This project is designed to determine how much carbon dioxide (CO2) is absorbed by the South Atlantic and neighbouring Southern Ocean, and how important this is in the global picture. We will achieve this by measurement of atmospheric CO2 and related species at several key islands, and on a commercial ship, and by use of the atmospheric data in modelling studies to determine the uptake (amount absorbed) and whether it is changing over time. Understanding the uptake of CO2 by the oceans is essential, if we are to meet the challenge of understanding global warming by greenhouse gases. This is because, of the CO2 we produce by burning fossil fuels, only about half stays in the atmosphere and contributes to global warming. Most of the remainder is taken up by the global oceans, which, while not contributing to global warming, does contribute to the harmful acidification of the oceans. But exactly how much is taken up, in which oceans, and how this uptake might change in a warming climate is unclear. One important region with the least clarity is the South Atlantic Ocean. By determining CO2 uptake of the South Atlantic and neighbouring Southern Ocean, this project will provide new information that will improve models of the global CO2 cycle. Our work will also contribute to answering the question if Southern Ocean CO2 uptake is changing under global warming. If it is, the implications are serious, and will affect future international emissions negotiations. Although CO2 is measured in seawater in the South Atlantic (for example by British Antarctic Survey), there are virtually no measurements of CO2 in the air above the region. This is because the inhabited islands are UK-owned, and the UK does not participate in international efforts to monitor atmospheric CO2, which are coordinated by the UN's Global Atmosphere Watch programme. Measuring CO2 from the atmosphere is perhaps more important, and more revealing, than measuring from the ocean. The reason is that the atmosphere mixes much faster than the ocean, and so measurements from any given station are representative of a region covering hundreds or even thousands of square kilometres, compared to only a few square kilometres for ocean water measurements. Our measurements will assess the differences in CO2 as air blows across the ocean and CO2 is absorbed by the water. CO2 varies greatly across the planet, both by latitude and by season, just as temperature varies. Our measurements will be carried out by a mixture of continuous observations and canister sampling. Continuous measurement of CO2 will be made at Ascension Island, near the equator, and at Falkland Islands, around 50S. CO2 will also be measured by canister sampling at these and three other UK islands. In addition, O2 concentrations and the isotope 13C in CO2 will be measured from the canister samples. Measuring these additional species tells us about the non-photosynthetic CO2, both fossil-fuel emissions and ocean uptake. Finally, we will also measure CO2 and O2 continuously onboard a commercial ship travelling across the Atlantic, to complement the data from the fixed stations. To interpret our measurements, we will carry out modelling studies. Presently, models based on ocean-water measurement seem to give different answers from the models based on the sparse atmospheric data. It is possible that CO2 uptake may change as the oceans warm, but much more evidence is needed. Our modelling studies will address these problems and will provide a much better understanding of how much CO2 is being taken up into the water in the region. Our work will help improve knowledge of one of the most poorly understood parts of the global carbon budget, the Southern Ocean. Better understanding of the atmospheric side of the equation will also be very helpful to oceanographers, because the South Atlantic and neighbouring Southern Ocean are a great global weather factory, and a key turning point of the ocean circulation system.

A new paradigm has emerged in recent years for explaining late Pleistocene glacial-interglacial climate transitions. According to this paradigm, a clear distinction between mechanisms that operate on 'orbital' and on 'millennial' timescales is no longer made. The slow orbital (insolation) pacing of the ice-ages would thus engender strong positive feedbacks, which could themselves emerge on much shorter timescales. Glacial-interglacial fluctuations in atmospheric CO2 are emblematic of this notion; they clearly make an important contribution to glacial-interglacial radiative forcing, but they appear to accrue through rapid changes that are somehow linked with asymmetric inter-hemispheric climate anomalies (the 'bipolar seessaw'). However, not all rapid changes in atmospheric CO2 are associated with glacial-interglacial transitions. This raises the important question of what has controlled millennial CO2 changes in the past, and what (if anything) is special about deglacial versus mid-glacial CO2 pulses. Current data does not allow us to address these questions adequately. What is needed is a new set of high-resolution reconstructions of Southern Ocean up-welling and deep-water ventilation, which can be linked to the ice-core chronology and thus compared with similarly detailed records of abrupt North Atlantic climate variability. This project sets out to provide these reconstructions, and on thus place our understanding of past millennial CO2 variability on a more robust observational footing than has hitherto been possible.

Forecasts of climate rely on model projections, but derivation of sophisticated climate models from first principles is not currently feasible. Therefore, evaluating climate models with observations is essential. The development and improvement of global climate models is currently only based on comparison with and tuning to historical observations of climate (the instrumental record). Model simulations of the present climate are well-tuned and are in general agreement with each other. However, there is no clear relationship between model performance for present day and model behaviour for projections. Models show a range of sensitivities when predicting the future climate response to the emission of greenhouse gases. This indicates that the evaluation of models using observations of historical climate is insufficient. It is very difficult to reduce uncertainties on projections based on the instrumental period only and the use data from earlier periods is critical. A wide variety of different climate states are recorded in the geological record (spanning greenhouse to icehouse scenarios). The modelling of past climates, in combination with data from the geological record, provides a unique laboratory to evaluate the ability of models to forecast global change. While data is available from numerous intervals in Earth history, analysis is often constrained by the availability of material of the correct age and data collection is often very time consuming and expensive (e.g. for marine sediment cores). For this reasons, it is important that data on past climate and environments is utilised optimally and that challenges resulting from sparsity of the data as well as from temporal and spatial uncertainties are addressed in the best way possible. The earth system modelling and proxy reconstruction communities often have little contact with professional statisticians. Even in publications, ad-hoc methods are used instead of established statistical "best practice". If inappropriate statistical methods are used, inference about models and the earth system will be weakly supportable or plainly wrong. To avoid these problems and to realise the opportunity of improved earth system forecasting, sound statistical methods as advised by statisticians must be used. On the other hand, use of appropriate statistical methodology is often made difficult due to sparsity of data or lack of resources, and statisticians are not always aware of the resulting restrictions on the applicability of methods. Statisticians need to develop awareness of the restrictions and requirements caused by the sparsity of palaeoclimate data and the high complexity or climate models. The Past Earth Network will develop a shared, multi-disciplinary vision for addressing the challenges encompassed by the following four network themes. (1) Quantification of error and uncertainty of data: The uncertainties inherent in different forms of climate data must be well-understood. This is particularly challenging for palaeoclimate data, since uncertainties are often large and varied. (2) Quantification of uncertainty in complex models: The uncertainties in the output of the (complex and high-dimensional) models in use must be well-understood. (3) Methodologies which enable robust model-data comparison: Appropriate methods for model-data comparison must be used, taking into account the nature and sparsity of data. (4) Forecasting and future climate projections: This theme synthesizes the results from the first three themes in order to assess and ultimately improve the ability of climate models to forecast climate change. By addressing these four challenges, results produced by the Past Earth Network will help to better understand and reduce the uncertainties in climate forecasts and ultimately will contribute to the development of better climate forecasts.

