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Confident knowledge of past atmospheric CO2 levels is fundamental to our understanding of the drivers of past climate changes, evolutionary transitions and extinctions, and the sensitivity of our climate system to past, present and future carbon emissions. Over the past few years, a team of terrestrial and marine paleo-CO2 proxy experts has collaborated to compile published paleo-CO2 reconstructions and develop a dedicated database. Vetting and categorizing these data in the light of current proxy understanding has led to a much-refined Cenozoic CO2 record that covaries with independent climate estimates such as temperature, sea level and the evolution of C4 grasses. This refined CO2 record provides a reliable reference for climate scientists and modelers who aim to compare their data to or drive their models with paleo-CO2 information. However, significant data gaps remain to be filled and further proxy development and data intercomparison are essential to improve these reconstructions and establish a rigorous and reliable record of paleo-CO2. I will report on these efforts and provide some examples of marine carbonate chemistry perturbations across the Cenozoic.

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Ocean life is on the front lines of climate change, with marine ectotherms living closer to their upper thermal limits and shifting their distributions faster than species on land. Marine communities are also rapidly turning over to new species compositions. I will discuss how large-scale observations are transforming our understanding of climate impacts on ocean life, some of the unique conservation challenges these dynamics create, and potential adaptation solutions.

Sea-level rise will significantly alter coasts and associated ecosystems, such as mangroves and tidal marshes. Palaeoecological evidence and model projections suggest that inundation and erosion will increasingly dominate shoreline processes, impacting the extent and condition of coastal ecosystems. Observational data indicate that these ecosystems have some capacity to adapt to the changing conditions imposed by sea-level rise. Critical factors include sediment supply and vegetation productivity, which contribute to vertical growth of substrates. These processes underpin a positive relationship between inundation and vertical accretion that creates negative feedback under conditions of rising sea levels and contributes to coastal ecosystem and shoreline resilience.

Applying this feedback relationship, inundation and sedimentation are lowest at the landward margin of coastal ecosystems. Lateral expansion of inundation with sea-level rise is inevitable at the landward margin, only hindered by tidal obstructions from infrastructure, engineering structures (e.g., ditches, levees, and drains), and steep slopes that restrict tidal ingress and squeeze coastal ecosystems between land and sea. Conversely, at the seaward margin, where inundation frequency is higher, enhanced sedimentation aids vertical adjustment, while erosion may alter the lateral extent. Focusing on the dynamics of these margins, anticipated shoreline changes under varying conditions of sea-level rise and sedimentation can be classified.

Efforts to validate these predicted change classes using dense spatio-temporal data from the Landsat archive highlight the influence of sea-level rise and other climatic phenomena on coastal ecosystem condition and extent. Chenier and bars arising from storms and cyclones, and formation of beach ridges and spits associated with wave action modulate coastal ecosystem extent and condition. This may variably improve resilience to sea-level rise by providing a sediment subsidy or attenuate inundation; or reduce condition by causing erosion or impoundment of tidal waters. Climatic phenomena, such as ENSO, which affects temperature, precipitation, and tides, are implicated in widespread coastal ecosystem dieback. Concurrent drought conditions and extreme fire weather have caused unprecedented fire damage to coastal ecosystems and death of vegetation, raising concerns that compounding of climate change processes will restrict the negative feedback that underpins the resilience of coastal ecosystems. Monitoring coastal ecosystems using satellite technology can provide near real-time capability to identify declining conditions and could support early warning systems that guide actions to enhance resilience.

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