The annual clock of the seasons – winter, spring, summer, autumn – is often taken as a given. But our new study in Nature, using a new approach for observing seasonal growth cycles from satellites, shows that this notion is far too simple.

We present an unprecedented and intimate portrait of the seasonal cycles of Earth’s land-based ecosystems. This reveals “hotspots” of seasonal asynchrony around the world – regions where the timing of seasonal cycles can be out of sync between nearby locations.

We then show these differences in timing can have surprising ecological, evolutionary, and even economic consequences.

The seasons set the rhythm of life. Living things, including humans, adjust the timing of their annual activities to exploit resources and conditions that fluctuate through the year.

The study of this timing, known as “phenology”, is an age-old form of human observation of nature. But today, we can also watch phenology from space.

With decades-long archives of satellite imagery, we can use computing to better understand seasonal cycles of plant growth. However, methods for doing this are often based on the assumption of simple seasonal cycles and distinct growing seasons.

This works well in much of Europe, North America and other high-latitude places with strong........

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