"Science has a good understanding of past climate changes and their causes, and that evidence makes the human cause of modern climate change all the more clear. Greenhouse gasses – mainly CO2, but also methane – have been implicated in most of the climate changes in Earth’s past. When they were reduced, the global climate became colder. When they were increased, the global climate became warmer. When changes were big and rapid (as they are today), the consequences for life on Earth were often dire – in some cases causing mass extinctions."