Methane and nitrous oxide found in human exhalations are worse for the environment than carbon dioxide, scientists say
Human breathing contributes to global warming, according to a study published Wednesday in PLoS One. The authors argued that human respiration’s contribution to climate change has been underestimated and merits further study.
After measuring the gas composition in the exhaled breaths of 328 study participants, the researchers concluded human breath comprises 0.05% of the UK’s methane emissions and 0.1% of its nitrous oxide. Both of those gasses “have a much higher global warming potential than carbon dioxide,” the study notes.
“Exhaled human breath can contain small, elevated concentrations of methane (CH4) and nitrous oxide (N2O), both of which contribute to global warming,” the researchers, led by atmospheric physicist Nicholas Cowan of the UK Centre for Ecology and Hydrology, wrote. “We would urge caution in the assumption that emissions from humans are negligible.”
While Cowan explained that “CO2 contribution in human breath to climate change is essentially zero” because plants absorb nearly all the carbon dioxide humans breathe out, the other two gasses are left in the atmosphere. Methane traps 80 times the amount of heat as carbon dioxide during its first 20 years in the atmosphere, though this potency decreases over time.
A detailed analysis of test subjects’ diets failed to yield any indication that meat eaters produced more of either gas. While all test subjects exhaled nitrous oxide, only 31% exhaled methane. These individuals, referred to as “methane producers” in the paper, were more likely to be female and over 30 years of age, though the researchers were unable to determine why this was the case.
The study authors cautioned that their research only looked at breath and called for further research into the total picture of human gas emissions, insisting it could reveal more about the “impacts of an aging population and shifting diets” on the planet.
In recent years, environmental campaigners have focused on methane emissions from cows, whose herbivorous diet is broken down by methane-producing bacteria in their multiple stomachs. Policymakers’ focus on the resulting methane-tainted belches and farts have been the subject of much parody from climate change skeptics.
The UK has legally committed itself to reducing greenhouse gas emissions by 78% by 2035 compared to 1990. Residents have been strongly encouraged to reduce meat consumption in order to achieve this goal, with some estimates placing the share of global greenhouse gas emissions from raising livestock for meat at 15%. However, the researchers behind Wednesday’s study pointed out that shifting to a high-fiber vegetarian diet could potentially cause more methane and nitrous oxide emissions, a phenomenon they called “pollution swapping.”
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