Negative effects of climate change such as extreme drought are linked to deadly violence in countries such as Syria and Nigeria, and those still denying there's a problem are putting the entire planet at risk, the US secretary of state said.
John Kerry addressed a group of about 2,000 people on Tuesday at the Old Dominion University in Norfolk, Virginia.
"It's not a coincidence that immediately prior to the civil war in Syria the country experienced its worst drought on record, as many as 1.5 million people migrated from Syria's farms to its cities, intensifying the political unrest that was just beginning to royal and boil in the region," said Kerry.
"In Nigeria, climate change didn't lead to the terrorist group Boko Haram, but the severe drought that the country suffered and the inability of the government to cope with it helped create the political and economic vitality that the militants exploited to seize villages, butcher teachers, and kidnap hundreds of school girls," he added.
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Kerry's comments came ahead of a meeting that will bring 195 countries together to seek a binding climate change agreement aimed at limiting the rise in global temperatures. The UN Framework Convention on Climate Change lasts from November 30 until December 11 in Paris, France.
Kerry had earlier said he was convening a task force to integrate climate and security analysis into broad foreign policy planning.
"It would be better for all of us if I was exaggerating the urgency of this threat, but the science tells us unequivocally that those who continue to make climate change a political fight put us all at risk."
Elsewhere, US President Barack Obama spoke by phone to India's Prime Minister Narendra Modi on Tuesday about climate change.
Saudi Arabia, whose oil-fuelled economy could suffer from global efforts to reduce greenhouse gas emissions, also submitted a climate-action pledge to the UN.
Though thin on commitments, the Saudi pledge was symbolic because the desert kingdom has been seen as reluctant to join the fight against global warming.
The pledge mainly focused on efforts to diversify the Saudi economy and study the impact on it by international policies aimed at tackling climate change.
The kingdom said it was aiming "to achieve mitigation co-benefits ambitions of up to 130 million tonnes of carbon dioxide equivalent avoided by 2030 annually through contributions to economic diversification and adaptation".