Sources, intensities, and implications of subsurface warming in times of climate change

Abstract

Anthropogenic warming of the atmosphere is one if not the most pressing challenge we face in the 21st century. While our state of knowledge on human drivers of atmospheric warming is advancing rapidly, little so can be said if we turn our view toward the Earth’s interior. Intensifying land use and atmospheric climate change condition the changing thermal state of the subsurface at different scales and intensities. Temperature is proven to be a driving factor for the quality of our largest freshwater resource: groundwater. But there is only insufficient knowledge on which sources of heat exist underground, how they relate in their intensity of subsurface warming, and which consequences this warming implies on associated environments, ecosystems and resources. In this review, we propose a differentiated classification based on (1) the geometry of the heat source, (2) the scale at which the subsurface is heated, (3) the process that generates the heat, and (4) the intention of heat release. Furthermore, we discuss the intensities of subsurface warming, the density of induced heat fluxes, as well as their abundance, and draw implications for depending processes and ecosystems in the subsurface and the potential of recycling this waste heat with geothermal installations.

Graphical abstract

Keywords:

• Climate change
• geothermics
• groundwater quality
• subsurface temperature
• thermal environment
• waste heat

HANDLING EDITORS:

• Binoy Sarkar and Yong Sik Ok

Acknowledgments

We thank Ryan Pearson for language editing. We would also like to thank Cathrin Dreher (Umweltamt Berlin), Rudolf Hunold and Stefan Schiffmann (RheinEnergie AG) as well as Harald Zauter (LAF Sachsen-Anhalt) for their valuable support with data and additional information.

Disclosure statement

The authors declare no competing interests.

Author contributions

M. Noethen and P. Bayer wrote the first draft of the manuscript, H. Hemmerle contributed to figure creation and layout. H. Hemmerle and P. Bayer reviewed and edited the manuscript before submission.

Additional information

Funding

This work was supported by a scholarship from the German Federal Environmental Foundation (DBU) to M. Noethen.