Rapid and deep reductions in greenhouse gas emissions are necessary to limit the harm to people around the world expected due to climate change over the 21st Century (IPCC, 2022). However, increasing awareness of the failure of global climate policy to bring about the rate of change in the global economic system necessary to meet the 1.5°C global warming level (van de Ven et al., 2023; UN Environment Programme, 2022;Sognnaes et al., 2021) identified in the Paris Agreement (UNFCCC, 2015) has led some to consider the use of solar geoengineering-the deliberate cooling of the planet by reflecting away incoming sunlight-to reduce these harms (National Academies of Sciences, Engineering, and Medicine, 2021). Such consideration has been made more urgent by the large changes in the climate system already observed at 1.1°C of warming (Gulev et al., 2021), changes which are particularly stark in the polar regions (Pörtner et al., 2019). Recent work has demonstrated the significant risk that several cryospheric tipping elements in the Earth system, including abrupt boreal permafrost thaw, and collapse of the West Antarctic Ice Sheet, may become active at global temperatures below the Paris
<p>The atmospheric boundary layer in the Arctic winter is characterised by strong and long-lived low level stability which arises from long-wave radiative cooling of the surface during the polar night. This atmospheric temperature inversion is a necessary condition for the positive lapse rate feedback, which is a major contributor to Arctic Amplification. In this study, we assess the low-level stability of the winter-time Arctic boundary layer using ground-based and radiosonde observations collected during the MOSAiC (2019-2020) and SHEBA (1997-1998) expeditions, and from Soviet drifting stations (1955-1991). We compare these observations with the representation of Arctic boundary layer stability in models participating in the latest phase of the Coupled Model Intercomparison Project (CMIP6). The observations show a bimodal distribution of clear and cloudy states which has been reported previously. In the clear state, longwave radiative cooling from the surface leads to strong inversions and a stably stratified boundary layer. Whereas, in the cloudy state, inversions are weaker and not confined to the surface. Previous work has shown that many CMIP5-era climate models fail to realistically represent the cloudy state and often overestimate low-level stability. Here, we assess the extent to which the CMIP6 models also show such biases and examine the representation of surface net longwave radiation and turbulent heat fluxes as potential sources of the biases. Finally, we show that across CMIP6 models, low level stability over sea-ice is correlated with inter-model variation in Arctic amplification.</p>
Abstract. The Arctic is warming at almost four times the global average rate. Here we reframe this amplified Arctic warming in terms of global climate ambition to show that it causes a breach of the Paris Agreement’s 1.5 °C and 2 °C limits 5 and 8 years earlier, respectively. This outsized influence on global climate targets highlights the need for better modelling and monitoring of Arctic change.
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