As the world's largest unfrozen freshwater resource, groundwater is crucial for life on Earth. Researchers have investigated how global warming is affecting groundwater temperatures and what that means for humanity and the environment. Their study indicates that by 2100, more than 75 million people are likely to be living in regions where the groundwater temperature exceeds the highest threshold set for drinking water by any country.
Earth's climate system is heating up due to the atmosphere's increased concentration of greenhouse gases, which limits the amount of heat that can be radiated away. The oceans absorb a substantial fraction of this heat, but soil and groundwater also act as heat sinks. However, little is known thus far about the effects Earth's surface warming has on groundwater over space and time.
A further effect of increased near-surface and groundwater temperatures is that critical thresholds can be exceeded in water distribution networks. This could have human health implications, e.g. by promoting the growth of pathogens such as. Fish species, especially salmon, are also affected by the changing conditions. Their reproduction could be endangered if groundwater-dependent spawning grounds in rivers become too warm.