MILAN - US Secretary of State John Kerry warned Saturday that climate change was a threat to global security and has inflamed volatile situations from Europe's migration crisis to the Syrian conflict.

"Climate change is perhaps the most significant threat to global food security today. Make no mistake: the implications here extend well beyond hunger," he said just weeks before a key world climate conference in Paris.

"This isn't only about food security; it's about global security, period," he said during a speech at Milan's 2015 Expo.

Kerry said it was "not a coincidence that, immediately prior to the civil war in Syria, the country experienced the worst drought on record", sparking the migration of some 1.5 million people "that intensified the political unrest that was beginning to brew".

"I'm not suggesting the crisis in Syria was caused by climate change, obviously, it wasn't. It was caused by a brutal dictator who barrel bombed, starved, tortured, and gassed his own people.

"But the devastating drought clearly made a bad situation a whole lot worse," he said.

He described climate change as "threat multiplier".

"Even if it doesn't ignite conflict, it has the ability to fan the flames and to make situations much more complicated for political leaders to deal with."

Kerry cited the mass migration to Europe as an example of a crisis provoked partly by climate change -- which he warned will get significantly worse if large parts of the world become uninhabitable due to global warming.(AFP)