Global greening: The Earth’s green wave is shifting

(Press-News.org) A team of scientists led by the German Centre for Integrative Biodiversity Research (iDiv), the Helmholtz Centre for Environmental Research (UFZ), and Leipzig University has developed a new method to track the Earth’s greenness – a key indicator of vegetation health and activity – by calculating its centre of mass.

Lead author Prof. Miguel Mahecha explains: “Imagine holding a perfectly round globe in your hands and attaching small weights to it, each representing the green leaves at every point on the Earth’s surface. If you then carefully place this globe into calm water, the centre of mass will always point downward.” Mahecha is a researcher at Leipzig University, the Helmholtz Centre for Environmental Research (UFZ), and a member of iDiv.

Earth’s green centre shifts continuously
Using satellite observations and model data, the researchers tracked how this “green centre” shifts over time. In rhythm with the seasons, vegetation greenness moves like a green wave from north to south and back each year. By tracking the centre of this wave – its direction and velocity – the team found it oscillating between its northernmost position in mid-July in the North Atlantic near Iceland and its southernmost position off the coast of Liberia in March.

The study, published in the journal PNAS, sheds new light on global greening and its acceleration – a less widely known aspect of global change referring to the overall increase in vegetation density worldwide. Like climate and biodiversity change, global greening is largely driven by human activities. Rising atmospheric CO₂ acts as a fertiliser, enhancing photosynthesis, while higher temperatures extend growing seasons in many regions.

When analysing changes in the green wave over several decades, the researchers detected a consistent northward shift across all seasons. Contrary to their expectations, they did not observe a southward shift during the Southern Hemisphere summer.

Unexpected shift to the north
“This was a huge surprise to us,” says Mahecha. “Longer growing seasons and warmer winters in the Northern Hemisphere, which allow vegetation to remain slightly greener for longer, may be driving the Earth’s overall greening shift throughout the year. However, this is a hypothesis that we need to explore further.”

In addition to the northward movement, the team also identified a distinct eastward shift. According to the researchers, this pattern is likely linked to pronounced greening hotspots in eastern regions such as India, China, and Russia.

Tracking the Earth’s seasonal greening and effectively measuring how fast and in which direction it is changing connects multiple facets of global change, including climate–biosphere interactions, land-use change, fire dynamics, droughts, and animal migration. The new method therefore provides a powerful tool for understanding how the living surface of our planet is reorganising in a warming world.

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