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The Pliocene, specifically the mid-Piacenzian Warm Period (~3.3-3.0 Ma), is widely referred to as a potential analogue for future climate within the palaeoclimate community. The Pliocene is well placed to be a palaeoclimate analogue given that it is the most recent period of sustained warmth above pre-Industrial levels, and that the atmospheric CO2 concentration is similar-to-modern at ~400 ppmv.Results from the Pliocene Model Intercomparison Project (PlioMIP) highlight similarities in large-scale features of Pliocene climate to the future: global mean surface air temperature is ~3°C warmer and global mean total precipitation is ~7% higher than pre-Industrial. However, it is also important to consider how analogous other factors are, such as the drivers of those changes in climate. Using the outputs from a subset of models in PlioMIP2, we show that less-analogous forcings, such as changes to ice sheets and orography, are responsible for 44% of surface air temperature and sea surface temperature change in the Pliocene, and 49% of precipitation change. These forcings must be taken into consideration, and affect how comparable the climate of the Pliocene is to our warmer future. We discuss the implications of these results, and consider what it means for the Pliocene to be a “palaeoclimate analogue”., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Identifying mechanisms which can guide many-body quantum systems into regimes where properties such as entanglement and long-range coherence are manifest is a fundamental goal for those working in the field of strongly correlated systems. With this comes the potential to realise and exploit states of matter such as superconductors and superfluids, where quantum behaviour is observable at the macroscopic level. In this thesis we study how symmetries and heating can, counterintuively, be used to realise phases of matter with such desirable properties. We prove how heating a many-body system whilst preserving certain symmetries - such as those of the special unitary group - result in the formation of maximum entropy states which are confined to a subspace of the total Hilbert space and are capable of possessing finite, completely uniform off-diagonal correlations. This mechanism is termed heating-induced order and is independent of any microscopic details. We use the Hubbard model as a central example where this mechanism can be observed. Heating is introduced to the system via periodic driving or local dissipation and we study the various ordered steady states which emerge in this setup. We discuss the applicability of this mechanism to the thermodynamic limit and its relevance to recent solid-state experiments observing photo-induced superconductivity in irradiated compounds. We then show how, in an open quantum system, the satisfaction of a set of simple symmetry-based conditions guarantees an absence of stationarity and the formation of coherent oscillations in the long-time limit. We prove how this result subsumes and goes beyond the established notion of a Decoherence Free Subspace. When these conditions are satisfied in the presence of heating-induced order we observe the formation of an entangled, correlated state undergoing identical limit cycles at all positions in space. This leads us to formulate a novel process for quantum synchronisation which is based on the combination of these symmetry-based conditions and the mechanism of heating-induced order.

Palaeoclimate simulations improve our understanding of the climate, inform us about the performance of climate models in a different climate scenario, and help to identify robust features of the climate system. Here, we analyse Arctic warming in an ensemble of 16 simulations of the mid-Pliocene Warm Period (mPWP), derived from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). The PlioMIP2 ensemble simulates Arctic (60–90∘ N) annual mean surface air temperature (SAT) increases of 3.7 to 11.6 ∘C compared to the pre-industrial period, with a multi-model mean (MMM) increase of 7.2 ∘C. The Arctic warming amplification ratio relative to global SAT anomalies in the ensemble ranges from 1.8 to 3.1 (MMM is 2.3). Sea ice extent anomalies range from −3.0 to -10.4×106 km2, with a MMM anomaly of -5.6×106 km2, which constitutes a decrease of 53 % compared to the pre-industrial period. The majority (11 out of 16) of models simulate summer sea-ice-free conditions (≤1×106 km2) in their mPWP simulation. The ensemble tends to underestimate SAT in the Arctic when compared to available reconstructions, although the degree of underestimation varies strongly between the simulations. The simulations with the highest Arctic SAT anomalies tend to match the proxy dataset in its current form better. The ensemble shows some agreement with reconstructions of sea ice, particularly with regard to seasonal sea ice. Large uncertainties limit the confidence that can be placed in the findings and the compatibility of the different proxy datasets. We show that while reducing uncertainties in the reconstructions could decrease the SAT data–model discord substantially, further improvements are likely to be found in enhanced boundary conditions or model physics. Lastly, we compare the Arctic warming in the mPWP to projections of future Arctic warming and find that the PlioMIP2 ensemble simulates greater Arctic amplification than CMIP5 future climate simulations and an increase instead of a decrease in Atlantic Meridional Overturning Circulation (AMOC) strength compared to pre-industrial period. The results highlight the importance of slow feedbacks in equilibrium climate simulations, and that caution must be taken when using simulations of the mPWP as an analogue for future climate change.

The assumption that physical systems relax to a stationary state in the long-time limit underpins statistical physics and much of our intuitive understanding of scientific phenomena. For isolated systems this follows from the eigenstate thermalization hypothesis. When an environment is present the expectation is that all of phase space is explored, eventually leading to stationarity. Notable exceptions are decoherence-free subspaces that have important implications for quantum technologies. These have been studied for systems with a few degrees of freedom only. Here we identify simple and generic conditions for dissipation to prevent a quantum many-body system from ever reaching a stationary state. We go beyond dissipative quantum state engineering approaches towards controllable long-time non-stationary dynamics typically associated with macroscopic complex systems. This coherent and oscillatory evolution constitutes a dissipative version of a quantum time-crystal. We discuss the possibility of engineering such complex dynamics with fermionic ultracold atoms in optical lattices.

