Scientists Observed Earth's Seasons From Outer Space And Made A Fascinating Discovery

An August 2025 study published in Nature reveals that the seasons aren't quite as synchronous as previously believed. The paper's lead author, Drew Terasaki Hart from the University of California, Berkeley, says (via The Conversation) that the findings demonstrate how the notion of "the annual clock of the seasons ... is far too simple." Instead, the seasonal cycles in two nearby regions of the world can be completely out of sync with one another by as much as a couple of months.

This new, intimate understanding of seasons stems from the branch of science known as phenology, which is the study of the interaction between the climate and biological systems. Oftentimes in phenology, scientists explore more micro-scale interactions, such as the migration of hummingbirds in places like South Florida or the blooming of flowers in Antarctica. However, Hart earned his PhD in environmental science by looking broader. His work utilizes satellite imagery to study evolutionary biogeography on a global scale, examining the rhythms of Earth's ecosystems as they respond to seasonal climatic fluctuations.

The study analyzed 20 years of satellite imaging to compile and compare terrestrial plant growth cycles, and it painted a picture of seasonal complexity far beyond our previous understanding. For example, Phoenix, Arizona, and Tucson, Arizona, are only about 100 miles apart, and they're both approximately along the same latitude. Surprisingly, the study demonstrates that the two nearby cities have dramatically different cycles of plant growth, meaning that their seasonal cycles are also, essentially, out of sync. The most extreme regions of seasonal asynchronicity, however, are mountainous tropical regions, where two valleys separated by a day's drive can experience seasonal plant blooms in different months. In other words, the traditional concepts of winter, spring, summer, and autumn need not apply.

Phenology from a global perspective has existed for ages, but the technology for analyzing satellite data is truly cutting edge. Drew Terasaki Hart's team used novel analysis tools and a complex methodology to generate an uninhibited view of plant blooms around the world. In short, the study's maps have an unprecedented degree of detail — the kind of quality improvement you'd expect from increasing the resolution of a video (or a satellite photograph).

With the newly enhanced resolution, the resulting map of land surface phenology, or seasonal changes of plant blooms across the globe, is quite beautiful. One of the videos, credited to Hart and CSIRO, was shared on YouTube under the title "Timing of global average phenocycles." To the untrained eye, the video showcases the parts of the Earth that are green at different times of the year, indicating plant life. But to Hart and his team, the high resolution helped lead to the discovery of phenological diversities that had previously been hidden from view. 

The team used Google Earth Engine to compile over 20 years of satellite images. (In fact, Google Earth is one of the best sources for satellite images of the globe, and it's free for researchers and non-commercial users.) From there, as they explained in their Nature study, the data was processed in Python by applying a dozen "core scientific packages," which are essentially software filters that help highlight plant growth. The result is something akin to a heatmap of plant blooms. 

Every culture has its own unique definitions of seasons, which are based on factors like rainfall, sunlight, and temperature. Ultimately, such definitions are tied to the ways in which we depend on the environment, such as agricultural harvests, water access, and the habitability of an ecosystem. In a sense, the study of phenology is a study of our own evolution. 

Thus, the insights provided by Drew Terasaki Hart and his team have implications for human beings as well, especially as human activity changes the environment. For one, it serves as a reminder of how delicate and self-contained ecosystems can be. Some of the most biodiverse regions in the world are also some of the most consistent seasonally — you can see that in the weather and climate of rainforests. Yet, Hart's team's study demonstrates that two Colombian coffee farms just a few hours away from each other can have dramatically different seasons. This observation suggests that even small changes in local climate and geography, such as those resulting from climate change and human activity, can have significant consequences for how well an ecosystem will adapt.

More emerging phenology research points in the same direction: Life adapts to sudden environmental changes in intricate, complex ways. For instance, one 2020 paper from the University of Washington (published in the journal Trends in Ecology & Evolution) demonstrated that when animals move in search of resources, they depend on the "spatiotemporal configuration" of their environment. In other words, animals can adapt to food deficits by moving to new environments; however, their success is largely determined by the geographical layout of those resources. If humans impede their movement with the construction of a dam or highway, for example, even the most resilient species will struggle to survive. It seems ecosystems are more delicate than they might appear.