Climate extremes can negate the expected increase in terrestrial carbon uptake

Markus Reichstein, Michael Bahn, Philippe Ciais, Dorothea Frank, Miguel D. Mahecha, Sonia I. Seneviratne, Jakob Zscheischler, Christian Beer, Nina Buchmann, David C. Frank, Dario Papale, Anja Rammig, Pete Smith, Kirsten Thonicke, Marijn van der Velde, Sara Vicca, Ariane Walz & Martin Wattenbach
Climate extremes and the carbon cycle, Nature 500, 287-295, 2013
Evidence is mounting that climate extremes such as droughts or storms can lead to a decrease in regional ecosystem carbon stocks and therefore have the potential to negate an expected, warming-related increase in terrestrial carbon uptake. Extreme events not only affect the carbon cycle concurrently (for example, by reducing vegetation productivity or destroying carbon stocks during fire events) but can initiate significant lagged responses, for instance, changing soil physical and chemical properties and soil respiration; tree mortality after failing hydraulic transport as a result of drought-derived embolism in tree stems; and weakened resistance to abiotic stress; all these can lead to shifts in plant, microbial and animal species composition. Thus, even a small shift in the frequency or severity of climate extremes could substantially reduce carbon sinks and may result in sizeable positive feedbacks to climate warming. Furthermore, lagged effects in societal and economic systems are possible with substantial lagged responses in the carbon cycle, for example if increasing food prices caused by low yields, combined with risk of wind throw, were to encourage conversion of forests to croplands or grasslands. To obtain reliable estimates of the sign and magnitude of future carbon-cycle feedbacks, we need a better understanding and descriptions of both the occurrence of climate extremes themselves and the ecosystem carbon-cycle processes that are triggered by climate extremes. To this end, we advocate a new generation of ecosystem manipulation experiments dedicated to studying extreme events, targeted long-term carbon-cycle observations, and an emphasis on high-resolution climate and biosphere modelling.

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