China’s energy policies should balance air, carbon and water

China is in the process of shifting from using coal to natural gas, and is currently considering a range of natural sources.

Researchers from Princeton University have investigated the environmental impacts of transitioning from coal to natural gas in China. The team explored implications on air quality, water stress and carbon mitigation by the year 2020.

The researchers warn that the use of coal-based synthetic gas, known as SNG, would actually increase carbon emissions and water demand – especially in regions of China that currently have high carbon emissions and water scarcity per capita.

Overall, the researchers found that changing to natural gas meant air, carbon and water co-benefits, when methane leakage is controlled effectively.

“Assessing air quality, carbon emissions, and water scarcity impacts across local, regional, and global levels is crucial to capturing potential co-benefits while avoiding unintended consequences,” said first author of the study Dr Yue Qin, now a postdoctoral scholar at the University of California, Irvine.

“Although there is a lot of discussion on the need for a clean energy supply transition, in what sector the clean energy is used and what it is displacing is also critical in determining air quality, carbon, and water co-benefits,” said the principle investigator of the study, Professor Denise Mauzerall, at Princeton University‘s Woodrow Wilson School of Public and International Affairs and the School of Applied Science and Engineering.

“While the paper focuses on China, its general conclusions are widely applicable.”

China accounts for more than half of the world’s coal consumption, whereas natural gas, the world’s cleanest fossil fuel, accounts for only 6 per cent of China’s primary energy consumption. The global average is currently around 16 per cent.

For each of the six majour gas sources the researchers examined the impacts of substituting coal with the natural gas. Gases were chosen based on government and industrial plans, and included conventional gas, synthetic natural gas, shale gas, imported liquefied natural gas, imported Eastern Russia gas, and imported Central Asia gas.

The researchers found that replacing coal with natural gas (except for coal-based synthetic gas) has benefits for air quality, carbon mitigation and water stress. It would lead to substantial CO₂ emission reductions, and reductions in water use.

“Our findings show why it is critical to understand the underlying air-carbon-water synergies and trade-offs so that China, as well as other developing countries, can properly design clean energy transition pathways according to their local environmental priorities,” Dr Qin said.

“The development of new energy systems provides an opportunity to simultaneously reduce multiple environmental impacts including domestic air pollution, local water scarcity, and global climate change,” Prof Mauzerall said. “Ultimately, a full transition away from carbon-based fuels will be necessary to address climate change. In other research we have found that renewable energy provides the largest co-benefits for air quality, carbon mitigation, and reduced water consumption of any known energy sources.”

The findings of the study were published in Nature Sustainability.