Global Change (and Climate Change)
Mateo Aguado
Over recent decades scientists have provided increasingly solid certainties regarding how human activity is deeply affecting most of the processes that determine the global functioning of the Earth System (Steffen et al., 2005; Duarte et al., 2009; Rockström et al., 2009). This ensemble of human-induced environmental changes are known as global change or global environmental change (Vitousek, 1994). This comprises all human actions whose effects, despite being performed locally, transcend the local or regional scale and impact the structure and overall functioning of the planet (Steffen et al., 2005; Duarte et al., 2009).
As well as the global nature of the current process of change, two features characterise this unique moment of environmental alterations in the Earth’s history: the celerity and intensity with which it is happening, and the fact that just one single species, Homo sapiens, is their main driver (Steffen et al., 2005; Duarte et al., 2009). This trait has led many researchers to call for a modification to the international chronostratigraphic chart (or geological time scale), concluding the Holocene and suggesting the beginning of a new geochronological unit characterised by the anthropic alteration of the global functioning of the Earth System: the Anthropocene.
Within these coordinates, the term global change is used to refer both to the biophysical and the socioeconomic changes affecting the structure and functioning of the Earth System, that include -among many others- alterations to land uses and cover, atmospheric composition, river flows, nitrogen, phosphorous and carbon cycles, marine food chains, biological diversity, human population, use of resources, energy consumption, transportation, communications, etc. (Steffen et al., 2005). Global change, therefore, is much more than the current anthropogenic climate change, and its scope and complexity are only now beginning to be understood (Vitousek, 1994; Steffen et al., 2005).
This two-fold biophysical and socioeconomic dimension of global change allows us to distinguish two major drivers of change: 1) direct drivers, encompassing all factors induced by human beings that directly alter ecosystems’ structure and functioning, such as land-use changes, human-induced climate change, water, soil and air pollution, biological invasions, changes in biogeochemical cycles or the over-exploitation of the biosphere’s biotic and geotic components; and 2) indirect drivers, comprising all sociopolitical factors and processes acting in a diffuse manner, altering ecosystems by acting on one or more direct drivers of change, such as demographic, economic, sociopolitical, cultural or scientific-technological elements (Nelson, 2005; MA, 2005).
Interactions and links among the various drivers of change likewise form part of global change, and may acquire equal or greater importance than each individual change (Steffen et al., 2005). For example, a relatively gradual loss of annual rainfall or soil fertility can cause an abrupt change in the social system as residents abandon unproductive soil to become environmentally-displaced persons (Reid et al., 2010). This systemic and synergic nature of global change renders it enormously complex to address, owing to the accumulation of feedback loops resulting from the process itself, often giving rise to new interconnected socioeconomic problems that, in turn, possess their own emerging properties (Steffen et al., 2005; Barnosky et al., 2012).
In addition, many of the alterations being inflicted by humans on the biosphere present characteristics rendering them especially problematic: they operate on nonlinear patterns and are difficult to forecast, which may lead to irreversible consequences for human time scales (Steffen et al., 2005; Reid et al., 2010). This unforeseeable and nonlinear nature of global change entails a considerable risk of eventually resulting in ecological collapse on a planetary scale (Scheffer et al., 2012; Bradshaw et al., 2021; Kemp et al., 2022; Willcock et al., 2023). It is therefore deemed necessary, if global change is to be kept within tolerable limits and at low risk of reaching critical thresholds of change, to identify and track the conditions on the Earth System with regard to its biogeophysical limits (Rockström et al., 2009), preventing their transgression by human actions and enhancing, as far as possible, the resilience of the global social ecological system (Reid et al., 2010; Scheffer et al., 2012).
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