Global shifts in Earth’s seasonal green wave

In response to solar forcing, hydrometeorological variability, and ecosystem properties, a global seasonal oscillation of vegetation greenness can be observed from space. This “green wave” plays a central role in regulating carbon uptake, energy exchange, and biosphere–atmosphere interactions. Yet, the dynamics of this large-scale macrophenological signal have so far been described mainly through summary statistics of local or pixel-based indicators. A concise global descriptor of the green wave is still lacking. Here, we introduce a metric that characterizes global vegetation seasonality by computing the spatio-temporal center of mass of terrestrial greenness from satellite observations. 

The resulting global three-dimensional trajectory provides an intuitive and integrative representation of seasonal and interannual macrophenological variability. Based on earlier evidence of widespread greening in the northern hemisphere, we expected a strong poleward displacement during boreal summer and a weaker compensating shift during austral summer. Instead, we find a consistent northward displacement during both seasonal phases. Across independent datasets, the austral summer shift exceeds the boreal one. This asymmetry leads to a contraction of the annual latitudinal amplitude of the green wave, a tendency that further strengthens in future projections using CMIP6 models. The proposed trajectory framework offers a new way to quantify and communicate large-scale biosphere change in physically interpretable units, and provides a basis for linking vegetation dynamics to climate forcing and human land use.