Uncovering how grasslands changed our climate
https://phys.org/news/2021-01-uncovering-grasslands-climate.html
https://www.nature.com/articles/s41467-020-20406-7#auth-Victoria-Naipal
Grasslands are managed worldwide to support livestock production, while remaining natural or semi-natural ones provide critical services that contribute to the wellbeing of both people and the planet. Human activities are, however, causing grasslands to become a source of greenhouse gas emissions rather than a carbon sink. A new study published in Nature Communications reports how grasslands used by humans have changed our climate in recent centuries.
Grasslands are the most extensive terrestrial biome on Earth and are critically important for animal forage, biodiversity and ecosystem services. They absorb and release carbon dioxide (CO2), and emit methane (CH4) from grazing livestock and nitrous oxide (N2O) from soils, especially when manure or mineral fertilizers are introduced. Little is known, however, about how the fluxes of these three greenhouse gases from managed and natural grasslands worldwide have contributed to climate change in the past, or about the role of managed pastures versus natural or very sparsely grazed grasslands.
To address this knowledge gap, an international research team quantified the changes in carbon storage and greenhouse gas fluxes in natural and managed grasslands between 1750 and 2012. The study's comprehensive estimates of global grasslands' contribution to past climate change illustrate the important climate cooling service provided by sparsely grazed areas, and the growing contribution to warming from quickly increasing livestock numbers and more intensive management, which are associated with more CH4 and N2O emissions in determining the contemporary net climate effect of the grassland biome.
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from grasslands increased by a factor of 2.5 since 1750 due to increased emissions from livestock that have more than compensated for reduced emissions from the shrinking number of wild grazers. The net carbon sink effect of grasslands worldwide—in other words, the ability of grasslands to absorb more carbon and pack it in the soil—was estimated to have intensified over the last century, but mainly over sparsely grazed and natural grasslands. Conversely, over the last decade, grasslands intensively managed by humans have become a net source of greenhouse gas emissions—in fact, it has greenhouse gas emission levels similar to those of global croplands, which represent a large source of greenhouse gases
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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