China's promises to cut capacity have been a mirage and demand for key commodities in China has faltered, according to new third quarter China Beige Book data.

Why it matters: A commodities reversal would reignite skepticism over the Chinese economy with implications that go far beyond China, says CBB's president Leland Miller. A sustained fall of commodity prices due to China would impact confidence in the global economic recovery and could affect central bank interest rate policies.Go deeper: CBB pulls data from thousands of Chinese firms, including hundreds across the commodities sector. Bloomberg reports that data from CBB shows China's economy may be a "darker story" in 2018.