SYDNEY, Australia — One climate activist halted train service by chaining himself to the tracks. Others have glued themselves to busy roads, causing gridlock. And just last week, protesters locked arms to stop people from entering a mining conference before being forcibly dispersed by police officers with pepper spray.

A surge of climate activism is flooding Australia as the country falls behind on its promise to reduce emissions — effectively ignoring the Paris Agreement the Trump administration just abandoned. Prime Minister Scott Morrison has responded with a threat that’s alarmed scientists and free speech advocates, arguing that the government should outlaw “indulgent and selfish” efforts by environmental groups to rattle businesses with rallies and boycotts.

“The right to protest does not mean there is an unlimited license to disrupt people’s lives,” Mr. Morrison said, adding, “I am very concerned about this new form of progressivism.”

Australia’s “climate wars,” once confined to election campaigns, are now spilling into the streets with some of the biggest protests the country has ever seen. An increasingly outraged public is demanding action while the conservative national government refuses to budge, relying on the police to squelch dissent.