We, the human species, are confronting a planetary emergency—a threat to the survival of our civilization that is gathering ominous and destructive potential even as we gather here. But there is hopeful news as well: we have the ability to solve this crisis and avoid the worst—though not all—of its consequences, if we act boldly, decisively and quickly. However, too many of the world’s leaders are still best described in the words of Winston Churchill applied to those who ignored Adolf Hitler’s threat: "They go on in strange paradox, decided only to be undecided, resolved to be irresolute, all powerful to be impotent." So today, we dumped another 70 million tons of global-warming pollution into the thin shell of atmosphere surrounding our planet, as if it were an open sewer. And tomorrow, we will dump a slightly larger amount, with the cumulative concentrations now trapping more and more heat from the sun.