The Eurasian Boreal region is warming 3 times faster than the global mean making it a priority region for identifying and understanding land-atmosphere-climate interactions and feedbacks. Much of the warming at these high latitudes is driven by short-lived climate pollutants (SLCPs) such as black carbon and ozone. There is a severe paucity of observations of SLCPs over the Eurasian Boreal region presenting a major challenge to improving our understanding. This proposal aims build capability for improving understanding of SLCP budgets and climate feedbacks in the Eurasian high latitudes. This will be achieved through the establishment of a network of European and Russian scientists, and exploitation of existing observations and global model simulations to motivate future large-scale field observation experiments in the Eurasian boreal region. We will leverage existing NERC investment in our ongoing research into European pollution export and evaluation of atmospheric composition in global models to provide scientific impetus and direction for new research priorities. We will build new, and strengthen existing collaborations between a network of researchers across Europe and Russia. By synthesising existing observations and multi-model simulations, we will motivate the requirements for future observations and prioritise processes that require improved understanding. Within our network we will hold a number of workshops to discuss a) existing data synthesis, b) model-observation comparisons, c) future data needs in the Eurasian boreal region, and d) plans for future aircraft field campaigns. In addition, we will make a scoping visit to the Central Aerological Observatory near Moscow, Russia, in order to evaluate the feasibility of different strategies for a joint aircraft campaign, considering issues such as logistics for joint operations and communication, geo-political constraints on aircraft operations, and experimental strategies for joint flying. The overall end-result of this project will be a coherent community of international scientists with a robust knowledge base of deficiencies in our understanding of short-lived climate pollutants, priorities for observations, and a strategy for developing future large-scale observation networks and large-scale field projects in the Eurasian boreal regions.

The proposed project will test the hypothesis that gradual changes in Atlantic Meridional Overturning Circulation (AMOC) -a system of surface and deep ocean currents that exerts a primary control on Earth's climate, led to abrupt shifts in North Atlantic climate during the transition out of the last ice age and into the present warm interglacial (~20,000-10,000 years ago). Greenlandic ice-core records show clear evidence that this period was characterised by major abrupt climate shifts in less than a decade, which have been attributed to changes in the AMOC regime associated with reduced northward surface heat transport in the high-latitude North Atlantic and its deep southward return flow. Critically, the anomalous weakening of the AMOC in the last decades caused by enhanced fluxes of meltwater and ice export from the Arctic in response to Arctic change prompts the question: Is the current decline in AMOC heralding a new phase of abrupt change similar to those recorded in ice cores and ocean sediments, and what is the response time of North Atlantic climate to changes in high-latitude surface and deep ocean circulation? Resolving and quantifying asynchronous changes within the coupled ocean-atmosphere system is hence essential to improve our theoretical understanding of climate processes and predictive capacity of climate models, as well as identifying under which conditions abrupt climate change occurs. ASYNC is an international collaborative project led by the University of Cambridge that will tackle this fundamental problem. The project will avail of unique North Atlantic Ocean sediment records to generate a suite of precisely dated and multidecadally-resolved proxy records of ocean circulation and climate change. ASYNC represents the first targeted effort to compare high resolution North Atlantic proxy records by precisely integrating the underlying timescales in a continuous fashion. The marine records will be synchronised to the Greenland ice-core chronology via independent and continuous reconstructions of globally synchronous variations in the incoming cosmic ray flux using multidecadally-resolved cosmogenic 10Be records from seafloor sediments and published ice cores. The proposed project will result in new cosmogenic 10Be, sea ice, meltwater discharge, and bottom- and surface-water ventilation reconstructions from three North Atlantic marine sediment cores. The palaeoceanographic reconstructions, and in particular the bottom-water ventilation records, which reflect the southward deep component of AMOC, will be directly compared to events recorded in ice-core climate reconstructions from Greenland. Together, ASYNC will result in the first network of continuously synchronised records of atmospheric, oceanic and sea ice change that will resolve the temporal and spatial propagation of North Atlantic ocean perturbations on the climate system across the major climatic transitions that punctuated the last deglaciation (~20,000-10,000 years ago). Results from ASYNC will advance the current understanding of i) the nature and timing of abrupt climate shifts across climate archives, ii) nonlinear responses of AMOC and climate to gradual Greenland Ice Sheet and Arctic sea ice meltwater forcing, and iii) ocean precursors of rapid climate change in the North Atlantic region.