Research by leading greenhouse gas experts Dr Andy Reisinger and Dr Harry Clark of the NZ Agricultural Greenhouse Gas Research Centre found livestock emissions directly contributed at least 23% of total global warming in 2010.
It was a figure Reisinger described as being clearly significant and the sector had to be part of a global effort to reduce emissions.
As carbon dioxide emissions from coal-fired energy generation and fossil-fuelled transport were dealt with the world would turn to its attention to methane management.
One argument was that because methane lasted only 12.4 years in the atmosphere, compared to carbon dioxide which lasted for hundreds or thousands of years, it should not be given the same priority in terms of mitigation.
Emissions of different greenhouse gases were typically compared by what was called their global warming potential, which considered both their efficacy at absorbing heat radiation and their lifetime in the atmosphere.
But Reisinger said there were a lot of assumptions in such calculations and it could be argued its global warming potential overstated its significance in NZ’s emission profile.
In particular, the argument went that because of the short lifetime of methane, its emissions did not have to decline to zero for the climate to stabilise and that reduced the significance of agriculture’s contribution to global warming.
However, the research bypassed that debate and used a simple climate model to understand how much methane and nitrous oxide from livestock contributed to warming.
“What we found was that of the warming the world experienced by 2010, as much as 19% was due to direct historical methane and nitrous oxide emissions from livestock.
“Once you add the warming due to emissions when land is converted to pastures, you end up with a total contribution of 23% to current warming,” Reisinger said.
That figure did not include emissions from energy use or growing livestock supplements so could be taken as the lower end of its contribution.
The implications of business-as-usual livestock farming continuing would increase the agricultural emissions contribution another 15% by 2030 and an extra 30% by 2050.
That increase would be a lot less than the expected increase in demand for livestock products and already implied a significant global increase in the productivity and efficiency of livestock systems.
If all sectors continued to increase emissions unabated the world would warm by 4C.
Farmers would find some small comfort in knowing livestock would be making a declining contribution to that ever-growing emissions cloud.
If temperatures rose 4C by 2100 livestock would be contributing only 5% of the warming, compared to the 23% today.
That relative decline in livestock’s contribution was because if no efforts to reduce emissions in any sector were made, carbon dioxide from the ongoing use of fossil fuels would be by far the biggest source of future warming.
“In other words if the world goes to hell in a hand basket, it won’t be because of livestock.”
But if all sectors reduce their emissions as much and as quickly as possible the increase in temperatures could be limited to less than 2°C.
That meant reducing net emissions of carbon dioxide to zero by about 2050 and subsequently removing carbon from the atmosphere as well as making major reductions in emissions of other greenhouse gases.
Given the tight timeframes laid out in the Paris Accord, any extra reductions that could be achieved with methane would increase the wriggle room, albeit very slightly, for the Herculean effort required to phase out carbon dioxide.
Halving livestock methane emissions by the year 2100 would increase the carbon budget (the amount of carbon dioxide that could be emitted to keep temperature rise under 1.5C as agreed at Paris) by as much as about a third.
“That is a significant contribution.”
“We know now that we have to get carbon dioxide to zero by about 2050 if we want to meet the Paris goals, no ifs or buts about that.
“But as methane does not have to get to zero for the climate to stabilise, people rightly ask whether we should reduce its emissions at all and you can see that argument already playing out in NZ.
“Our study makes clear methane does contribute to global warming and reducing methane would reduce global warming and this would make it more likely that the world can meet its ambitious goals of limiting global warming to less than 2°C.”
Reisinger said determining gas reduction from the livestock sector brought some challenges and ultimately moral questions with it.
NZ was regarded as a low intensity emitter.
It could be argued if NZ reduced production while world demand was rising then production simply moved to a less efficient country, with NZ’s economy suffering, global emissions rising and both the world and NZ ultimately worse off.
“In fact, viewed from this angle, NZ should not worry at all about its emissions but only about minimising its emissions intensity and efficiency of production.
“On the other side is the view is that livestock production contributes significantly to global warming and that this is simply not acceptable for NZ, given that climate change is a major problem.
“The consequence of that position is that we need to consider not only ways to reduce emissions from livestock systems but also consider viable, less emitting alternatives for our land use.”
NZ could potentially find some middle ground in that spectrum, tempering pastoral land use while also developing mitigation tools for livestock emissions.
“Finding such a middle ground will take time.
“For now the reality check from our study is livestock is not an artefact of an accounting policy introduced by the UN Climate Change Convention. Its contribution to climate change is real.
“The research shows it is essential to reduce livestock emissions in order to reduce climate change consistent with the Paris Agreement, otherwise the task becomes even more difficult than it is already.”
