Climate benefits of planting forests might be overestimated

Afforestation will help limit further warming of the planet by soaking up some of the carbon dioxide we pump into the atmosphere. But global climate benefits may be about 15 to 30 percent lower than previous estimates because of other effects, such as trees absorbing sunlight.

“We’re not saying don’t plant trees,” he says. James Weber at the University of Sheffield in the UK. It’s just that the climate benefits aren’t as big as we thought, he says.

The impact of trees depends on what other measures are taken to combat climate change. The more done, the more Benefits of afforestation, as shown by Weber and colleagues. “It’s more positive and more effective if we do other things as well,” he says.

It has long been known that plants can have both heating and cooling effects. In particular, deep vegetation can have a warming effect by absorbing light that would be reflected back into space if no vegetation were present. This effect is strongest where trees replace snow and ice, but It can happen in other situations too.

Plants also release volatile organic compounds into the air. “These are the chemicals that create the smell of the forest,” says the team member. James KingAlso at Sheffield University.

These biogenic compounds can affect climate in several ways. A prime example is that they can react with chemicals in the atmosphere that otherwise react with methane. “So methane hangs around for a long time, and methane is a strong greenhouse gas,” Weber says.

Compounds released by plants can also react with nitrogen oxides to form ozone, another greenhouse gas.

These effects result in overheating. But biogenic compounds can also form aerosol particles that reflect sunlight and thus have a cooling effect.

To get an estimate of the overall impact of afforestation on climate, the team incorporated these processes and others into a climate model where all available land is forested. This means trees in areas that are currently grasslands, for example, but not farmland or built-up areas.

“To our knowledge, this is the first time this has been done on a global scale, and with a comprehensible forest landscape,” says King.

The researchers created two scenarios. in one, Little has been done to combat climate change. In addition to tree planting, when other effects of forests were taken into account, the warming avoided by CO2-absorbing forests was reduced by 23 to 31 percent.

In another, more optimistic scenario, drastic action is taken to reduce further warming. In this case, gray warming was reduced by 14 to 18 percent.

One reason for the difference is to reduce fossil fuel emissions. Will reduce aerosols from air pollution.. In a polluted world, adding more aerosols from forests doesn’t make much of a difference, but in a cleaner world, the cooling effect is greater.

The team acknowledges that the model is still incomplete and does not include all feedback. For example, this includes the greenhouse effect of ozone, but not its effect on plants. High ozone levels Can kill trees., That means less CO2 is released from the atmosphere.. The model also does not include the effect of wildfires.

“It’s very complicated,” says King. “It’s not really possible to consider every single set of feedbacks in one study.”

“Importantly, the study shows that stopping deforestation is a much more effective way of mitigating climate change than deforestation, and should therefore be prioritized,” he says. Stephanie Rowe, Climate scientist at WWF in Washington DC.

There is another missing expression in the model. Cooling effect of water evaporating from leaves, says Roe, which can grow in tropical areas. She says that while the climate benefits of forests may be overestimated, the study still doesn’t give the full picture.

Furthermore, forests have numerous other benefits for people and wildlife, including reducing erosion, maintaining water supplies and water quality, providing food and jobs, Reducing local heat extremes and more. “Forests, and especially reforestation with native species in forest biology, is absolutely worth pursuing,” Rowe says.

“We’ve always known that forests have warming effects under certain conditions and cooling effects under others. What this study shows is that the overwhelming net effect of forests is cooling,” he says. are Thomas Crowther On ETH Zurich in Switzerland.

“But most importantly, even if they don’t have such a chilling effect, we still need to protect natural forests to support Earth’s biodiversity and the billions of people who depend on them.”