Slowing down as an early warning signal for abrupt climate change
Dakos, V. ; Scheffer, M. ; Nes, E.H. van; Brovkin, V. ; Petoukhov, V. ; Held, H. - \ 2008
Proceedings of the National Academy of Sciences of the United States of America 105 (2008)38. - ISSN 0027-8424 - p. 14308 - 14312.
system - thresholds - feedbacks - earth - time
In the Earth's history, periods of relatively stable climate have often been interrupted by sharp transitions to a contrasting state. One explanation for such events of abrupt change is that they happened when the earth system reached a critical tipping point. However, this remains hard to prove for events in the remote past, and it is even more difficult to predict if and when we might reach a tipping point for abrupt climate change in the future. Here, we analyze eight ancient abrupt climate shifts and show that they were all preceded by a characteristic slowing down of the fluctuations starting well before the actual shift. Such slowing down, measured as increased autocorrelation, can be mathematically shown to be a hallmark of tipping points. Therefore, our results imply independent empirical evidence for the idea that past abrupt shifts were associated with the passing of critical thresholds. Because the mechanism causing slowing down is fundamentally inherent to tipping points, it follows that our way to detect slowing down might be used as a universal early warning signal for upcoming catastrophic change. Because tipping points in ecosystems and other complex systems are notoriously hard to predict in other ways, this is a promising perspective.
Global desertification: building a science for dryland development
Reynolds, J.F. ; Smith, D.M.S. ; Lambin, E.F. ; Turner, B.L. ; Mortimore, M. ; Batterbury, S.P.J. ; Downing, T.E. ; Dowlatabadi, H. ; Fernandez, R.J. ; Herrick, J.E. ; Huber-Sannwald, E. ; Jiang, H. ; Leemans, R. ; Lynam, T. ; Maestre, T. ; Ayarza, M. ; Walker, B. - \ 2007
Science 316 (2007)5826. - ISSN 0036-8075 - p. 847 - 851.
sustainability - vulnerability - africa - challenges - feedbacks - knowledge - lessons - ecology - commons - systems
In this millennium, global drylands face a myriad of problems that present tough research, management, and policy challenges. Recent advances in dryland development, however, together with the integrative approaches of global change and sustainability science, suggest that concerns about land degradation, poverty, safeguarding biodiversity, and protecting the culture of 2.5 billion people can be confronted with renewed optimism. We review recent lessons about the functioning of dryland ecosystems and the livelihood systems of their human residents and introduce a new synthetic framework, the Drylands Development Paradigm (DDP). The DDP, supported by a growing and well-documented set of tools for policy and management action, helps navigate the inherent complexity of desertification and dryland development, identifying and synthesizing those factors important to research, management, and policy communities.
On bimodality in warm season soil moisture observations
Teuling, A.J. ; Uijlenhoet, R. ; Troch, P.A.A. - \ 2005
Geophysical Research Letters 32 (2005). - ISSN 0094-8276 - p. L13402 - L13402.
land-atmosphere interactions - leaf-area index - united-states - precipitation - dynamics - drought - climate - transpiration - feedbacks - rainfall
It has recently been suggested that the bimodality in warm season soil moisture observations in Illinois is evidence of a soil moisture-precipitation feedback. Other studies however provide little evidence for a strong feedback in this region. Here we show that seasonality in the meteorological conditions in combination with the non-linearity of the soil moisture response alone can induce this bimodality. The existence of preferred wet and dry soil moisture states may have implications for the understanding and modeling of soil moisture dynamics in mid-latitude regions
More new carbon in the mineral soil of a poplar plantation under Free Air Carbon Erichment (POPFACE): Cause of increased priming effect?
Hoosbeek, M.R. ; Lukac, M. ; Dam, D. ; Godbold, D. ; Velthorst, E.J. ; Bondi, F.A. ; Peressotti, A. ; Cotrufo, M.F. ; Angelis, P. de; Scarascia-Mugnozza, G. - \ 2004
Global Biogeochemical Cycles 18 (2004)1. - ISSN 0886-6236 - 7 p.
elevated atmospheric co2 - organic-matter - terrestrial ecosystems - turnover - forest - storage - system - decomposition - mechanisms - feedbacks
 In order to establish suitability of forest ecosystems for long-term storage of C, it is necessary to characterize the effects of predicted increased atmospheric CO2 levels on the pools and fluxes of C within these systems. Since most C held in terrestrial ecosystems is in the soil, we assessed the influence of Free Air Carbon Enrichment (FACE) treatment on the total soil C content (C-total) and incorporation of litter derived C (C-new) into soil organic matter (SOM) in a fast growing poplar plantation. C-new was estimated by the C3/C4 stable isotope method. C-total contents increased under control and FACE respectively by 12 and 3%, i.e., 484 and 107 gC/m(2), while 704 and 926 gC/m(2) of new carbon was sequestered under control and FACE during the experiment. We conclude that FACE suppressed the increase of C-total and simultaneously increased C-new. We hypothesize that these opposite effects may be caused by a priming effect of the newly incorporated litter, where priming effect is defined as the stimulation of SOM decomposition caused by the addition of labile substrates.