Biodiversity loss and land degradation are intensifying climate change, a UN report says.
Key ecosystems are shifting from absorbing carbon to releasing it.
Parts of the Amazon face irreversible change if climate tipping points are crossed.
Soil and peatland degradation is driving significant greenhouse gas emissions.
Invasive species, air pollution and warming are accelerating ecological decline.
Loss of biodiversity and land degradation driven by human activity are increasingly disrupting the climate system, triggering atmospheric changes that in turn accelerate further ecological damage, according to the latest Global Environment Outlook report.
The Global Environment Outlook-7 (GEO-7), published on December 9, 2025 by the UN Environment Programme (UNEP), said biodiversity loss affects the climate system primarily through its influence on nitrogen, carbon and water cycles. For example, research shows that the fertilising effect of rising atmospheric carbon dioxide linked to deforestation has increased water-use efficiency in boreal forests.
However, ecosystems respond unevenly to environmental stress, adopting different adaptive strategies with varying outcomes, the report stated.
Despite overall net carbon emissions from deforestation and land degradation remaining broadly stable over the past two decades, the report found that the Amazon — the world’s largest tropical forest and a critical carbon sink — is showing signs of decline due to deforestation, rising temperatures and increasing moisture stress.
This trend is particularly pronounced in eastern Amazonia during the dry season. “An estimated 10 to 47 per cent of the Amazon’s forests are exposed to a combination of warming temperatures, extreme droughts, deforestation and wildfires,” the report said. “Which could result in an irreversible ecosystem transition if certain critical thresholds or tipping points are crossed, potentially exacerbating regional climate change.”
In south-east Asia, both bottom-up and top-down models show that the region’s net carbon sink approaches zero between October and December. The report adds that extreme global heat in 2023 is expected to have caused a gross carbon loss of 1.73 gigatonnes across terrestrial ecosystems worldwide, signalling a substantial weakening of land systems as carbon sinks.
Biodiversity loss and land degradation also influence climate by altering the Earth’s surface reflectivity, or albedo. Darker forest cover can increase heat absorption, creating positive radiative forcing that reduces the cooling benefits of carbon sequestration. As a result, the report notes, reducing deforestation in high-latitude regions could in some cases increase warming.
Soils play a critical role in the global carbon cycle. The report notes that global soil carbon stocks are more than three times greater than the combined carbon content of the atmosphere and biosphere, with the potential to sequester nearly 2,500 gigatonnes of carbon dioxide. This positions soil as a vital component in climate regulation.
However, changes in land use and land cover — compounded by fossil fuel use and biomass burning — are altering carbon fluxes and reserves, threatening the long-term viability of ecosystem services at both regional and global scales.
Soil emissions are estimated to contribute between 6.8 and 7.9 gigatonnes of carbon dioxide equivalent to the atmosphere. These emissions largely comprise methane from undisturbed peatlands and rice cultivation, nitrous oxide from managed and unmanaged soils, and carbon dioxide from land-use change.
Indonesia, China and Russia together account for about 31 per cent of global peatland-related carbon emissions. The report also links mangrove loss and declining organic carbon — indicators of land degradation — to rising emissions.
Climate shifts and the spread of invasive species are further accelerating biodiversity loss. The report cites the detection of invasive species in terrestrial and freshwater ecosystems in the Antarctic and Southern Ocean region, where about 13 per cent of species are now considered locally invasive.
Changes in species distribution are also evident. Himalayan birch (Betula utilis), for example, is increasingly shifting eastwards across the Himalayas, while populations decline in the west.
“In California, nitrogen deposition, climate-change-driven plant invasions, high carbon dioxide concentrations and fire interact in complex ways to reshape ecosystems,” the report says. Invasive annual grasses have created new fire regimes in desert areas, producing harmful ecological effects and reinforcing a destructive grass–fire cycle.
Air pollution is also contributing to biodiversity loss. Tropospheric ozone — a secondary air pollutant — damages vegetation and reduces species diversity. In 2020, ozone levels exceeded critical thresholds for forest protection across 59 per cent of forested areas in the 32 member countries of the European Environment Agency. Although exposure of agricultural land to harmful ozone declined between 2000 and 2020, it still affected 6 per cent of farmland in 2020.
The impacts extend beyond forests and soils. Snow-covered regions are increasingly affected by extreme heat, leading to reduced snowfall and faster snowmelt. This exposes ground vegetation and wildlife to ultraviolet radiation earlier in the spring.
“When black carbon, which absorbs solar radiation, is deposited on snow-covered mountains, the heat released accelerates snowmelt,” the report said, highlighting yet another feedback loop intensifying climate and ecological change.