The year is 2100, and the world’s 12 billion people are still burning fossil fuels with abandon. Compared with preindustrial times, the planet has warmed by 4.5 degrees Celsius, or 8.1 degrees Fahrenheit. The atmosphere is filled with greenhouse gases, and parts of the Earth sometimes experience temperatures too extreme for humans. This bleak vision of the future has long played a significant role in scientific assessments of global warming. Sometimes called the “business as usual” scenario, it represents a worst case where countries continue to burn oil, gas and coal unabated — in contrast with a world where emissions have been dramatically reduced, and global warming is more moderate. But now, some climate scientists and energy experts say the worst-case scenario is increasingly unlikely. That’s stirred debate within the research community over whether a rare bit of good news about global warming has emerged or if, instead, the […]