In a world of worsening heatwaves, flooding, drought, glacial melting, megafires and other calamities of a changing climate, Gary Gragg is an optimist. As California warms, Gragg — a nurseryman, micro-scale farmer and tropical fruit enthusiast — looks forward to the day that he can grow and sell mangoes in Northern California. “I’ve been banking on this since I was 10 years old and first heard about global warming,” said Gragg, 54, who has planted several mango trees, among other subtropical trees, in his orchard about 25 miles west of Sacramento. Gragg’s little orchard might be the continent’s northernmost grove of mangoes, which normally are grown in places like Florida, Hawaii and Puerto Rico. Northern California’s climate, he said, is becoming increasingly suitable for heat-loving, frost-sensitive mango trees, as well as avocados, cherimoyas and tropical palms, a specialty of his plant nursery Golden Gate Palms. “Climate change isn’t all bad,” Gragg said. “People almost never talk about the positives of global warming, but there will be winners and losers everywhere.” Mangoes may never become a mainstream crop in the northern half of California, but change