By Sharon Atieno

Despite the important role of grasslands in animal forage, biodiversity and ecosystem services; human activities are causing grasslands to become a source of greenhouse gas emissions rather than a carbon sink, new study reveals.

The study published in Nature Communications, quantifies the changes in carbon storage and greenhouse gas fluxes in natural and managed grasslands between 1750 and 2012.

It finds that the ability of grasslands to absorb more carbon and pack it in the soil intensified over the last century but mainly over sparsely grazed and natural grasslands.

Conversely, the study shows that over the last decade, grasslands intensively managed by humans have become a net source of greenhouse gas emissions, with levels similar to that of global croplands, which represent a large source of greenhouse gases.

Further, it finds that emissions of methane and nitrous oxide almost tripled since 1750 due to increased emissions from livestock that have more than compensated for reduced emissions from the shrinking number of wild grazers.

“Our results show that the different human activities that have affected grasslands have shifted the balance of greenhouse gas removals and emissions more towards warming in intensively exploited pastures, and more towards cooling in natural and semi-natural systems. Coincidently, until recently the two types of grasslands have almost been canceling each other out,” notes coauthor Thomas Gasser from the International Institute for Applied Systems Analysis (IIASA) in a statement.

“However, the recent trends we see towards the expansion of pasture land and higher livestock numbers lead us to expect that global grasslands will accelerate climate warming if better policies are not put in place to favor soil carbon increases, stop deforestation for ranching, and develop climate-smart livestock production systems.”

According to the authors, the cooling services provided by sparsely grazed or wild grasslands, makes it clear that countries should assess not only the greenhouse gas budgets of their managed pastures (such as specified in the current national greenhouse gas reporting rules of the UN’s Framework Convention on Climate Change), but also the sinks and sources of sparsely grazed rangelands, steppes, tundra, and wild grasslands.

“In the context of low-warming climate targets, the mitigating or amplifying role of grasslands will depend on a number of aspects. This includes future changes in grass-fed livestock numbers; the stability of accumulated soil carbon in grasslands; and whether carbon storage can be further increased over time or if it will saturate, as observed in long-term experiments,” concludes Philippe Ciais, a study coauthor from the Laboratory for Sciences of Climate and Environment (LSCE).