There's one issue that will define the contours of this century more dramatically than any other, and that is the urgent and growing threat of a changing climate.
We do not know how much our climate could or will change in the future. We do not know how fast change will occur or even how some of our actions could impact it.
Those who deny human-caused climate change offer no compelling evidence to better explain the undeniable rise in atmospheric concentrations of greenhouse gases and global temperature.
We need to start by having a conversation about climate change. It would be irresponsible to avoid the issue just because it's uncomfortable to talk about.
We are willing to uphold principles that have resulted in unprecedented prosperity and security throughout Europe and around the world. With the threat of climate change only becoming more urgent, Angela [Merkel] and I focused on the need for American and E.U. leadership to advance global cooperation.