Rising Atmospheric CO₂ and Its Impacts on Plants

Research indicates that the Earth has been undergoing a greening trend for nearly four decades, impacting half of the world’s vegetated regions due to the effects of CO2 fertilisation. Browning or decrease in greening is also observed in around 4% of the global vegetated area.

A 2016 paper published in Nature, “Greening of the Earth and its drivers“, found that leaf growth or greening increased in up to 50% of the vegetated areas on Earth due to CO2 fertilisation from rising atmospheric CO₂ due to human activity.

This greening trend is observed across Australia, central Africa, the Amazon Basin, the southeast United States, and Europe. At the same time, only a small portion, less than 4%, showed a decrease or browning in northwest North America and central South America. They attribute this browning trend to the long-term and cumulative use of nitrogen fertilisers. While nitrogen in soils can promote greening, excessive amounts can have the opposite effect.

Using long-term satellite data and global ecosystem models, the study finds that the greening results from increased atmospheric carbon dioxide, accounting for approximately 70% of the change. Other contributors include nitrogen from pollution (9%), climate change (8%), and changes in land use (4%). CO2 had the most significant impact in tropical regions, while climate change led to increased greening in colder areas, such as the high latitudes and the Tibetan Plateau.

Meanwhile, the greening trends in southeast China and the southeastern United States, although accounting only for a small percentage of the global greening trend, result from land management, as both regions practice intensive cropping and reforestation.

The authors’ findings demonstrate that the greening or browning of vegetated areas worldwide is convincing proof of human influence on the planet. The study notes that this greening can remove more CO2 from the atmosphere, slowing climate change.

However, the authors also caution that the positive impact of greening is overshadowed by the adverse effects of extreme weather events, such as droughts, heatwaves, floods, sea level rise, and ocean acidification, all caused by climate change.

Another study published in January 2023 shows that greening could offset the warming caused by climate change. The study, “Biophysical impacts of earth greening can substantially mitigate regional land surface temperature warming,” shows that greening slightly cools the planet overall.

However, the effect varies by location and season. Snow cover, plant growth, and sunlight are key factors that influence how strong this cooling effect is. On average, the global surface cooled by about 0.018°C per decade due to greening, which has helped slow global warming by around 4.6%.

This cooling effect is much more substantial in some regions, like India and China, offsetting up to 39% of warming in India and 19% in China. The authors suggest that the cooling influence of vegetation should be included when planning for climate change at the local level.

Is the Earth’s greening caused by carbon emissions a good thing? Will this mitigate the impacts of climate change?

Other studies suggest that while greening offers benefits due to increased CO2 concentrations in the atmosphere, it also has some adverse effects. For instance, greening only offsets around 5% of the warming from carbon dioxide emissions. A 2018 study suggests that rising carbon dioxide levels in the atmosphere could alter the nutrient content of rice, potentially impacting up to 2 billion people who rely on rice as their primary food source.

A 2022 article from the State of the Planet illustrates how increased CO2 emissions can impact plants, citing findings from relevant studies. On the other hand, increased levels of CO2 in the atmosphere lead to enhanced plant growth, both above ground and below ground. 

Elevated CO2 concentrations enable plants to use less water, allowing more moisture in the soil and waterways. However, increased CO2 levels can also affect how plants absorb nitrogen, potentially leading to decreased productivity. Rising temperatures contribute to longer and warmer growing seasons, resulting in greater plant water demand and potentially drier soils.

Additionally, milder winters and extended growing seasons can benefit pests, pathogens, and invasive species threatening vegetation. Furthermore, rising temperatures can induce plant stress, ultimately leading to crop losses.

Climate change also leads to more frequent and severe extreme weather events, including intense precipitation, wind disturbances, heat waves, and droughts.

While greening has benefits, it also comes with negative impacts from climate change. Fortunately, ongoing research will continue to illuminate the complex interactions between plant physiology, behaviour, and the effects of climate change.

Please browse the sources below to learn about how climate change affects plants.