Greenhouse Gas Emissions & Feedbacks

Flux tower

Tower for measuring carbon flux in Barbeau, France. Copyright CNRS Jean-Yves Pontailler.

To quantify the influence of man-made greenhouse gases (GHGs) on recent and future climate, it is essential to quantify their sources and sinks, including both anthropogenic emissions and the response of natural sources and sinks to changing environmental conditions.

However, inconsistencies currently exist between the budget estimates for some gases, and there is a poor understanding of the impacts of land use on GHG emissions and the effects of climate change on terrestrial and marine carbon sinks. These factors are major sources of uncertainty in predicting climate change.

To address these scientific uncertainties, NERC is investing £8·1 million into a five-year Greenhouse Gas Emissions & Feedbacks research programme.

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To quantify the influence of man-made greenhouse gases (GHGs) on recent and future climate it is essential to quantify their sources and sinks. This includes both direct anthropogenic emissions and the responses of natural sources and sinks to changing environmental conditions.

Estimating emissions on national and even sub-national scales is important, both to quantify the impact of possible interventions (eg waste disposal methods to reduce methane emissions), and to enable administrations to know whether they are meeting statutory emissions targets.

However, for some gases, current top-down budget estimates are not consistent with bottom-up emission inventories, pointing to a key research gap. Further, there is currently very poor understanding of the impacts of drivers such as land use on GHG emissions, while the feedbacks from climate change itself on terrestrial and marine carbon sinks are also poorly known. These factors are major sources of uncertainty in predicting future climate change in response to a variety of policy options.

This programme focuses on the three major anthropogenic GHGs not regulated by the Montreal Protocol: carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Together these accounted for around 87% of the radiative forcing of the atmosphere by long-lived greenhouse gases in 2005.[1]

Currently three approaches are available to estimate GHG sources and sinks:

  1. Inventories and process studies
    Emissions of anthropogenic GHGs can be estimated from socioeconomic data; eg power station output, cattle numbers, fertiliser application. Such inventories are sometimes supported by detailed field studies of particular processes.

    Inventories have the advantage that they can provide high spatio-temporal resolution and disaggregation of emissions by sector. However, the upscaling of field studies to national scale is highly problematic.

    Inventory methodology is an active area of largely non-environmental science research, supported by a number of initiatives.[2]

  2. Regional inversions based on boundary layer GHG observations
    Direct measurements of atmospheric GHG concentrations from towers are combined with high resolution regional weather models to determine the trajectories along which the GHGs have travelled to reach the detector.

    By combining data observed over a wide range of wind/weather regimes a picture of sources is built up. This method has the potential to deliver high spatial resolution (dependent on the observing network), but is sensitive to estimates of the background concentrations in unpolluted air, and may be subject to bias if particular sources operate differently in different weather types.

    It is not capable of distinguishing sources from different economic sectors; however in principle improved spatio-temporal resolution could deliver useful sector information.

  3. Global inversions based on EO data and global models
    Satellite GHG observations are assimilated into global weather models to obtain a self-consistent estimate of sources/sinks and atmospheric transports.

    The global coverage of these methods makes them attractive for verifying international emissions protocols and for constraining the poorly-known feedbacks between climate and terrestrial GHG emissions.[3] However, they are still at an early stage of development.

    Satellite retrievals do not give information about boundary layer concentrations (where much of the information about sources resides); limited boundary layer resolution makes it difficult to incorporate data from boundary layer towers; and results are highly sensitive to the underlying land surface model and its (poorly-characterised) errors.

    The ocean is treated as a fixed source/sink term, despite recent evidence of strong interannual variability and potential sensitivity to climate change.[4]

    The Monitoring Atmospheric Composition & Climate (MACC) system, run at ECMWF, is being developed as a (currently pre-) operational service for Europe, under EU funding. It produces estimates of GHG emissions and concentrations with a six-month lag on real time (as well as other aspects of atmospheric composition in near-real time). The system now runs routinely, but the value of its output at this stage is limited by the scientific constraints noted above.

Given the state of development of these methods, it is perhaps not surprising that emissions estimates made using different techniques sometimes disagree substantially.

The goal of this programme is to deliver improvements to the 'top down' methods b and c, and to integrate knowledge from all three methods to deliver improved GHG inventories and predictions for the UK, and for the globe at a regional scale.

A further key output is to define the requirements for a sustained UK GHG observing network that will meet requirements both for monitoring/policy purposes and for ongoing research.

  1. The Intergovernmental Panel on Climate Change: Fourth Assessment Report, 2007.
  2. Eg Defra's GHG R&D platform (PDF, 24KB) - external link, funded at £12·6 million.
  3. The Intergovernmental Panel on Climate Change: Fourth Assessment Report, 2007.
  4. Watson et al - Science 326, 1391-1393 (2009).


2011 - 2016

Can I apply for a grant?

No, not at this time. All proposals have been funded.


This programme has a budget of £8·1 million over 5 years.

Programmes awards

Award details are shown in our online grants browser - Grants on the Web.

View details of funded applications - external link

The following documents and links are related to or give more information about this programme.

Town meeting presentations

DECC presentation (PDF, 1.5MB)

Defra presentation (PDF, 563KB)

ECMWF presentation (PDF, 1.8MB)