Yes, Earth’s climate has waffled around for as long as the planet has existed. But it has happened slowly over the course of millennia. Right now, our climate is changing faster than it ever has in 22,000 years, and we know why: we’re pumping carbon dioxide and other greenhouse gas into the atmosphere. We have known that these gases cause warming since the early 19th century. This is not a new science. But for some reason we’re still arguing about it.