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The Anthropocene, global change and sleeping giants: where on Earth are we going?

DOI: 10.1186/1750-0680-1-3

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Although a very important exercise, this approach to defining dangerous climate change can itself be dangerous, in particular because it often ignores the systemic nature of the global environment. Feedbacks and nonlinearities are the rule, not the exception, in the functioning of the Earth System [2], and in this Anthropocene era, where human activities have become a global geophysical force in their own right, there is no doubt that surprises await those who apply linear logic to the climate problem. The carbon cycle is centrally involved in many of these feedbacks and nonlinearities.Here we briefly review several of the more important so-called "sleeping giants" in the carbon cycle, processes that have the potential to accelerate the rate of warming beyond that attributed to human emissions of greenhouse gases [3]. The first of these is based on the impact on soil respiration of rising temperature and changing soil moisture, an example of a response of ecosystem physiology to climate change. Although there is still debate about the magnitude of the increase in soil respiration with temperature, and whether there are compensating effects of enhanced plant growth due to mobilisation of nitrogen in the process, the general consensus is that increasing temperature will cause an increase in the emission of CO2 from soil carbon [4].A second "sleeping giant" is the increase in disturbance in terrestrial ecosystems, often associated with pulses of carbon to the atmosphere. The most notable of these are wildfires and pest outbreaks, both sensitive to both warming and changes in the moisture regime. Although these are natural phenomena in the dynamics of terrestrial ecosystems, an increase in the frequency or extent of these disturbances results in a net loss of carbon to the atmosphere. Observations of the large areas of boreal forest in the northern high latitudes suggest that over the past couple of decades, these forests have experienced enhanced rates and/or areas of


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