“Yet the very same people who said we'll all be dead in 12 years because of global warming, a name since reborn to climate change because the planet was cooling, not warming, and nobody was dead.”

The planet was not cooling. The World Meteorological Organization confirmed that 2015 through 2025 were the eleven warmest years on record in all eight global datasets, with 2025 about 1.44 degrees Celsius above the 1850 to 1900 average. Nor was the term changed for that reason: NASA uses both, and explains that global warming means the long-term heating of the Earth's surface while climate change covers the broader set of changes. The twelve-year figure came from an emissions deadline rather than a date of death: the 2018 special report on 1.5 degrees found that net global carbon dioxide emissions needed to fall about 45 percent from 2010 levels by 2030 and reach net zero by around 2050. On the last clause, the World Health Organization projects climate change to cause about 250,000 additional deaths a year between 2030 and 2050 from undernutrition, malaria, diarrhoea and heat stress alone.

Someone did say something close to it, and that is the claim's best defence. In January 2019 Representative Alexandria Ocasio-Cortez said the world is going to end in 12 years if climate change is not addressed, apparently drawing on the same report. That supports the attribution and nothing else in the sentence.