The aluminum industry’s best days might be in the rear view mirror.

At North America’s largest aluminum conference Wednesday, researcher Harbor Intelligence warned an audience of 870 producers, traders and buyers—many of them sipping Johnnie Walker Gold Label scotch—that the price of the lightweight metal will plummet almost 20% by December to $2,310 per ton as demand ebbs and supplies build in warehouses across the globe.

“We all know that last year and so far this year has been the best ever in terms of demand,” Harbor’s managing director Jorge Vazquez said at the conference. “But there’s one component of that demand borrowed from the future, and we’ll need to pay that—consumers cannot sustain this level of goods spending seen the past two years.”

Aluminum prices surged more than 40% last year as demand soared, producers continued to battle shortages and supply chain issues lingering from the global pandemic. This week struck a much more muted tone than 9 months ago when industry players met in person for the first time since the pandemic started, while the metal was riding the best rally in a decade.

To be sure, customer demand remains robust. The cost to ship aluminum remains at historically elevated levels, indicating ocean freight, trucking and other handling into the North American region remains higher than the rest of the globe.

Still, the worries about slowdowns, inflation and ongoing supply chain snags remain. Novelis Inc., a massive US producer of so-called flat-rolled products that already announced nearly $3 billion in new investments this year, said they’ll continue to have to deal with inflation and the supply chain crisis heading into next year. Norsk Hydro ASA, one of the world’s largest aluminum producers, said demand may be softening. The company said its biggest concern is the trend continuing into next year.

“On the margins, especially probably in Europe where there’s a little more uncertainty, you start to see some” softening demand, said Jesse Gary, the chief executive of US producer Century Aluminum Co. “You can start to see it in non-core markets a little bit here” in the US.

Aluminum for delivery in three months fell 2.2% to $2,756.50 a ton at 3:56 p.m. on the London Metal Exchange.