The United Nations has released a report that compresses humanity's timeline for confronting climate change, finding that critical warming thresholds will be crossed sooner than previous models anticipated. Researcher Kristie Ebi and her international colleagues are not delivering new science so much as sharper science — one that reflects the growing precision of climate observation and the accelerating response of Earth's systems to accumulated greenhouse gases. What shifts is not the physics of warming, but the clock by which we must live with its consequences. The world's window for adaptat