In a surprising twist, a new UC Davis study shows winegrape quality has actually improved as temperatures have warmed over the last 60 years. The researchers worry, however, that the trend may have peaked and continued global warming could significantly disrupt the local economies of Napa and Bordeaux.

“Quality has increased steadily up to now,” said lead author Kaan Kurtural, a viticulture professor, in a news release. “We just don’t know the tipping point.”

The temperature threshold for optimal quality has remained elusive—winegrape growing has continued to exceed expectations under drastically changing climates. Rather than focusing on temperature, the researchers performed new analyses on sugar and color content, which raised alarms that the tipping point may be approaching.