Once upon a time, Earth was colder, locked in its latest ice age. Eventually, roughly 14,000 years ago, things started thawing and the planet warmed back up. But that climate change, according to a new paper in Science, caused a major shift in vegetation. And if we don’t curb our fossil fuel use and cut carbon emissions soon, the authors say, we’ll see another big shift in plant life within 100 to 150 years.