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.
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 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.