There’s a strong cultural inclination toward believing in afforestation as a climate action strategy. Intuitively, it makes sense: the proven ability of forests to draw carbon from the atmosphere while providing essential ecosystem services have led to a quick uptake of forestation initiatives. Whether it be individuals hoping to engage in climate action or corporates looking to offset their emissions, afforestation projects have long been touted as the go-to strategy to heal the environment.

However, a recent study has noted thatlarge-scale forestation projects could have unforeseen effects on global climate. It could cause global changes in regional precipitation, temperature, cloud cover and surface wind patterns—complex effects which have not yet been taken into account when drafting policies and formulating climate action plans. The study, published this month in the journal Nature Communications, found that tree plantation drives could influence regional climate and global weather conditions. Large-scale afforestation affects the Earth’s energy balance by altering atmospheric and ocean circulation patterns, both of which help distribute heat across the Earth’s surface.

While the role of deforestation in affecting global climate has been well documented, the researchers conducted climate model simulations that showed how forestation projects—an umbrella term for afforestation and reforestation programs—could have “opposing effects which strengthen, weaken or shift air circulation patterns, ocean currents and convection cells.” Moreover, it adds to a growing body of research that points out how inappropriate design and implementation of reforestation initiatives — that amount to planting the “wrong trees in the wrong places” — could do more harm than good.

As the adverse impacts of the climate crisis become increasingly apparent in a warming world, both national and individual climate action plans have expanded beyond technological solutions to integrate nature-based solutions as well. A prime example of this is carbon offset programs, where organizations offset their carbon emissions by undertaking global climate mitigation projects, the most popular being tree plantations.

Such plantation drives have taken place at dramatic rates in recent years. For example, in 2016, around 50 million saplings were reportedly planted on a single day in India.

Admittedly, the ecological restoration benefits that afforestation offers are immense—from acting as carbon sinks, improving soil fertility and air quality to providing nutrition, conserving biodiversity and supporting livelihoods of local communities.

In the past, scientists have called the effects of planting trees “mind blowing”. In 2019, it was estimated that a global planting programme could remove around one-third of all emissions arising from human activities at the time.

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However, tree-plantation drives have a contentious history. At the local level, afforestation projects have been called outfor failing to adequately respond to community needs and ecological considerations. In India, most tree plantation projects usually fall under the ambit of compensatory afforestation, funded and managed by the Compensatory Afforestation Fund Management And Planning Authority (CAMPA). As per the Forest Conservation Act (1980), any diversion of forest land for non-forest purposes—such as infrastructural projects—must be compensated through such afforestation programs.

However, compensatory afforestation is plagued by a host of problems, including wasteful expenditure and substandard plantations. A 2022 analysis of tree planting data in the state of Himachal Pradesh found that “over half of the state’s budget for tree planting is wasted on plantations that are unlikely to survive and/or are poorly designed to achieve the state’s goal of increasing forest cover.”

The unavailability of land has also posed significant complications, often leading to compensatory afforestation being carried out in states other than the one where forest diversion has taken place. Most recently, PTI reported the Environment Ministry may allow compensatory afforestation to be carried out in neighboring states due to a severe shortage of land in Delhi.

Environmental scientists and activists have repeatedly highlighted how the choice of tree species also plays a crucial role in designing afforestation programs. Concerns have been raised regarding the wider ecological consequences of razing old-growth forests and replacing them with plantations of a single, often commercial tree species.

Old-growth forests are complex ecosystems that mature without external interference, providing a home to rare and endemic biodiversity while simultaneously storing large amounts of carbon. Once felled, these trees release vast amounts of carbon back into the atmosphere. As compensation, non-native trees that might not be suitable to the region are planted in their stead.

“We cut down an old-growth forest, and say that this thickly forested area can be adequately compensated by planting young saplings elsewhere… Looking at it purely from a carbon accounting perspective, the new plantation cannot compensate for the loss of carbon stocks and other ecosystem services provided by old-growth forests in any realistic timeframe,” Manan Bhan, a forest researcher told Mongabay-India.

While poorly designed tree plantations can have severe repercussions on local ecosystems, the recent study shows how they affect global climate patterns as well. Global-scale forestation can lead to the weakening and poleward shift of the air that circulates in Northern mid-latitude regions.

It may also lead to a slowing down of the Atlantic Meridional Overturning Circulation (AMOC), a large system of ocean currents that transport warm surface waters towards the north of the Atlantic Ocean where it cools and sinks. AMOC regulates the circulation of heat, carbon and freshwater, thereby playing a significant role in determining regional climate conditions. A 2021 study published in the journal Nature Climate Change has already pointed to the slowing of the AMOC, suggesting that the circulation system could collapse beyond a certain threshold.

According to the study, forestation could also affect the Hadley cell, “one of the key atmospheric circulation features that redistributes heat and momentum in the climate system.”

While highlighting potential effects of large-scale changes in forest cover, the researchers duly cautioned that the results of the study must not be viewed as an argument against forestation. Instead, the findings indicate how the focus should be placed on effective design—one that takes into consideration how these projects affect the climate in regions far removed from the forested area.

The study then reveals the immense complexity of climate systems, expanding the impact of locally-implemented solutions to a global scenario. Any solutions to the climate crisis, including forestation projects, will have to account for this complexity in both its design and implementation.