Tropical Trees Beat Northern Forests for Cooling Planet

Researchers at ETH Zurich just solved a puzzle that could transform how we fight climate change: location matters more than quantity when planting trees.

Using one of Europe's most powerful supercomputers, scientists analyzed three global reforestation scenarios and found something remarkable. Two plans delivered identical cooling effects even though one required 450 million extra hectares of land. That's an area the size of the entire European Union.

The secret lies in tropical forests. Trees planted in the Amazon Basin, West Africa, and Southeast Asia provide the strongest climate benefits because they do double duty. They store carbon like all trees, but they also cool the air through evapotranspiration, where water released from leaves lowers local temperatures.

Lead researcher Nora Fahrenbach and her team ran their climate model five times over four months, generating 300 terabytes of data to confirm the findings. The simulations tracked not just carbon absorption but also how forests change Earth's surface by reflecting sunlight and altering water evaporation.

Northern forests in places like Siberia and Canada sometimes warm their surroundings instead of cooling them. Snow-covered ground reflects sunlight back to space, but when dark tree canopies replace that snow, they absorb heat instead. This creates a net warming effect that cancels out the carbon benefits.

The Bright Side

This discovery means climate projects can achieve their goals while preserving land for other uses. Focusing reforestation efforts in tropical regions makes every hectare count, turning tree planting from a numbers game into a strategic tool.

The research arrives as global initiatives like the UN Environment Programme and Trillion Tree Campaign work to restore forests worldwide. Earlier estimates suggested reforesting up to 1,000 million hectares could absorb 750 gigatonnes of carbon dioxide, but those calculations used simplified models that missed important real-world factors.

The ETH Zurich team used an advanced Earth-system climate model that captures interactions between atmosphere, oceans, and land surface. They tested scenarios from 2015 to 2070, excluding urban areas, glaciers, and most agricultural land to keep projections realistic.

"The fact that we can achieve the same cooling effect with significantly less land shows that where we plant is more important than how much we plant," Fahrenbach explained.

Smart geography could make reforestation a far more efficient climate solution without requiring impossible amounts of space.