mean atmospheric flow, thus facilitating a dryness across the ASM region (the dynamic effect). Therefore, the ultimate change in ASM precipitation stems from the balance of both the thermodynamic and dynamic effects. This study further examines the impact of rising CO2 on ASM rainfall, by taking into account various climate states. Our results suggest that an increase in CO2 during warm interglacial periods has a stronger influence from thermodynamic factors than from dynamic factors, resulting in an enhancement in ASM rainfall. In contrast, if CO2 increases under cold glacial climate backgrounds, its dynamic impact dominates a reduction of rainfall in the ASM region.

Warm airmass intrusions (WAIs) from the mid-latitudes significantly impact the Arctic water budget. Here, we combine water vapor isotopes measurements from the MOSAiC expedition, with a Lagrangian-based process attribution diagnostic to track moisture origin and transformation in the central Arctic Ocean during two WAIs, under contrasting sea-ice concentrations (SIC). During winter with high SIC, two moisture states emerge: the local in-Arctic moisture, for which the isotope signal is influenced by kinetic processes in ice-cloud formation, is rapidly overprinted by low-latitude moisture advected poleward during WAI. In summer under low SIC, moisture is supplied through evaporation from land and ocean, with moisture distillation via liquid-cloud formation. The isotopic composition reflects the influence of higher humidity at the evaporation sites. Given the projected increase of frequency and duration of WAIs, our study contributes to assess process changes in the Arctic water cycle.

Due to an imbalance of incoming and outgoing radiation at the top of the atmosphere, excess heat has been accumulating in Earth’s climate system in recent decades, driving global warming and climatic changes. To date it has not been quantified how much of this excess heat is being used for the melting of ground ice in the terrestrial permafrost region. Here, we diagnose changes in sensible and latent heat contents in the northern terrestrial permafrost region from ensemble simulations of a numerical permafrost model. We find that about 3.9 (+1.5|-1.7) ZJ of heat, of which 1.7 (+1.4|-1.5) ZJ (45%) were used to melt ground ice, were taken up by permafrost from 1980 to 2018. This suggests that permafrost is a persistent heat sink similar in magnitude to other components of the cryosphere that requires an explicit consideration in assessments of the Earth’s energy imbalance.