The burning of biomass (e.g., shrubs, grasslands, trees) has an ongoing role in determining the composition of Earth's surface and atmosphere, and in some regions subsequent emissions of trace gases to the atmosphere rival those from fossil fuel burning. For nearly 40 years the scientific community has studied rates of emissions of trace gases from different types of biomass and associated amospheric gaseous concentrations but our knowledge remains incomplete, reflecting the heterogeneous and stochastic nature of this Earth System process. The advent of space-borne observations of land-surface and tropospheric chemistry provided the first glimpse of the large-scale nature and impact of burning in the global troposphere. These data remain key to scaling-up detailed point- or regional-scale measurements related to burning emissions or associated atmospheric concentrations. However, Earth Observation (EO) data products are difficult to interpret without the aid of computer models of atmospheric chemistry and transport and in situ measurements. In this proposal we have assembled an integrative programme of measurements and modelling of biomass burning that encompasses ground-based and aircraft in situ data, space-borne observations of tropospheric trace gases and particles, and a hierarchy of computer models of atmospheric chemistry (detailed point models to state-of-the-art global 3-D models). Here, we focus on biomass burning over northern boreal regions, with the aircraft missions sampling outflow from North America. Our research focus is to better understand atmospheric chemistry within air masses originating from regions of biomass burning. In particular, we follow up and expand upon surprising results from a recent NERC-funded aircraft campaign (Intercontinental Transport of Ozone and Precursors, ITOP) over the North Atlantic that measured and characterised outflow from the North American boundary layer as it travelled over the North Atlantic towards Europe. During ITOP the aircraft unintentionally sampled outflow from biomass burning and found that models analysing those data were unable to reproduce the large concentrations of organic molecules and the speciation of nitrogen species. As part of this proposal we plan to fly over the North Atlantic specifically to sample outflow from North American biomass burning equipped with a more suitable suite of aircraft instruments that will help to understand and resolve this unexplained discovery in atmospheric chemistry. The resulting data will be analysed by the gold standard Master Chemical Mechanism, an explicit model description of the degradation of relevant atmospheric compounds. One of the biggest challenges that atmospheric scientists typically face is the scaling-up from detailed in situ measurements to regional and larger spatial scales. Here, we address this challenge by using global 3-D models of atmospheric chemistry and transport and data from space-borne sensors by using the model as an intermediary between the aircraft data and the relatively coarse satellite data. By statistically 'tuning' the model using the detailed aircraft data (data assimilation) we can better estimate the magnitude and 3-D distribution of outflow from North American biomass burning and its resulting effects on atmospheric composition over the northern hemisphere. The proposal will provide us with a better fundamental understanding of the evolving atmospheric chemistry within biomass burning, an improved understanding of how to combine data from in situ and space-borne sensors to relate detailed small-scale data to larger spatial scales, and a better quantitative understanding of the impact of boreal forest fires on the atmospheric composition of the northern hemisphere.

PAGODA will focus on the global dimensions of changes in the water cycle in the atmosphere, land, and oceans. The overarching aim is to increase confidence in projections of the changing water cycle on global-to-regional scales through a process-based detection, attribution and prediction. The scientific scope prioritises themes 2,1,3,4 in the AO, adopting a focus on climate processes to extend our understanding of the causes of water source/sink uncertainty at the regional scale, which is where GCMs show huge variations concerning projected changes in precipitation, evaporation, and other water related variables. This model uncertainty is closely linked to shifts in large-scale circulation patterns and surface feedback processes, which differ between models. Furthermore, even where models agree with each other (for example, the suggested trend towards wetter winters and drier summers in Europe, connected to storm tracks and land surface processes), consistency with the real world cannot be taken for granted. The importance of quantitative comparisons between models and observations cannot be overstated: there is opportunity and urgent need for research to understand the processes that are driving changes in the water cycle, on spatial scales that range from global to microscopic, and to establish whether apparent discrepancies are attributable to observational uncertainties, to errors in the specification of forcings, or to model limitations. PAGODA will achieve its scientific objectives by confronting models with observations and reconciling observations, which possess inherent uncertainty and heterogeneity, with robust chains of physical mechanisms - employing model analysis and experiments in an integral way. Detection and attribution is applied throughout, in an iterative fashion, to merge the understanding from observations and models consistently, in order to isolate processes and identify causality. PAGODA is designed to focus specifically on the processes that govern global-to-regional scale changes in the water cycle, particularly on decadal timescales (the timescale of anthropogenic climate change). It addresses processes in the atmosphere, land and oceans, and brings together experts in climate observations, climate models, and detection and attribution. It seeks to exploit important new opportunities for research progress, including new observational data sets (e.g. ocean salinity reanalysis, TRMM and SSMIS satellite products, long precipitation records), new models (HadGEM3 & new capabilities for high resolution simulations), and the new CMIP5 model inter-comparison and to develop new methodologies for process-based detection, attribution and prediction.

