Project > Long Motivation

Motivation of CARBO-Extreme

Currently European terrestrial ecosystems are estimated to act as a net carbon sink soaking up 7-12% of fossil fuel emissions (Janssens et al., 2003). Also globally the terrestrial biosphere is predicted to sequester carbon at least during the first half of the 21st century (IPCC AR4, 2007). Hence, the terrestrial biosphere potentially contributes to the EU climate protection goal of stabilizing CO2 greenhouse gas concentrations such that “dangerous climate change” is avoided, currently defined by a 2°C global warming ‘guardrail’. However, both the duration and future magnitude of the terrestrial carbon sink are highly uncertain (Friedlingstein et al., 2006). While uncertainties exist regarding the response of the terrestrial carbon cycle to gradual increases in greenhouse gas concentrations and changes in climate, so far the impacts of climate variability and weather extremes have not been accounted for in these considerations of the future evolution, and vulnerability, of terrestrial carbon sinks. This is a very critical gap in our assessment, since studies have clearly shown the climate variability and weather extremes may severely affect the terrestrial carbon cycle and undo several years of carbon sink (Knapp et al., 2002; Ciais et al., 2005; Reichstein et al., 2007). The importance of this topic is enhanced by recent evidence and regional climate model applications that predict more intense and frequent extreme weather events such as droughts, heatwaves and heavy precipitation events over Europe during the 21st century (Christensen and Christensen, 2003; Beniston, 2004; Schär et al., 2004; Frei et al., 2006; Seneviratne et al., 2006), indicating that the climate system no longer is in the assumed stationary mode (Milly et al., 2008).

Secondly, but no less important, another crucial unknown in the terrestrial carbon cycle is the response of soil carbon to increasing temperature. There now are strong indications that temperature may not be the most important factor when other factors become limiting, such as water and substrate availability (Davidson and Janssens, 2006; Fontaine et al., 2007). The limited understanding of these relationships has provoked controversial discussions in the literature (Fang et al., 2005; Knorr et al., 2005). Since modelled responses of respiration temperature sensitivity to drought at ecosystem level appear opposite to observations at hourly to annual time-scales (Reichstein et al., 2007b) there clearly is need for more research. This is even more important since, considerable changes in soil carbon stock over last decades have been reported, which may be related to warming (Bellamy et al., 2005; Smith et al., 2007).

It is evident that a plethora of processes at various time scales are involved in the terrestrial carbon response to climate variability. Our understanding and thus ability to predict effects of climate variability and extreme events on the terrestrial C cycle has so far been hampered by too little integration of experimental data. In particular it is important to integrate different observational quantities that yield information at different time-scales of variability, since single data sets do not contain enough information to constrain models across temporal (and spatial) scales (Sacks et al., 2006). In addition, models are usually parameterized with data under normal conditions, resulting in parameterization that may not be valid under extreme conditions. Hence, there is strong need for integrated multi-data-model fusion approaches in the context of carbon cycling from short-term to centennial scales including extreme conditions.

Bellamy PH, Loveland PJ, Bradley RI, Lark RM, Kirk GJD, Carbon losses from all soils across England and Wales 1978–2003. Nature 437, 245–248, 2005. link to publisher

Beniston M, The 2003 heatwave in Europe: a shape of things to come? An analysis based on Swiss climatological data and model simulations. Geophysical Research Letters 31, L02202, 2004. link to publisher

Christensen JH & Christensen OB, Severe summertime flooding in Europe. Nature 421, 805-806, 2003. link to publisher

Ciais P, Reichstein M, Viovy N, Granier A, et al., Europe-wide reduction in primary productivity caused by the heat and drought in 2003, Nature, 437, 529-533, 2005. link to publisher

Davidson EA, Janssens IA, Temperature sensitivity of soil carbon decomposition and feedbacks to climate change. Nature 440, 165-173, 2006. link to publisher

Fang C, Smith P, Moncrieff JB, Smith JU, Similar response of labile and resistant soil organic matter pools to changes in temperature. Nature 433, 57-59, 2005. link to publisher

Fontaine S, et al., Stability of organic carbon in deep soil layers controlled by fresh carbon supply. Nature 450, 277-281, 2007. link to publisher

Frei C, Schöll R, Fukutome S, et al., Future change of precipitation extremes in Europe: Intercomparison of scenarios from regional climate models. Journal of Geophysical Research 111, D06105, 2006. link to publisher

Friedlingstein P, Bopp L, Rayner P, et al., 2006, Climate-carbon cycle feedback analysis, results from the C4MIP model intercomparison. Journal of Climate 19(14), 3337–3353, 2006. link to publisher

Janssens IA, Freibauer A, Ciais P, et al., Europe's terrestrial biosphere absorbs 7 to 12% of European anthropogenic CO2 emissions. Science 300, 1538-1542, 2003. link to publisher

Knapp AK, Fay PA, Blair JM, et al., Rainfall variability, carbon cycling, and plant species diversity in a mesic grassland. Science 298, 2202-2205, 2002. link to publisher

Knorr W, Prentice IC, House JI, Holland EA, Long-term sensitivity of soil carbon turnover to warming., Nature 433, 298-301, 2006. link to publisher

Milly PCD, Betancourt J, Falkenmark M, et al., Stationarity Is Dead: Whither Water Management? Science 319(5863), 573 - 574, 2008. link to publisher

Reichstein M, Ciais P, Papale D, et al., Reduction of ecosystem productivity and respiration during the European summer 2003 climate anomaly: a joint flux tower, remote sensing and modelling analysis. Global Change Biology 13, 634–651, 2007(a). link to publisher

Reichstein M, Papale D, Valentini R, et al., Determinants of terrestrial ecosystem carbon balance inferred from European eddy covariance flux sites. Geophysical Research Letters, 34, L01402, 2007(b). link to publisher \\\

[-Sacks WJ, Schimel DS, Monson RK, Braswell BH, '''Model-data synthesis of diurnal and seasonal CO2 fluxes at Niwot Ridge, Colorado.''' Global Change Biology, 12, 240-259, 2006. link to publisher-] \\\

Schär C, Vidale PL, Lüthi D, et al., The role of increasing temperature variability in European summer heatwaves. Nature 427, 332-336, 2004. link to publisher \\\

Seneviratne SI, Lüthi D, Litschi M, et al., Land-atmosphere coupling and climate change in Europe. Nature 443, 205-209, 2006. link to publisher

Smith, P, Chapman SJ, Scott WA, et al., Climate change cannot be entirely responsible for soil carbon loss observed in England and Wales, 1978- 2003. Global Change Biology, 13, 2605-2609, 2007. link to publisher