This Is What Our Hellish World Will Look Like After We Hit the Global Warming Tipping Point The de facto assumption of climate change policy is that the world must limit the increase in global temperatures to 3.6 degrees Fahrenheit (2 degrees Celsius) above pre-Industrial levels, or risk hitting a tipping point where the impact becomes irreversible. The figure dates back to 1975, when economist William Nordhaus suggested that more than 3.6 degrees of warming would “take the climate outside of the range of observations which have been made over the last several hundred thousand years.” By the 1990s, 3.6...