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Publication - Dr Natalie Lord

    An impulse response function for the "long tail" of excess atmospheric CO2 in an Earth system model


    Lord, NS, Ridgwell, AJ, Thorne, MC & Lunt, DJ, 2016, ‘An impulse response function for the "long tail" of excess atmospheric CO2 in an Earth system model’. Global Biogeochemical Cycles, vol 30., pp. 2-17


    The ultimate fate of (fossil fuel) CO2 emitted to the
    atmosphere is governed by a range of sedimentological and geological
    processes operating on timescales of up to the ca. hundred thousand year
    response of the silicate weathering feedback. However, how the various
    geological CO2 sinks might saturate and feedbacks weaken in
    response to increasing total emissions is poorly known. Here we explore
    the relative importance and timescales of these processes using a 3-D
    ocean-based Earth system model. We first generate an ensemble of 1 Myr
    duration CO2 decay curves spanning cumulative emissions of up
    to 20,000 Pg C. To aid characterization and understanding of the model
    response to increasing emission size, we then generate an impulse
    response function description for the long-term fate of CO2
    in the model. In terms of the process of carbonate weathering and
    burial, our analysis is consistent with a progressively increasing
    fraction of total emissions that are removed from the atmosphere as
    emissions increase, due to the ocean carbon sink becoming saturated,
    together with a lengthening of the timescale of removal from the
    atmosphere. However, we find that in our model the ultimate CO2
    sink—silicate weathering feedback—is approximately invariant with
    respect to cumulative emissions, both in terms of its importance (it
    removes the remaining excess ~7% of total emissions from the atmosphere)
    and timescale (~270 kyr). Because a simple pulse-response description
    leads to initially large predictive errors for a realistic time-varying
    carbon release, we also develop a convolution-based description of
    atmospheric CO2 decay which can be used as a simple and efficient means of making long-term carbon cycle perturbation projections.

    Full details in the University publications repository