Tropical forests, such as those in the Amazon region, Southeast Asia and the surrounding Congo basin in Africa, have one of the highest rates of carbon sequestration per unit area. Without them, global temperatures would already have risen by more than 1°C on average, the research notes.

In addition to that benefit, the work also points primarily to the fact that forests have a direct impact on the places where they are located due to their biophysical constitution. Trees absorb a lot of light from the sun, unlike bare soil or agricultural areas.

In addition, their deep roots are very efficient in transporting water (and energy) to the atmosphere through evapotranspiration, so under the shade of the tree canopy the temperature is often lower than outside. And that has a big impact on the local microclimate around forested areas.

According to co-author Michael Coe, a researcher at the Woodwell Climate Research Center in Massachusetts, this is due to the change in the way sunlight reaches the ground. On a global scale, this affects the Earth's entire atmosphere and warms the planet.

"You basically export that heat around the world when you do that," he said in a video conference interview with SciDev.Net.

"We knew that, this global estimate taking into account the biophysical impact of forest regions was much needed. There are a lot of global studies on carbon stocks, but there was certainly a lot more we should have taken into account, and it was about time someone did that," Coe continued.

According to the study, forests in a range of 2,200 km around the equator have the capacity to cool the planet due to their biophysical characteristics, in addition to their high carbon absorption capacity.

Forests in this region manage to keep the global average temperature 1°C lower than it would be if they did not exist. "Tropical forests are so important because they photosynthesise every day of the year," he said.

Locally, at all latitudes, the study notes, the biophysical impacts of forests "far outweigh their effects on carbon dioxide, promoting local climate stability by reducing temperature extremes at all seasons and all times of the day."

To reach these conclusions, the team of authors worked through an extensive literature review "with field measurements, satellite measurements, numerical simulations and models showing scale changes and why they occur." "We then calculated the impact of forests on carbon dioxide: how much carbon they contain per latitude," explains Coe.

In this way, the team was able to separate the impacts of carbon absorption on global climate from the trees’ biophysical effects.

For Flávia Costa, a researcher at Brazil's National Institute for Amazonian Research (INPA), who was not involved in the study, the research is interesting because it raises a new issue outside of academia field.

"The biophysical aspects of plants are known and used in climate modelling to predict the effects of deforestation, and are standard features obtained from atmospheric gas monitoring towers and important features for understanding the biophysical effects of trees on the energy balance [absorbed and reflected from the Sun]," she told SciDev.Net.

Costa points out that, unlike carbon sequestration balances, the biophysical effects of forests are less prominent in the media and in public policy negotiations; however, the research shows that, depending on the region of the planet, biophysical effects are as or more important than carbon dioxide absorption effects.

"I found it interesting because it shows a geographical perspective on the local, regional and global effects of plant biophysics on temperature," she added. "At the local level, the biophysical effects of trees are much more important than carbon absorption," she continued.

For the planet to also benefit from the biophysical effects of forests on climate, Costa said, it is just as important to avoid cutting down standing forests as it is to reforest them.

Forests "benefit local populations by improving the local climate. We can't just think about paying carbon credits and outsourcing reforestation," says Costa. "Trees are factories for keeping the planet cooler," concluded Michael Coe.

See, Bosques hacen más por el clima que solo capturar carbono