According to satellite observations, global mean vegetation greenness reached a new record high in 2025.

A “Year in Review” analysis published in Nature Reviews Earth & Environment (April 2026) reports that 2025 set a record for global vegetation greenness (measured primarily via growing-season NDVI from MODIS and related products).

Key details from the analysis:

• 68.2% of vegetated land surfaces showed greening (up from 67.7% in the prior record year of 2024).
• Herbaceous ecosystems dominated the signal: 72.1% of grasslands and 77.6% of croplands greened.
• Hotspots included southern Africa, southern South America, northern Australia, Europe, central North America, and northern China — often aligned with increased precipitation.
• About 60% of forests greened (somewhat lower than in 2024).
• Browning occurred in places such as eastern Siberia (linked to anomalously cold growing-season temperatures). Tropical rainforest signals showed some uncertainty between sensors (MODIS vs. VIIRS) related to recovery after the 2023–2024 El Niño.

This continues a well-documented long-term “global greening” trend observed since the 1980s in satellite records (NDVI, LAI, and related indices).

Earlier studies attributed a large share (often ~70% in some analyses) of the multi-decadal increase to the CO₂ fertilization effect, with additional contributions from climate factors (warming, precipitation changes), nitrogen deposition, and land management (e.g., agriculture intensification and reforestation, notably in China and India).

Note that greening is not uniform: regional browning, drought/heat impacts, and differences between ecosystem types persist, and some years show strong interannual variability. The 2024 and 2025 records followed a previous peak around 2020.

Overall leaf area and photosynthetic activity have increased substantially over decades (estimates of >15% in some long-term metrics), with implications for carbon uptake, agriculture, and the water cycle, though these do not eliminate other climate-related concerns.

In short, the satellite record confirms another record year of global vegetation greenness in 2025 as part of an ongoing multi-decadal trend.

The CO2 fertilization effect refers to the stimulation of plant growth and photosynthesis by elevated atmospheric CO2 concentrations. It is a primary driver of observed global greening and contributes to the terrestrial carbon sink. The core mechanisms operate at the biochemical, physiological, and whole-plant levels, with the strongest responses typically in C3 plants (most trees, crops like wheat/rice/soybean, and many temperate/tropical species). C4 plants (e.g., maize, sugarcane) show weaker direct responses due to their inherent CO2-concentrating mechanisms.

Photosynthesis in C3 plants is often limited by CO2 availability at current atmospheric levels (~420 ppm). The key enzyme is Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase), which catalyzes the fixation of CO2 onto ribulose-1,5-bisphosphate (RuBP) in the Calvin-Benson cycle.

Increased substrate availability: Higher atmospheric CO2 raises intercellular (Ci) and chloroplastic CO2 concentrations. This increases the rate of the carboxylation reaction (CO2 addition), boosting net carbon assimilation (Anet or photosynthesis rate). At low Ci, photosynthesis rises steeply with CO2; the response saturates at higher levels when limited by RuBP regeneration (electron transport) or triose-phosphate utilization.

Suppression of photorespiration: Rubisco can also oxygenate RuBP when O2 competes with CO2, leading to photorespiration—a process that releases previously fixed CO2 and consumes energy (ATP/NADPH) without net carbon gain. Elevated CO2 increases the CO2: O2 ratio at the enzyme’s active site, competitively inhibiting oxygenation. This reduces carbon and energy losses, further increasing net photosynthesis.

These effects are described by the Farquhar-von Caemmerer-Berry (FvCB) model of photosynthesis. Short-term responses can increase light-saturated photosynthesis by ~20–50% (or more under certain conditions) for a doubling of CO2, though long-term gains are often moderated.

Elevated CO2 triggers partial stomatal closure (reduced stomatal conductance, gs) in both C3 and C4 plants.

Sensing and signaling: CO2 (or bicarbonate) is sensed in guard cells via carbonic anhydrases and protein kinases (e.g., HT1, MPK4/12 pathways), leading to ion fluxes that reduce guard cell turgor and close stomata. This can occur independently of (or in interaction with) photosynthetic sugar signaling.

Consequences: Lower gs reduces water vapor loss (transpiration) while still allowing sufficient CO2 uptake due to the steeper CO2 diffusion gradient. This raises intrinsic water-use efficiency (iWUE = Anet / gs), often roughly in proportion to the CO2 increase under optimality theory. Plants can maintain or increase carbon gain with less water use, which is particularly beneficial in drier conditions and can increase soil moisture.

Meta-analyses of free-air CO2 enrichment (FACE) experiments typically show ~20–30% reductions in gs.

Downstream and Indirect Effects

Increased carbohydrate production and growth: Higher photosynthesis produces more sugars (e.g., sucrose, starch), which can support greater biomass accumulation, leaf area expansion, root growth, and reproductive output—provided sinks (growing tissues) can utilize the extra carbon.

Resource-use efficiencies: Improved nitrogen- and light-use efficiency often occurs as plants optimize investment (e.g., reallocating nitrogen away from excess Rubisco).

Acclimation (downregulation): Prolonged elevated CO2 frequently leads to partial downregulation of photosynthetic capacity (lower Vcmax, reduced Rubisco content/activity, and sometimes lower Jmax). This is often linked to sink limitation (carbohydrate buildup feedback-inhibits photosynthesis), nutrient constraints (especially nitrogen), or developmental adjustments. Despite acclimation, net photosynthesis at the elevated growth CO2 is usually still higher than at ambient levels.

Whole-plant and ecosystem scaling: Extra carbon can increase leaf area index (contributing to “greening”), alter allocation (roots vs. shoots), and interact with other factors (temperature, water, nutrients, light). These scale up to higher gross primary production (GPP) and, under favorable conditions, greater net primary production and carbon sequestration.

The fertilization effect is not unlimited or uniform:

• Strongest when photosynthesis is Rubisco-limited (high light, moderate temperatures).
• Weaker or saturated under RuBP regeneration limitation, severe nutrient deficiency, drought (though water savings help), or sink limitations.
• Interactions with warming can enhance or offset benefits depending on species and conditions.
• Nutrient dilution (e.g., lower protein/mineral concentrations in tissues) can occur.
• Long-term ecosystem responses depend on soil nutrients, competition, and mortality rates.

In summary, the CO2 fertilization effect primarily arises from enhanced Rubisco carboxylation and reduced photorespiration, combined with stomatal adjustments that improve water-use efficiency.

These leaf-level processes cascade to greater plant growth and contribute substantially to observed increases in global vegetation greenness and the land carbon sink, though modulated by acclimation and environmental constraints.