President Barack Obama has joined 150 other leaders in Paris for a critical summit on global warming, and he’s sounding the alarm.

The 11-day event may be the most important in the history of the effort to combat climate change, and Obama spoke to the summit about the tough changes that would need to happen in order to humanity to weather the coming storm, according to a report from The Australian.

The United States is the second biggest contributor of carbon dioxide after China.

Obama warned at the event that “we are going to have to devote more and more of our economic and military resources, not to growing opportunity for our people, but to adapting to the various consequences of a changing planet,” he said according to the report, adding: “This is an economic and security imperative that we have to tackle now.”

The United Nations wants a deal to cut carbon emissions and provide billions of dollars in aid to countries that will suffer from the ill effects of global warming, with problems such as drought, extreme weather, flooding, and a host of other threats.

The Paris summit represents a promising step toward addressing climate change, but an agreement is threatened by arguments over who should bear most of the burden for dealing with the problem. Also, many countries deal with immediate economic concerns and feel that they don’t have the luxury of worrying about problems decades or even centuries down the road when their people need the benefits of burning fossil fuels today.

The Paris summit is a critical one: it represents a chance for leaders of most of the nations around the world to come to an agreement on how to tackle the problem, and missing an opportunity to do so would be a huge blow to the effort to fight global warming.