A group of international researchers has come to the surprising conclusion that reforesting the entire tropical regions of Earth would have an almost negligible effect on atmospheric carbon dioxide.
In their paper, the scientists from London, Leeds and Hong Kong, wanted to test an extreme hypothetical scenario involving the reforestation of vast areas of land in Brazil, DR Congo, India and Indonesia, among other areas.
Trees, forests and rainforests factor heavily into many long-term climate change mitigation strategies. However, they cannot and should not be examined in isolation and must be viewed alongside soil, oceans and other parts of the planetary ecosystem when it comes to avoiding climate catastrophes in the future, the researchers say.
Once you consider those factors, tree planting is “not as potent a solution as it may first seem,” and the latest research once again highlights the complexity of balancing Earth’s climate and atmosphere.
Using the UK Met Office’s climate change model, a computer simulation which factors in oceanic, land and climate interactions, the researchers chose the tropics as they foster the fastest tree growth.
They then simulated two futures: one in which serious governmental action across the planet was undertaken to avoid surpassing the two degrees Celsius temperature threshold agreed in the Paris Climate Accord, while the second scenario was identical but all farming across the tropics was also stopped, allowing vegetation and forests to recover.
The models found that the new tropical megaforests would store an extra 124 billion tons of carbon by 2100, roughly the equivalent of 13 years’ worth of fossil fuel emissions at the 2021 rate.
Crucially, however, the atmospheric carbon in this scenario – which is what matters when it comes to climate change – would only drop by 18 billion tons, or the equivalent of two year’s worth of 2021 fossil fuel emissions.
To their dismay, the researchers found that, with these new tropical forests picking up more of the carbon-absorbing slack, other parts of Earth’s ecosystem would absorb less. “If the tropics were reforested, our model predicts that the oceans, soil and vegetation would absorb less carbon dioxide,” they write.
The main reason behind this discrepancy is the fact that the turnover of dead plants within tropical forest soils is much slower than the equivalent plant loss and decay on agricultural land.
In addition, the reduction of atmospheric carbon dioxide by these new tropical mega-forests would slow plant growth elsewhere in the world, resulting in reduced carbon capture and storage in soils outside of the tropics.
The researchers found that, ultimately, reforesting the tropics, while accounting for the changes in soil, vegetation and ocean carbon absorption, would result in just a 10-parts-per-million atmospheric carbon dioxide reduction.
“The Earth system starts to work against us when we plant trees or use other methods of removing atmospheric CO2,” the researchers write, concluding that while their findings are “sobering,” they also highlight “that the best way to avoid dangerous global heating is by not releasing fossil carbon into the atmosphere in the first place.”
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