A new NASA-sponsored study shows that global methane emissions produced by livestock are 11 per cent higher than estimates made last decade. Because methane is a particularly nasty greenhouse gas, the new finding means it's going to be even tougher to combat climate change than we realised.
We've known for quite some time that greenhouse gases produced by cattle, sheep and pigs are a significant contributor to global warming, but the new research, published in Carbon Balance and Management, shows it's worse than we thought. Revised figures of methane produced by livestock in 2011 were 11 per cent higher than estimates made in 2006 by the Intergovernmental Panel on Climate Change (IPCC) -- a now out-of-date estimate.
It's hard to believe that belches, farts and poop from livestock could have any kind of global atmospheric effect, but it's an issue of scale, and the nature of methane itself.
There are approximately 1.5 billion cows on the planet, each and every one of them expelling upwards of 110 to 190L of methane each day. We typically think of farts as being the culprit, but belches are actually the primary source of cattle-produced methane, accounting for 95 per cent of the problematic greenhouse gas.
And problematic it is. Methane is about 30 times more efficient at trapping the Sun's radiative heat than carbon dioxide over a timescale of about a century. There may be more CO2 in the atmosphere than methane, but by unit, it's the more destructive greenhouse gas. Both NASA's Carbon Monitoring System research initiative and the Joint Global Change Research Institute (JGCRI) contributed to the study.
Wolf's team re-evaluated the data used to produce the IPCC 2006 methane emissions estimates. The prior estimates were based on relatively modest rates of methane increases from 2000 to 2006, but things changed dramatically afterwards, increasing 10-fold over the course of the next 10 years. The new figures factor an 8.4 per cent increase in methane emissions from digestion (otherwise known as "enteric fermentation") in dairy cows and other cattle, and a 36.7 per cent increase in methane from manure, compared to previous IPCC-based estimates. The new report shows that methane accounted for approximately 16 per cent of global greenhouse gas emissions in 2016. Other human activities, such as the production and transport of gas, oil and coal, along with the decay of our organic waste, also contribute to global methane emissions.
Importantly, the new estimates are 15 per cent higher than global estimates produced by the US Environmental Protection Agency (EPA), and four per cent higher than EDGAR (Emissions Database for Global Atmospheric Research).
"In many regions of the world, livestock numbers are changing, and breeding has resulted in larger animals with higher intakes of food," noted Wolf in a release. "This, along with changes in livestock management, can lead to higher methane emissions." To which she added: "Direct measurements of methane emissions are not available for all sources of methane. Thus, emissions are reported as estimates based on different methods and assumptions. In this study, we created new per-animal emissions factors -- that is measures of the average amount of CH4 discharged by animals into the atmosphere -- and new estimates of global livestock methane emissions."
The new research shows that methane emissions slowed in the US, Canada and Europe, but they're rising elsewhere. Very likely, the rest of the world is catching up to first-world standards in terms of meat and dairy consumption.
"Among global regions, there was notable variability in trends in estimated emissions over recent decades," said Ghassem Asrar, Director of JGCRI and a co-author of the new study. "For example, we found that total livestock methane emissions have increased the most in rapidly developing regions of Asia, Latin America and Africa... We found the largest increases in annual emissions to be over the northern tropics, followed by the southern tropics."
It's not immediately clear how, or even if, these revised figures will impact livestock production or public policy, but at the individual level, it suggests we should cut back on our consumption of meat and dairy. The privilege we have over these animals, it would appear, now comes at a hefty price.