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Ideas and Perspectives: Is Shale Gas A Major Driver Of Recent Increase In Global Atmospheric Methane?
Robert W. Howarth, Biogeosciences | August 14, 2019
Methane has been rising rapidly in the atmosphere over the past decade, contributing to global climate change. Unlike the late 20th century when the rise in atmospheric methane was accompanied by an enrichment in the heavier carbon stable isotope (13C) of methane, methane in recent years has become more depleted in 13C.
This depletion has been widely interpreted as indicating a primarily biogenic source for the increased methane. Here we show that part of the change may instead be associated with emissions from shale–gas and shale–oil development. Previous studies have not explicitly considered shale gas, even though most of the increase in natural gas production globally over the past decade is from shale gas. The methane in shale gas is somewhat depleted in 13C relative to conventional natural gas.
Correcting earlier analyses for this difference, we conclude that shale–gas production in North America over the past decade may have contributed more than half of all of the increased emissions from fossil fuels globally and approximately one–third of the total increased emissions from all sources globally over the past decade.
The Roles of Livestock in Developing Countries in North America
Livestock play a significant role in rural livelihoods and the economies of developing countries. They are providers of income and employment for producers and others working in, sometimes complex, value chains. They are a crucial asset and safety net for the poor, especially for women and pastoralist groups, and they provide an important source of nourishment for billions of rural and urban households.
These socio–economic roles and others are increasing in importance as the sector grows because of increasing human populations, incomes and urbanisation rates. To provide these benefits, the sector uses a significant amount of land, water, biomass and other resources and emits a considerable quantity of greenhouse gases.
There is concern on how to manage the sector's growth, so that these benefits can be attained at a lower environmental cost. Livestock and environment interactions in developing countries can be both positive and negative. On the one hand, manures from ruminant systems can be a valuable source of nutrients for smallholder crops, whereas in more industrial systems, or where there are large concentrations of animals, they can pollute water sources.
On the other hand, ruminant systems in developing countries can be considered relatively resource–use inefficient. Because of the high yield gaps in most of these production systems, increasing the efficiency of the livestock sector through sustainable intensification practices presents a real opportunity where research and development can contribute to provide more sustainable solutions. In order to achieve this, it is necessary that production systems become market–orientated, better regulated in cases, and socially acceptable so that the right mix of incentives exists for the systems to intensify.
Managing the required intensification and the shifts to new value chains is also essential to avoid a potential increase in zoonotic, food–borne and other diseases. New diversification options and improved safety nets will also be essential when intensification is not the primary avenue for developing the livestock sector. These processes will need to be supported by agile and effective public and private institutions.
The Role Of Ruminants In Reducing Agriculture's Carbon Footprint in North America
Owing to the methane produced by rumen fermentation, ruminants are a source of greenhouse gas (GHG) and are perceived as a problem.
We propose that with appropriate regenerative crop and grazing management, ruminants not only reduce overall GHG emissions, but also facilitate provision of essential ecosystem services, increase soil carbon (C) sequestration, and reduce environmental damage. We tested our hypothesis by examining biophysical impacts and the magnitude of all GHG emissions from key agricultural production activities, including comparisons of arable– and pastoral–based agroecosystems.
Our assessment shows that globally, GHG emissions from domestic ruminants represent 11.6% of total anthropogenic emissions, while cropping and soil–associated emissions contribute 13.7%. The primary source is soil erosion (1 Gt C y–1), which in the United States alone is estimated at 1.72 Gt of soil y–1. Permanent cover of forage plants is highly effective in reducing soil erosion, and ruminants consuming only grazed forages under appropriate management result in more C sequestration than emissions.
Incorporating forages and ruminants into regeneratively managed agroecosystems can elevate soil organic C, improve soil ecological function by minimizing the damage of tillage and inorganic fertilizers and biocides, and enhance biodiversity and wildlife habitat.
We conclude that to ensure long–term sustainability and ecological resilience of agroecosystems, agricultural production should be guided by policies and regenerative management protocols that include ruminant grazing.