Mario J. Molina, in a keynote speech opening the annual meeting of the American Chemical Society in Philadelphia, said new scientific analysis strengthens the link between human activity and climate change.
"People may not be aware that important changes have occurred in the scientific understanding of the extreme weather events that are in the headlines," said Molina, who shared a Nobel Prize in Chemistry in 1995 for his work on ozone depletion in the atmosphere.
"They are now more clearly connected to human activities, such as the release of carbon dioxide -- the main greenhouse gas -- from burning coal and other fossil fuels."
While here is no "absolute certainty" that global warming is causing extreme weather events, he said, scientific insights in the last year or so strengthen the link.
Even without certainty, he said, heat, drought, severe storms and other weather extremes may make the public more aware of global warming and the need for action.
"It's important that people are doing more than just hearing about global warming," Molina said. "People may be feeling it, experiencing the impact on food prices, getting a glimpse of what everyday life may be like in the future, unless we as a society take action."
2014: The Year in Music [PHOTOS]