The Arctic is undergoing rapid climatic change, with dramatic consequences for the 'Frozen World' (the 'cryosphere'), including reductions in the depth, extent and duration of sea ice, and seasonal snow cover on land, retreat of ice sheets/glaciers, and melting of permafrost ("ground that remains at or below 0 degrees C for at least two consecutive years"). This is important not only for local and regional ecosystems and human communities, but also for the functioning of the entire earth system. Evidence is growing that organic matter frozen in permafrost soils (often for many millennia) is now thawing, making it available for decomposition by soil organisms, with the release of carbon dioxide (CO2) and methane (CH4), both greenhouse gases (GHGs), as by-products. A major concern now is that, because permafrost soils contain 1672 petagrams (1 Pg = 1 billion tonnes) of organic carbon (C), which is about 50% of the total global below-ground pool of organic C, and permafrost underlies ~ 25% (23 million km2) of the N hemisphere land surface, a melting-induced release of GHGs to the atmosphere from permafrost soils could result in a major acceleration of global warming. This is called a 'positive biogeochemical feedback' on global change; in other words, an unintentional side-effect in the global C cycle and climate system. Unfortunately, the interacting biological, chemical and physical controls on CO2 and CH4 emissions from permafrost (and melting permafrost) environments to the atmosphere are the subject of much speculation because the scientific community does not know enough about the interactions between C and water cycling in permafrost systems. Warmer and drier soils may release more CO2, while warmer/wetter soils might release more CH4. Permafrost thawing also causes changes in the way water flows though the landscape (because frozen ground if often impermeable to water), and some areas may become drier, while others wetter. How the relative proportions of CO2 and CH4 emissions change, and their absolute amount, is critical for the overall 'global warming potential' (GWP) because these two gases have different potency as GHGs. Release of C from soils into freshwaters also needs to be taken into account because down-stream 'de-gassing' and decomposition of organic materials also influences releases of CO2 and CH4 from freshwater, or delivery of C to lakes/oceans. All-in-all, predicting the GWP of permafrost regions is scientifically challenging, and the interactions between the water (hydrological) and C cycles are poorly known. In this project we recognise the key role that hydrological processes play in landscape-scale C fluxes in arctic and boreal regions. In permafrost catchments in NW Canada (including areas where permafrost is known to be thawing) we will measure the capture of C from the atmosphere (through photosynthesis), its distribution in plants and soils, and the biological, physical and chemical controls of C transport and delivery from soils to freshwaters, and ultimately to the atmosphere as CO2 and CH4. In essence we wish to 'close the C cycle'. Field-based measurements of key processes in the water and C cycles, including geochemical tracer and state-of-the-art C, hydrogen and oxygen isotope approaches, will be linked by computer modelling. The project team, together with partners in Canada, the US and UK, is in a unique position to link the water and C cycles in permafrost environments, and we will deliver essential scientific knowledge on the potential consequences of climate warming, and permafrost thawing, for GHG emissions from northern high latitudes. Both for local peoples directly dependent on arctic tundra/boreal forest ecosystems for their livelihoods and cultural identity, and for the global community who must respond to, and anticipate, potential consequences of climate and environmental change, this project will represent a significant step forward in understanding/predictive capacity.

