That point moved north during both Northern and Southern Hemisphere summers, rather than moving farther south during the southern summer as the researchers expected. The shift was faster during Southern Hemisphere summers. The analysis also found an accelerating movement eastward, a pattern the authors said had not previously been reported.
A global signal built from regional changes
The green wave describes the seasonal progression of plant growth visible from space. To track it, the researchers combined satellite measures of vegetation greenness and leaf area with Earth system models, then calculated a weighted global center for each point in the seasonal cycle.
The centroid is a summary metric, not a claim that one continuous belt of plants is physically migrating. Greening in one region, browning in another and changes in growing seasons can all move the point. The paper says the result captures the combined effects of climate variability, ecosystem change, land use and land-cover change.
The team had expected the trajectory to stretch farther north in the Northern Hemisphere’s summer and somewhat farther south in the Southern Hemisphere’s summer. Instead, both seasonal positions shifted north. That reduced the north-south span of the trajectory, a contraction that the models project will continue this century. The authors say the metric could help researchers compare satellite observations with climate models and monitor changes in the terrestrial biosphere.
What the study does not show
Posts circulating the finding attribute global greening primarily to rising carbon dioxide and connect the PNAS result to several other statistics. Those numbers come from separate studies and need their original context.
A 2016 NASA summary reported that satellite records showed significant greening across roughly a quarter to half of vegetated land. Model simulations in that study attributed 70% of the observed greening to carbon dioxide fertilization. That was a model-based attribution from an earlier data set, not a measurement by the 2026 PNAS study. NASA also noted that CO₂ is the main driver of climate change and that plant-growth benefits can be constrained by water, nutrients and temperature.
Another widely shared figure says added leaf cover cools 93% of vegetated areas. In the NASA account of the underlying research, 93% refers to locations where a model produced lower land-surface temperatures when leaf area was increased. It does not mean 93% of vegetated land actually cooled. Looking at changes since 2000, the researchers found cooling in 30% of areas that gained leaf cover and warming in 5%. NASA described the net cooling as small compared with the pace and intensity of global warming, and the study measured land-surface temperature rather than near-surface air temperature.
NASA’s PACE satellite is useful for a different reason. Its first year of terrestrial observations ran from March 2024 to March 2025, not March 2025 to March 2026. The mission can distinguish plant pigments including chlorophyll, anthocyanins and carotenoids, offering a more detailed view of plant health. NASA’s PACE article does not attribute global greening to CO₂ or establish the green-wave shift reported in PNAS.
The new centroid offers a compact view of large-scale vegetation change, but it is not a single-cause meter. Determining how much of its movement comes from warming, carbon dioxide, land management, drought, fire or other regional changes requires additional attribution work.
