The impacts of climate change on terrestrial Earth surface systems
Jasper Knight1* and Stephan Harrison2
1School of Geography, Archaeology and Environmental Studies, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa.
2College of Life and Environmental Sciences, University of Exeter, Penryn, TR10 9EZ, UK. *e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
National and international policy initiatives have focused on reducing carbon emissions as a means by which to limit future climate warming. Much less attention has been paid by policymakers to monitoring, modelling and managing the impacts of climate change on the dynamics of Earth surface systems, including glaciers, rivers, mountains and coasts. This is a critical omission, however, as Earth surface systems provide water and soil resources, sustain ecosystem services and strongly influence biogeochemical climate feedbacks in ways that are as yet uncertain. We argue that there is a significant policy gap regarding the management of Earth surface systems’ impacts under climate change that needs to be closed to facilitate the sustainability of cross-national Earth surface resource use. It is also a significant challenge to the scientific community to better understand Earth surface systems’ sensitivity to climate forcing.
The Intergovernmental Panel on Climate Change (IPCC) showed in its fourth assessment report that different biophysical environments are likely to exhibit different responses to ongoing climate change1. Generic properties of these environmental responses include spatial and temporal variability, nonlinearity, feedbacks involving different biogeochemical processes and time lags. The context for understanding these environmental responses is brought into focus by many recent studies showing that, irrespective of future greenhouse-gas emissions, a mean surface temperature increase of 2 °C (over 1990 levels) is inevitable, and an increase of 4 °C or more is not unlikely by 2100 (refs 2,3). Biosphere responses to global climate change are relatively well understood. Studies show that climate change alters biospheric systems’ internal dynamics and interconnectedness, for example, between plant phenology and insect behaviour4,5. Biome and species’ range shifts, both laterally and by elevation, are now taking place in response to climate forcing6,7. The importance of such range shifts for ecosystem structure and function, biodiversity, endemism and gene flow has been widely recognized7, and there is much policy debate on management of biosphere responses to climate change8,9.
By contrast, Earth surface (or geomorphological) system responses to climate change are poorly understood. Earth surface systems in terrestrial environments tend to work over longer timescales and be more strongly affected by antecedent conditions and nonlinearity than their biological counterparts10,11. Observations of key variables that denote the response of Earth surface systems to climate forcing — such as river discharge, permafrost temperature and slope mass movements — are generally of short (decadal) duration and measured from specific field sites often using different methodologies12. These observations are also difficult to scale up, temporally or spatially, in such a way that they are compatible with analysis of satellite imagery and output from geophysical models and global climate models (GCMs). For these reasons, and the false perception that Earth surface systems are not significantly vulnerable to climate change, international discussion and policy has not focused on understanding and managing climate impacts on these systems.
Here we outline the reasons why Earth surface system processes and their feedbacks to the climate system and biosphere on different scales are a critical element of global responses to ongoing climate forcing, suggest the best tools to identify and predict changes in Earth surface systems, and show why the challenges posed by these processes and feedbacks require a considered and concerted scientific and climate policy response.
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