Emissions cuts using biofuels could worsen water stress in US, study suggests
Using biofuels as a way to cut greenhouse gas emissions could put US water resources under increasing pressure, a new study suggests. Researchers find that a heavy reliance on bioenergy could mean a 42% increase in water consumption across the US by 2100.
The results show that policies to mitigate climate change need to be carefully planned to avoid knock-on effects on natural resources, the researchers say.
The new study, published in Proceedings of the National Academy of Sciences, analysed "water deficits" across the US. Deficits occur when demand for water outstrips the supplies available in local or neighbouring rivers and reservoirs.
Using computer models, the researchers simulated how these deficits might change with different approaches for tackling global carbon emissions to limit the impacts of climate change.
The results show that measures to cut carbon emissions could mean water deficits are more severe by the end of the century.
The study compared the impact on water stress of two scenarios, or representative concentration pathways, for how we deal with rising carbon emissions. RCP4.5 describes a world where the concentration of carbon dioxide in the atmosphere is stabilised at around 650 parts per million (ppm) by 2100.
In contrast, RCP8.5 is a future where emissions are not curbed and carbon dioxide concentrations rise to around 1,370ppm by 2100. The paper refers to RCP8.5 as a "business-as-usual" scenario.
In RCP4.5, bioenergy forms an important alternative to fossil fuels, alongside renewables and nuclear. Biofuels are also combined with carbon capture and storage to produce electricity with negative emissions.
The researchers considered just one type of biofuel, which is switchgrass. This a perennial grass that grows across much of the North American prairies. It can be used to make ethanol or be burnt directly for heating or electricity generation.
But while these biofuels helps cut emissions, they need a lot of water to grow. The simulations show that water consumption across the US could increase 42% by 2100 under RCP4.5. Much of this increase could be for irrigating biofuel crops, the researchers say.
The results of the new study highlight that there are smart ways to reduce emissions and "stupid" ways, says Dr Peter Gleick, president and co-founder of the Pacific Institute, an organisation established to help find solutions to global water challenges. He tells Carbon Brief:
"The stupid ones are those that reduce emissions of greenhouse gases, but make other problems worse. In this case, attempting to mitigate greenhouse gas emissions by replacing fossil fuels with biofuels falls into [this] category - something people have argued for a long time - precisely because of the massive pressure biofuels place on water resources."