# Accelerated north–east shift of the global green wave trajectory

## TL;DR

The global green wave, representing seasonal vegetation shifts, is moving northeastward faster, indicating changes in Earth's biosphere due to climate and land use.

## Contribution

A novel method to track the centroid of the global green wave, revealing directional shifts and acceleration in its movement.

## Key findings

- The green wave centroid shifts northward during both boreal and austral summers, with a stronger shift in austral summer.
- An accelerating eastward movement of the green wave trajectory has been detected.
- The amplitude of the green wave trajectory is decreasing, expected to intensify in the future.

## Abstract

Earth’s vegetation follows a rhythmic “green wave” that moves seasonally across the globe. It shapes the life cycles of organisms, biogeochemical cycles, and climate feedbacks, but until now, no intuitive metric existed to track its dynamics. We present a method to track the wave’s center of mass. This “flight path” of the green wave’s centroid reveals a measurable directional drift of ecosystem functioning: The green wave is shifting, with faster changes during Southern Hemisphere summers and an overall northeastward movement. This approach expresses planetary change caused by land use and climate change in kilometers over decades and offers a basis to monitor biosphere dynamics and their interaction with Earth system dynamics and human activity.

Viewed from space, a “green wave” seasonally traverses Earth’s surface, from the north in boreal summer to the south in austral summer. This wave represents vegetation phenology, driven primarily by solar irradiation and modulated by climate variability and ecosystem dynamics. Despite its significance for multiple Earth system processes, we lack a unified metric to characterize and understand its dynamics. Here, we propose a concept to quantify global phenology by tracking the green wave’s centroid using satellite and Earth system model data. The resulting trajectory summarizes global phenological dynamics and directional trends. Earlier reports on global greening led us to hypothesize a rapidly northward shifting trajectory during boreal summer and a moderate southward shift during austral summer. Contrary to this expectation, we find that the centroid moves northward during both summer periods, with the austral summer shift consistently exceeding the boreal shift across datasets. As a consequence, the amplitude of the green wave trajectory is decreasing, a trend projected to intensify throughout this century. We also detect an accelerating eastward shift, a phenomenon not previously reported. Tracking the green wave’s centroid reveals how regionally changing land dynamics affect the global functioning of Earth’s terrestrial biosphere.