Qiang Wang suggests that shale gas might be used as a bridging fuel to cap China's carbon emissions (Nature 512, 115; 2014). Extraction and development problems could make this difficult.

The greenhouse-gas footprint of shale gas is much bigger than that of coal. Shale gas emits less carbon dioxide than coal or oil when burnt, but the methane produced during the extraction process has a global-warming potential 70 times that of CO2 (see R. W. Howarth et al. Nature 477, 271–275; 2011).

Following the US shale-gas boom, China devised a plan to extract its own gas resources. This proved difficult and expensive owing to limited water availability and because the gas is located at depth under large amounts of subsurface clay.

Furthermore, extraction might compromise the country's already stressed aquatic environments (H. Yang et al. Nature 499, 154; 2013) and increase seismic activity — important factors in densely populated areas such as southwest China.

As a result, Chinese shale-gas production in 2013 was only around 3% of that planned for 2015. Last month, this forced the country to halve its production target for 2020 (see go.nature.com/h5mtza; in Chinese).

In our view, China would be better off investing more in renewable energy and improving energy efficiency.