Two new reports take a closer look at the link between human activities and increased greenhouse gas emissions.
The first, a study coming from researchers at the University of Michigan and Tulane University, found that on any given day, 20 percent of Americans account for nearly half of U.S. diet-related greenhouse gas emissions, and high levels of beef consumption are largely responsible,
To estimate the impact of U.S. dietary choices on greenhouse gas emissions, the researchers built a database that assessed the environmental impacts involved in producing more than 300 types of foods. Then they linked the database to the findings of a nationally representative, one-day dietary recall survey involving more than 16,000 American adults.
They ranked the diets by their associated greenhouse gas emissions, from lowest to highest, then divided them into five equal groups, or quintiles. The researchers found that the 20 percent of U.S. diets with the highest carbon footprint accounted for 46 percent of total diet-related greenhouse emissions.
The highest-impact group was responsible for about eight times more emissions than the lowest quintile of diets. And beef consumption accounted for 72 percent of the emissions difference between the highest and lowest groups, according to the study.
Source: Michigan News
The second, a “Greenhouse Gas Bulletin” report from World Meteorological Organization, indicated that the abrupt changes in the atmosphere witnessed in the past 70 years are without precedent. The report noted that concentrations of carbon dioxide in the atmosphere surged at a record-breaking speed in 2016 to the highest level in 800,000 years.
Robert Howarth, Cornell professor of ecology and evolutionary biology and an expert on the atmospheric implications of methane, said while some researchers have concluded that cattle are the cause of the increase, shale gas and shale oil are most likely the reasons behind the steep climb.
“Several papers over the past 18 months have concluded that fossil fuels may not be the cause of the latest surge in methane. However, there is very strong evidence that these papers are wrong,” Howarth said. “Several of the papers have concluded that an increase in emissions from cows and cattle is the cause. This conclusion conflicts strongly with the satellite data, which show that the increase in global methane emissions over the past decade has come mostly from the U.S.; numbers of cows and cattle have decreased in the U.S. over this decade, and so this cannot be the cause…
“Note that the papers indicating that cows are the culprit are basing their conclusions on the stable carbon (C13) isotopic composition in the atmosphere, but they have all missed some fundamental literature that shows that this value for methane from shale gas sometimes looks more like methane from cows than it does methane from conventional natural gas. That is, they may have made a fundamental flaw,” Howarth concluded.