The 8.2 ka event is a well-known cooling event in the Northern Hemisphere, but is poorly understood in Madagascar. Here, we compare paleoclimate data and outputs from paleoclimate simulations to better understand it. Records from Madagascar suggest two distinct sub-events (8.3 ka and 8.2 ka), that seem to correlate with records from northern high latitude. This could indicate causal relationships via changes in the Atlantic Meridional Overturning Circulation (AMOC) with changes in moisture source's δ18O, and changes in the mean position of the Inter-Tropical Convergence Zone (ITCZ), as climate modelling suggests. These two sub-events are also apparent in other terrestrial records, but the climatic signals are different. The prominent 8.2 ka sub-event records a clear antiphase relationship between the northern and southern hemisphere monsoons, whereas such relationship is less evident during the first 8.3 ka sub-event. Data–model comparison have also shown a mismatch between the paleoclimate data and the model outputs, the causes of which are more or less understood and may lie in the proxies, in the model, or in both data and model. Knowing that paleoclimate proxies and climate models produce different sets of variables, further research is needed to improve the data–model comparison approach, so that both paleoclimate data and paleoclimate models will better predict the likely climate status of a region during a specified time in the past with minimal uncertainties.

Climate change and the subsequent impact this has on carbon emissions for buildings has shown great concern for the industry. With over 1.35 million non-domestic buildings at least over 25 years old; the need for more practical refurbishment strategies in order to decarbonise and future-proof the old building stock against climate change is vital. The aim of this paper is to explore more sustainable, economic and less-disruptive refurbishment approaches for an air conditioned building as efficient future weather mitigation measures. Particular emphasis was placed on the evaluation of the carbon reductions associated with the best-suited approaches under two future climatic scenarios, 2030 & 2050.\ud \ud A building simulation model of a public office building has been developed to assess the current energy performance as well as the predicted future energy performance for two refurbishment strategies. These strategies are adaptive thermal control and fabric modification. A reduction in carbon emissions, of 7.5%, results from applying adaptive heating and cooling set points to the model with a current weather data scenario. This reduces to 6.8% in 2030 and 5.3% in 2050. The potential savings are most significant for the current climate scenario and then reduce for the 2030 and 2050 scenarios largely because of an elevation in heating set points. In terms of cooling, an upper limit to the cooling set point of 26°C prevents meaningful differentiation between the 2030 and 2050 adaptive cooling set points but is necessary due to the lack of opportunities for building occupants to adapt their conditions. There is scope for research to be carried out into the application of adaptive set points for existing buildings. Some work has been carried out on the cooling scenario but little appears to have been done for heating as of yet. Given that this could be retrofitted into BMS systems, it is a potential option to reduce building carbon emissions with minimal cost for buildings with centralised systems. For the fabric modification, a significant reduction in carbon emissions was achieved by the use of composite panels to replace much of the glazing. This resulted in a significant improvement in building performance but at a significant investment cost.

The early Holocene cooling, which occurred around 8200 calendar years before present, was a prominent abrupt event around the north Atlantic region. Here, we investigate the timing, duration, magnitude and regional coherence of the event as expressed in carbonate oxygen-isotope records from three lakes on northwest Europe's Atlantic margin in western Ireland, namely Loch Avolla, Loch Gealáin and Lough Corrib. An abrupt negative oxygen-isotope excursion lasted about 200 years. Comparison of records from three sites suggests that the excursion was primarily the result of a reduction of the oxygen-isotope values of precipitation, which was likely caused by lowered air temperatures, possibly coupled with a change in atmospheric circulation. Comparison of records from two of the lakes (Loch Avolla and Loch Gealáin), which have differing bathymetries, further suggests a reduction in evaporative loss of lake water during the cooling episode. Comparison of climate model experiments with lake-sediment isotope data indicates that effective moisture may have increased along this part of the northeast Atlantic seaboard during the 8200-year climatic event, as lower evaporation compensated for reduced precipitation.

The early Eocene (~55 to 50 Ma) is a time period which has been explored in a large number of modelling and data studies. Here, using an ensemble of previously published model results, making up "EoMIP" – the Eocene Modelling Intercomparison Project – and syntheses of early Eocene terrestrial and sea surface temperature data, we present a self-consistent inter-model and model–data comparison. This shows that the previous modelling studies exhibit a very wide inter-model variability, but that at high CO2, there is good agreement between models and data for this period, particularly if possible seasonal biases in some of the proxies are considered. An energy balance analysis explores the reasons for the differences between the model results, and suggests that differences in surface albedo feedbacks, water vapour and lapse rate feedbacks, and prescribed aerosol loading are the dominant cause for the different results seen in the models, rather than inconsistencies in other prescribed boundary conditions or differences in cloud feedbacks. The CO2 level which would give optimal early Eocene model–data agreement, based on those models which have carried out simulations with more than one CO2 level, is in the range of 2500 ppmv to 6500 ppmv. Given the spread of model results, tighter bounds on proxy estimates of atmospheric CO2 and temperature during this time period will allow a quantitative assessment of the skill of the models at simulating warm climates. If it is the case that a model which gives a good simulation of the Eocene will also give a good simulation of the future, then such an assessment could be used to produce metrics for weighting future climate predictions.