The Carbon Fertilisation Effect
For decades, scientists have understood a phenomenon known as the 'carbon fertilisation effect'. In simple terms, when there is more carbon dioxide (CO2) in the atmosphere, plants can perform photosynthesis more efficiently. Photosynthesis is the process
where plants use sunlight, water, and CO2 to create their own food—sugars for energy and growth. With more CO2 available, many plants can produce these sugars faster. It is like offering a chef more of a key ingredient. The process becomes more productive. Studies have shown that this effect has led to a significant 'greening' of the planet, with increased plant growth observed in many regions across the globe. This has been a crucial buffer against climate change, as plants absorb roughly 30% of the CO2 emitted by human activities each year, helping to slow the rate of warming.
A Surprising Boost in a Warmer World
Recent studies are refining this picture, suggesting that under certain conditions, the ability of plants to absorb CO2 may be even more robust than many climate models predicted. Some research indicates that as CO2 levels rise, plants can partially close the tiny pores on their leaves, called stomata. These pores are where CO2 enters, but they are also where water escapes through a process called transpiration. By narrowing these openings, plants can take in the CO2 they need while losing less water—a crucial advantage in a warming world. This increased water-use efficiency could mean that even under moderate drought conditions, some crops might fare better than expected, partially offsetting the negative impacts of water scarcity. It’s a fascinating display of natural adaptation, where plants adjust their own physiology to make the most of a changing environment.
The Hidden Costs of Overdrive
However, this is where the good news ends. The same mechanism that helps plants save water can backfire spectacularly. When plants reduce transpiration, they also reduce their ability to cool themselves. Transpiration works like sweating does for humans; the evaporation of water from the leaves dissipates heat. When this cooling process is reduced, leaves can overheat, especially during heatwaves. This can damage the enzymes essential for photosynthesis, leading to a rapid decline in the plant's health and even death. Furthermore, the benefits of CO2 fertilisation are often cancelled out when heat and drought become extreme. Recent studies have shown that intense heatwaves can severely reduce or even reverse the ability of ecosystems to act as carbon sinks. A 2022 heatwave in Europe, for instance, slashed the carbon absorption capacity of local vegetation by 27%.
What This Means for India
For India, these findings are particularly resonant. Our nation is on the front lines of climate change, experiencing increasingly frequent and intense heatwaves and erratic monsoon patterns. Our agriculture is a complex mix, with some regions being rainfed and others heavily reliant on irrigation. The idea that crops like wheat could become more water-efficient might seem like a silver lining. However, the risk of concurrent heat and moisture stress is immense. The potential gains from CO2 fertilisation could be entirely wiped out by a single prolonged drought or a scorching heatwave during a critical growing stage, leading to crop failure and threatening food security. Our forests, from the Himalayas to the Western Ghats, are also at risk. While they are vital carbon sinks, the increased stress from a warmer, drier climate could compromise their ability to absorb carbon and even lead to greater forest fire risk.
A Fragile Balancing Act
The latest research paints a complex and, at times, contradictory picture. Some studies highlight that increased photosynthesis does not always translate into long-term carbon storage in wood, a process crucial for mitigating climate change. Trees may absorb carbon but use it for short-lived processes like producing leaves rather than locking it away in their trunks. Moreover, the entire 'fertilisation effect' depends on the availability of other nutrients like nitrogen in the soil, which is often a limiting factor that many climate models have overestimated. Ultimately, the consensus is clear: while plants are showing remarkable physiological flexibility, they are also under immense strain. We cannot treat them as a get-out-of-jail-free card for climate change. Their increased absorption of carbon is not a solution but a symptom of an overloaded global system.
