We know that climate change is already occurring, and that additional warming is unavoidable. If we hope to limit the negative impacts of climate change, we must prepare by identifying vulnerabilities and by planning accordingly. Climate change is one of the most challenging problems that humanity has ever faced. At stake are hundreds of millions of lives, innumerable species and ecosystems, the health and viability of the economy, and the future habitability of this planet. Fortunately, climate change is solvable. We have the technologies. We have the science. We now need the leadership—and the courage to change course.