Greenhouse gAs Uk and Global Emissions (GAUGE)

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To minimize the risk of dangerous climate change associated with increasing concentrations of atmospheric greenhouse gases (GHG), as part of ongoing international efforts, the 2008 Climate Change Act requires that the UK reduces its GHG emissions by at least 80% by 2050, compared to 1990 levels. To support such legislation, methods must be developed to reduce uncertainty on existing national GHG emissions estimates and monitor the efficacy of emissions reduction strategies. In 2010, CO2 represented about 85% of total UK GHG emissions, with the remainder largely from methane (CH4) and nitrous oxide (N2O). In 2010, the main UK sources of CO2 were energy supply, road transport, business, and residential; the main sources of CH4 were agriculture and landfill with small sources from gas leakage and coal mines; and the main sources of N2O were agriculture, industrial process, and road transport. There are substantial associated uncertainties with sectoral estimates of these emissions, particularly for N2O.The main focus of Greenhouse gAs Uk and Global Emissions (GAUGE) is to quantify UK budgets of CO2, CH4, and N2O from different sectors, and to improve global GHG budgets. The UK study will focus on fossil fuels and agriculture, the two largest sources of the three GHGs. We will achieve this by combining atmospheric measurements with computer models of the atmosphere, which describe the movement of GHGs after emission. We already have a reasonable idea of where GHGs are emitted but the size of the emissions typically has a large associated error. Depending on the emission type it may also have a substantial seasonal cycle (e.g., agriculture). It is therefore important we make regular GHG measurements at different times of the year and in different places. The UK research aircraft will provide the broad-scale 3-D perspective on the inflow and outflow of UK GHG budgets, complementing information from existing tall towers. The network of tall towers measure GHGs at 100-200m above the surface to ensure that the sampled air is representative of larger areas, and the towers are intentionally sited to provide estimates of GHG emissions in the Devolved Administrations. As part of GAUGE we will add to this network with a tower in the Scottish borders that provides substantially more information about the north of England, Scotland, and the North Sea; a tower over SE England, downwind of London; and we will support existing instruments on the BT tower in central London. The SE London tower and the BT tower together will allow us to provide the first multi-year record of urban emissions from a megacity. We will use GHG isotopes to improve understanding of the fossil fuel sources. A detailed study of agricultural GHG emissions will be conducted over East Anglia, allowing us to quantify the importance of this sector in the UK GHG budget. Weekly measurements aboard a North Sea ferry will provide constraints on UK GHG fluxes by regularly sampling transects of UK outflow. Satellite observations of GHGs offer a unique global perspective, linking UK emissions to the rest of the world, and we will work with NASA to develop and apply new observations to quantify global GHG budgets on a sub-UK spatial scale. Embedded in this long-term measurement strategy will be a measurement intensive to quantify London GHG emissions, where we will use the UK research aircraft to sample profiles of upwind/downwind air, validate dedicated satellite observations, and link urban measurements with downwind in situ and tall tower measurements.In GAUGE we bring together computer models of the atmosphere, and a team of world-leading modellers, in order to relate observed variations of GHGs to estimates of the underlying emissions. Statistical approaches will be used to find emissions that best agree with the measurements, taking account of model and data uncertainties. The main outcome from GAUGE will be robust GHG emission estimates from the UK and from the world.