New research suggests rainfall and climate variability may play a larger role in soil carbon increases than land management, raising questions about carbon credit schemes.
Soil carbon has become a central pillar of Australia’s climate policy. Farmers are being encouraged – and in some cases financially rewarded – to increase soil carbon stocks through altered grazing and land management practices.
Carbon credits generated from soil projects are now traded in national and international markets, promoted as part of the solution to climate change. But do these schemes actually deliver additional, reliable carbon sequestration?
Substantial amounts of the world’s terrestrial carbon stores are in the soil. Maintaining appropriate levels of carbon and nitrogen in soils is essential for soil health and agricultural productivity. Yet scientific evidence on how land management affects soil carbon remains mixed, particularly in highly variable climates such as Australia’s.
To help address this uncertainty, we examined soil carbon and nitrogen levels at 50 farm sites in south-central New South Wales, measured 11 years apart (2011 and 2022). The sites represented three grazing regimes: total livestock exclusion, rotational grazing (limited duration grazing up to 45 days annually), and continuous set-stocking. Our findings are published in PLOS ONE.
We found that soil carbon and nitrogen levels increased across all sites over the 11-year period – regardless of how they were managed. Indeed, increases were greatest on continuously grazed sites, and smaller where grazing had been reduced or excluded.
One plausible explanation is rainfall. The 2022 sampling occurred after three consecutive years of above-average rainfall in the study region. In Australia’s highly variable climate, time itself can act as a proxy for weather. Wetter years stimulate plant growth, increasing organic matter inputs into soils. Under such conditions, carbon stocks may rise independently of management interventions.
We also found relationships between vegetation structure and soil properties. Sites with more saplings and greater ground cover tended to have higher soil carbon. This aligns with previous Australian research showing that soils beneath trees are generally more fertile than adjacent open areas. But again, rainfall strongly influences vegetation growth, complicating simple attributions to management.
These findings raise important questions for soil carbon crediting schemes. First, if rainfall and climate variability are major drivers of changes in soil carbon, then credited increases may not be additional – that is, they may not result from the management actions being rewarded. Carbon gains that would have occurred anyway during wet years risk being counted as offsets.
Second, soil carbon gains may not be permanent. Australia is characterised by extreme climatic variability, which is projected to intensify with climate change. Droughts and heatwaves can reduce vegetation inputs and potentially reverse earlier gains in soil carbon. Crediting frameworks must account for the risk of such reversals, yet current systems may underestimate this volatility.
Third, soil carbon changes in our study were statistically significant but relatively small. Detecting genuine management effects required repeated measurement over more than a decade. Many Australian ecosystems, particularly those formerly dominated by temperate woodlands, are slow-changing environments. Robust detection of management-driven change may require long-term, intensive sampling – increasing costs and reducing the economic viability of many projects. If these patterns are typical across other ecosystems, there is a real risk that soil carbon crediting schemes may overestimate the climate benefits they claim.
None of this means soil carbon is unimportant. Healthy soils are vital for agricultural resilience, water retention and biodiversity. Improved land management can yield real ecological benefits. But positioning soil carbon as a large-scale, near-term climate mitigation tool demands rigorous evidence.
Our results suggest that climatic variability may exert stronger control over soil carbon dynamics than grazing management alone. In such a context, carbon markets and policymakers should proceed cautiously. Without robust baselines, long-term monitoring and conservative accounting for climate variability, soil carbon schemes risk overstating their contribution to emissions reduction.
David Lindenmayer
Professor David Lindenmayer is a distinguished Australian scientist and academic, specialising in landscape ecology, conservation, and biodiversity. His research focuses on integrating nature conservation with agricultural production, improving biodiversity conservation in forestry and plantations, and enhancing fire management practices. With over 1000 peer-reviewed papers and 50 books, David is one of the most published ecologists globally. He leads large-scale, long-term research programs in south-eastern Australia. A Fellow of the Australian Academy of Science, he has received numerous prestigious awards, including the ESA Whittaker Award, multiple Eureka Prizes, and the Australian Natural History Medal.
Ben C. Scheele
Dr Ben C. Scheele is a conservation ecologist at The Australian National University whose research examines how species respond to environmental change. His work focuses on threatened species conservation, wildlife disease and biodiversity responses to global change, with particular expertise in amphibians. He also works on sustainability challenges in agricultural landscapes, including soil carbon, grazing management and farm dam biodiversity.
Elle Bowd
Dr Elle Bowd is an ecologist and research fellow at the Fenner School of Environment and Society at The Australian National University. Her research focuses on how forest ecosystems respond to disturbances such as wildfire and logging, including the ecological pathways that drive environmental change. She works on plant and fungal ecology in Australian forests and woodlands and is also involved in collaborative projects with First Nations partners supporting the re-emergence of Indigenous-led cultural burning.
Craig Strong
Associate Professor Craig Strong is a soil and landscape scientist at The Australian National University’s Fenner School of Environment and Society. His research focuses on land management, soil systems and environmental monitoring in agricultural and rangeland landscapes. He works on issues such as soil condition, dust and land degradation, grazing management and the impacts of environmental change on land systems.
Andrew Macintosh
Professor Andrew Macintosh is an environmental law and policy scholar at The Australian National University. His research examines environmental governance, climate policy and biodiversity protection, including the regulation of carbon offsets and environmental impact assessment in Australia. He is widely recognised as an expert on land-sector carbon abatement and environmental law and has advised governments, corporations and non-government organisations on climate and environmental policy.
Maldwyn J. Evans
Dr Maldwyn J. Evans is an ecologist and statistician with the Long-Term Ecology Group at The Australian National University. His work focuses on long-term ecological monitoring, statistical modelling, and conservation biology. He has contributed to several large-scale and long-running ecological experiments in Australia and internationally, examining how landscapes and biodiversity respond to environmental change.