Human activity began to transform the number and variety of plant species on Earth thousands of years ago, long before the Industrial Revolution, and might have had an even greater impact on vegetation than did the last ice age.

Ice entombed much of the planet from roughly 115,000 to some 20,000 years ago. Then, massive glaciers around the world started to retreat and global temperatures rose, resulting in dramatic alterations to Earth’s ecosystems.

To investigate how the abundance and composition of global vegetation changed after that thaw, Ondřej Mottl and Suzette Flantua at the University of Bergen in Norway and their colleagues analysed 1,181 fossilized pollen samples from the past 18,000 years. The pollen came from all continents except Antarctica.

The researchers found that global vegetation has been transformed, first by the climate changes that accompanied the end of the last glacial period. However, starting about 4,000 years ago, when agriculture intensified, the pace of change in global vegetation accelerated, reaching or exceeding the rate of change at the end of the most recent ice age.