Huntingford Chris

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Huntingford
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Chris
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  • Article
    Recent trends and drivers of regional sources and sinks of carbon dioxide
    (Copernicus Publications on behalf of the European Geosciences Union, 2015-02-02) Sitch, Stephen ; Friedlingstein, Pierre ; Gruber, Nicolas ; Jones, S. D. ; Murray-Tortarolo, G. ; Ahlstrom, Andreas P. ; Doney, Scott C. ; Graven, Heather ; Heinze, Christoph ; Huntingford, Chris ; Levis, Samuel ; Levy, Peter E. ; Lomas, Mark ; Poulter, Benjamin ; Viovy, Nicolas ; Zaehle, Sonke ; Zeng, Ning ; Arneth, Almut ; Bonan, Gordon B. ; Bopp, Laurent ; Canadell, Josep G. ; Chevallier, Frédéric ; Ciais, Philippe ; Ellis, Richard ; Gloor, Emanuel ; Peylin, Philippe ; Piao, S. L. ; Le Quere, Corinne ; Smith, Benjamin ; Zhu, Zaichun ; Myneni, Ranga
    The land and ocean absorb on average just over half of the anthropogenic emissions of carbon dioxide (CO2) every year. These CO2 "sinks" are modulated by climate change and variability. Here we use a suite of nine dynamic global vegetation models (DGVMs) and four ocean biogeochemical general circulation models (OBGCMs) to estimate trends driven by global and regional climate and atmospheric CO2 in land and oceanic CO2 exchanges with the atmosphere over the period 1990–2009, to attribute these trends to underlying processes in the models, and to quantify the uncertainty and level of inter-model agreement. The models were forced with reconstructed climate fields and observed global atmospheric CO2; land use and land cover changes are not included for the DGVMs. Over the period 1990–2009, the DGVMs simulate a mean global land carbon sink of −2.4 ± 0.7 Pg C yr−1 with a small significant trend of −0.06 ± 0.03 Pg C yr−2 (increasing sink). Over the more limited period 1990–2004, the ocean models simulate a mean ocean sink of −2.2 ± 0.2 Pg C yr−1 with a trend in the net C uptake that is indistinguishable from zero (−0.01 ± 0.02 Pg C yr−2). The two ocean models that extended the simulations until 2009 suggest a slightly stronger, but still small, trend of −0.02 ± 0.01 Pg C yr−2. Trends from land and ocean models compare favourably to the land greenness trends from remote sensing, atmospheric inversion results, and the residual land sink required to close the global carbon budget. Trends in the land sink are driven by increasing net primary production (NPP), whose statistically significant trend of 0.22 ± 0.08 Pg C yr−2 exceeds a significant trend in heterotrophic respiration of 0.16 ± 0.05 Pg C yr−2 – primarily as a consequence of widespread CO2 fertilisation of plant production. Most of the land-based trend in simulated net carbon uptake originates from natural ecosystems in the tropics (−0.04 ± 0.01 Pg C yr−2), with almost no trend over the northern land region, where recent warming and reduced rainfall offsets the positive impact of elevated atmospheric CO2 and changes in growing season length on carbon storage. The small uptake trend in the ocean models emerges because climate variability and change, and in particular increasing sea surface temperatures, tend to counter\-act the trend in ocean uptake driven by the increase in atmospheric CO2. Large uncertainty remains in the magnitude and sign of modelled carbon trends in several regions, as well as regarding the influence of land use and land cover changes on regional trends.
  • Article
    Implications of improved representations of plant respiration in a changing climate
    (Nature Publishing Group, 2017-11-17) Huntingford, Chris ; Atkin, Owen K. ; Martinez-de la Torre, Alberto ; Mercado, Lina M. ; Heskel, Mary ; Harper, Anna B. ; Bloomfield, Keith J. ; O'Sullivan, Odhran S. ; Reich, Peter B. ; Wythers, Kirk R. ; Butler, Ethan E. ; Chen, Ming ; Griffin, Kevin L. ; Meir, Patrick ; Tjoelker, Mark ; Turnbull, Matthew H. ; Sitch, Stephen ; Wiltshire, Andrew J. ; Malhi, Yadvinder
    Land-atmosphere exchanges influence atmospheric CO2. Emphasis has been on describing photosynthetic CO2 uptake, but less on respiration losses. New global datasets describe upper canopy dark respiration (Rd) and temperature dependencies. This allows characterisation of baseline Rd, instantaneous temperature responses and longer-term thermal acclimation effects. Here we show the global implications of these parameterisations with a global gridded land model. This model aggregates Rd to whole-plant respiration Rp, driven with meteorological forcings spanning uncertainty across climate change models. For pre-industrial estimates, new baseline Rd increases Rp and especially in the tropics. Compared to new baseline, revised instantaneous response decreases Rp for mid-latitudes, while acclimation lowers this for the tropics with increases elsewhere. Under global warming, new Rd estimates amplify modelled respiration increases, although partially lowered by acclimation. Future measurements will refine how Rd aggregates to whole-plant respiration. Our analysis suggests Rp could be around 30% higher than existing estimates.