It was around noon on Sunday and the crowds had gathered in Adelaide for the first day of Australia’s Tour Down Under.

As the cyclists whizzed past, a group of elderly women turned their backs and pulled down their skirts. Beneath their naked bottoms, six big letters spelled out Santos — the oil and gas company sponsoring the first major race on the professional cycling calendar — to chants of "we got rid of Big Tobacco, we’ll get rid of Santos too.”

Santos did not respond to a request for comment. But the Australian protest sets the stage for a year of radical action by climate activists who are pushing to end advertisements and sponsorships they say allow fossil fuel companies to burnish their reputations while profiting from products that heat up the planet. The campaign is beginning to gain traction as a year of extreme weather, from floods to droughts, keeps climate change in the headlines.