Evaluating heat extremes in the UK Climate Projections (UKCP18)

In recent years, UK summer heatwaves have resulted in thousands of excess deaths, with both extreme temperatures and high humidity increasing health risks. Here, the UK Climate Projections 2018 (UKCP18) are compared to observational (HadUK-Grid) and reanalysis data (ERA5) to quantify model performance at capturing mean, extremes (95th to 99.5th percentiles) and variability in the climate state and heat stress metrics (simplified wet bulb global temperature, sWBGT; Humidex; apparent temperature). Simulations carried out for UKCP18 generally perform as well as or better than CMIP5 models in reproducing observed spatial patterns of UK climate relating to extreme heat, with RMSE values on average ~30% less than for the CMIP5 models. Increasing spatial resolution in UKCP18 simulations is shown to yield a minor improvement in model performance (RMSE values on average ~5% less) compared to observations, however there is considerable variability between ensemble members within resolution classes. For both UKCP18 and CMIP5 models, model error in capturing characteristics of extreme heat generally reduces when using heat stress metrics with a larger vapour pressure component, such as sWBGT. Finally, the 95th percentile of observed UK summer temperature is shown to have ~60% greater interannual variability than the summer mean over the recent past (1981–2000). This effect is underestimated in UKCP18 models (~33%) compared to HadUK-grid and ERA5. Compared to projected future changes in the global mean temperature, UK summer mean and 95th percentile temperatures are shown in increase at a faster rate than the global mean

The biological carbon pump in CMIP6 models: 21st century trends and uncertainties

The biological carbon pump (BCP) stores ∼1,700 Pg C from the atmosphere in the ocean interior, but the magnitude and direction of future changes in carbon sequestration by the BCP are uncertain. We quantify global trends in export production, sinking organic carbon fluxes, and sequestered carbon in the latest Coupled Model Intercomparison Project Phase 6 (CMIP6) future projections, finding a consistent 19 to 48 Pg C increase in carbon sequestration over the 21st century for the SSP3-7.0 scenario, equivalent to 5 to 17% of the total increase of carbon in the ocean by 2100. This is in contrast to a global decrease in export production of –0.15 to –1.44 Pg C y–1. However, there is significant uncertainty in the modeled future fluxes of organic carbon to the deep ocean associated with a range of different processes resolved across models. We demonstrate that organic carbon fluxes at 1,000 m are a good predictor of long-term carbon sequestration and suggest this is an important metric of the BCP that should be prioritized in future model studies

The Bristol CMIP6 Data Hackathon

This is the final version. Available on open access from Wiley via the DOI in this recordThe Bristol CMIP6 Data Hackathon formed part of the Met Office Climate Data Challenge Hackathon series during 2021, bringing together around 100 UK early career researchers from a wide range of environmental disciplines. The purpose was to interrogate the under-utilised but currently most advanced climate model inter-comparison project datasets to develop new research ideas, create new networks and outreach opportunities in the lead up to COP26. Experts in different science fields, supported by a core team of scientists and data specialists at Bristol, had the unique opportunity to explore together interdisciplinary environmental topics summarised in this article

Extinction intensity during Ordovician and Cenozoic glaciations explained by cooling and palaeogeography

A striking feature of the marine fossil record is the variable intensity of extinction during superficially similar climate transitions. Here we combine climate models and species trait simulations to explore the degree to which differing paleogeographic boundary conditions and differing magnitudes of cooling and glaciation can explain the relative intensity of marine extinction during greenhouse-icehouse transitions in the Late Ordovician and the Cenozoic. Simulations modelled the response of virtual species to cooling climate using a spatially explicit cellular automaton algorithm. We find that paleogeography alone may be a minor contributing factor, as identical changes in meridional sea surface temperature gradients caused greater extinction in Late Ordovician simulations than in Cenozoic simulations. Differences in extinction from paleogeography are significant but by themselves insufficient to explain observed differences in extinction intensity. However, when simulations included inferred changes in continental flooding and interval-specific models of sea surface temperature, predicted differences in relative extinction intensity were more consistent with observations from the fossil record. Our results support the hypothesis that intense extinction in the Late Ordovician is partially attributable to exceptionally rapid and severe cooling compared to Cenozoic events