The Arctic is undergoing rapid climatic change, with dramatic consequences for the 'Frozen World' (the 'cryosphere'), including reductions in the depth, extent and duration of sea ice, and seasonal snow cover on land, retreat of ice sheets/glaciers, and melting of permafrost ("ground that remains at or below 0 degrees C for at least two consecutive years"). This is important not only for local and regional ecosystems and human communities, but also for the functioning of the entire earth system. Evidence is growing that organic matter frozen in permafrost soils (often for many millennia) is now thawing, making it available for decomposition by soil organisms, with the release of carbon dioxide (CO2) and methane (CH4), both greenhouse gases (GHGs), as by-products. A major concern now is that, because permafrost soils contain 1672 petagrams (1 Pg = 1 billion tonnes) of organic carbon (C), which is about 50% of the total global below-ground pool of organic C, and permafrost underlies ~ 25% (23 million km2) of the N hemisphere land surface, a melting-induced release of GHGs to the atmosphere from permafrost soils could result in a major acceleration of global warming. This is called a 'positive biogeochemical feedback' on global change; in other words, an unintentional side-effect in the global C cycle and climate system. Unfortunately, the interacting biological, chemical and physical controls on CO2 and CH4 emissions from permafrost (and melting permafrost) environments to the atmosphere are the subject of much speculation because the scientific community does not know enough about the interactions between C and water cycling in permafrost systems. Warmer and drier soils may release more CO2, while warmer/wetter soils might release more CH4. Permafrost thawing also causes changes in the way water flows though the landscape (because frozen ground if often impermeable to water), and some areas may become drier, while others wetter. How the relative proportions of CO2 and CH4 emissions change, and their absolute amount, is critical for the overall 'global warming potential' (GWP) because these two gases have different potency as GHGs. Release of C from soils into freshwaters also needs to be taken into account because down-stream 'de-gassing' and decomposition of organic materials also influences releases of CO2 and CH4 from freshwater, or delivery of C to lakes/oceans. All-in-all, predicting the GWP of permafrost regions is scientifically challenging, and the interactions between the water (hydrological) and C cycles are poorly known. In this project we recognise the key role that hydrological processes play in landscape-scale C fluxes in arctic and boreal regions. In permafrost catchments in NW Canada (including areas where permafrost is known to be thawing) we will measure the capture of C from the atmosphere (through photosynthesis), its distribution in plants and soils, and the biological, physical and chemical controls of C transport and delivery from soils to freshwaters, and ultimately to the atmosphere as CO2 and CH4. In essence we wish to 'close the C cycle'. Field-based measurements of key processes in the water and C cycles, including geochemical tracer and state-of-the-art C, hydrogen and oxygen isotope approaches, will be linked by computer modelling. The project team, together with partners in Canada, the US and UK, is in a unique position to link the water and C cycles in permafrost environments, and we will deliver essential scientific knowledge on the potential consequences of climate warming, and permafrost thawing, for GHG emissions from northern high latitudes. Both for local peoples directly dependent on arctic tundra/boreal forest ecosystems for their livelihoods and cultural identity, and for the global community who must respond to, and anticipate, potential consequences of climate and environmental change, this project will represent a significant step forward in understanding/predictive capacity.

Snow is a material with remarkable physical properties that profoundly alters the characteristics of the Earth's surface where it lies. Because snow has a high albedo (the fraction of solar radiation that it reflects rather than absorbs) and a high latent heat of fusion (the energy required to melt it), it delays the warming of the atmosphere and the ground in spring each year. Satellite measurements of Northern Hemisphere snow cover have now been available for 50 years, and a strong decreasing trend correlated with warming has been observed in spring over that period. Less snow accumulates in a warmer climate and melts sooner, increasing the absorption of solar radiation and reinforcing the warming (a strong positive feedback). Snow conducts heat poorly because it contains trapped air and so insulates the ground from cold temperatures in winter; this controls soil freezing and provides protection for short plants, small animals and soil microbes living in snowy regions, with important and complex impacts on the global carbon cycle. For all of these reasons, it is important that climate models should be able to predict snow cover accurately. Unfortunately, the latest climate models still differ greatly in their simulations of how snow cover varies from year to year in the current climate and how it will change in the future. There are many potential sources for this uncertainty, including errors in snowfall and temperature patterns predicted by models, multiple processes that control the rate of snowmelt but may be poorly represented in models, and uncertainty in setting optimal values for model parameters. It has proven very difficult to disentangle these sources of uncertainty and to determine how they can be reduced. In this project, we will use a new modelling system in which a single meteorological variable, model process or parameter value can be varied at a time, allowing highly controlled experiments to precisely determine how they influence simulations. Direct measurements of snow properties at research sites and satellite measurements of snow cover and albedo across the Northern Hemisphere will be used to identify the best simulations. Because snow melts both as the weather warms in spring and as the climate warms, improving the ability of models to simulate the current seasonal cycle and past trends can be expected to improve projections of future conditions, provided that the improvements are obtained for sound physical reasons. Improved predictions and better understanding of the sensitivity of snow to climate change will contribute to reviews of climate science by the Intergovernmental Panel on Climate Change which are essential resources for policymakers. Another important feature of snow is that it stores precipitation that falls in the mountains over winter and releases it in warmer times of year when human demand for water is higher. Many parts of the world are provided with water and threatened by floods from melting snow in upstream mountain regions. Even if the total amount of precipitation does not change in a warming climate, a shift to more falling as rain rather than snow will lead to river flows peaking earlier in the year, requiring major changes in the management of water resources. Global climate models, which cannot resolve processes occurring on scales smaller than a few hundred kilometres, are not adequate tools for informing water management decisions, but national weather services are now beginning to run forecasts for limited areas and short periods with kilometre-scale resolutions. We will use high-resolution meteorological data and the same modelling methods that we applied on the hemispheric scale to make and test predictions for snowmelt in well-instrumented areas of the French and Swiss Alps. Methods developed will be incorporated in a "downscaling toolkit" which will be made available to researchers and water managers by the International Network for Alpine Research Catchment Hydrology.