Study: forests help make Earth cooler

Chinese scientists have recently discovered that forests not only sequester carbon, but also form a natural cooling barrier by releasing key substances, amplifying the climate benefits of afforestation.

Led by Fu Pingqing, a professor from Tianjin University, the research highlights how China's reforestation efforts under its carbon neutrality strategy could deliver enhanced cooling effects against global warming. The findings were published in Nature Geoscience recently.

Previous research established that natural vegetation areas such as forests emit volatile organic compounds. According to Zhu Jialei, a core team member at Tianjin University, these VOCs serve as raw materials for secondary organic aerosols.

"SOA particles in the atmosphere effectively reflect solar radiation and modify cloud properties, functioning like a 'cooling umbrella' for Earth," Zhu explained. This dual role makes forests not just Earth's lungs for carbon absorption, but also critical natural air conditioners.

Since the Industrial Revolution, global cropland area has expanded by approximately 270 percent, causing significant shrinkage of forests and grasslands. Zhu's team developed a proprietary aerosol module to upgrade Earth system models, enabling the first precise quantification of historical cropland expansion and its impact on SOAs and cooling effect.

The study revealed that cropland expansion reduced global SOA levels by around 10 percent, weakening their net cooling effect by about 11 percent.

"Forests act as nature's cooling barrier. Replacing them with farmland diminishes this protective function," said Zhu.

This occurs because agricultural crops emit far fewer VOCs and generate less SOAs than forest trees. Consequently, cropland expansion disrupts the Earth's natural cooling mechanism, contributing significantly to global warming.

This pivotal finding, based on two years of research building on a decade of SOA studies, fills critical knowledge gaps regarding land-use changes, organic aerosols and climate interactions, with profound policy implications.

China has achieved remarkable progress in afforestation, boasting the world's largest artificial forest area. The Three-North Shelterbelt Program, China's flagship ecological project and the largest restoration initiative in the world, spans over 4 million square kilometers, creating ecological security barriers across North, Northeast and Northwest China.

The research confirms that China's afforestation not only absorbs carbon dioxide, but also reinforces Earth's "natural cooling" capacity, delivering dual climate dividends.

"It demonstrates how China's carbon neutrality strategy, especially large-scale afforestation, constitutes a major contribution to global climate action, showcasing China's responsibility for environmental protection," Zhu emphasized.

The Tianjin University-led study involved collaboration with Tsinghua University and the University of Michigan in the United States. Sino-US scientific cooperation enabled breakthroughs in Earth system modeling and land-use change scenario design.

"Joint research with US scientists accelerated our progress, positioning this work at the global forefront," Zhu noted.

Zang Yifan contributed to this story.