Livestock are responsible for almost a quarter of all global warming, says Dr Harry Clark, director of the New Zealand Agricultural Greenhouse Gas Research Centre.

Livestock are responsible for almost a quarter of all global warming, which is more than estimates based only on greenhouse gas emissions.

Climate change scientists say this a wake up call for New Zealand.

About half of the country's greenhouse gases come from stock, but a new calculation for global warming includes methane emissions.

Livestock were calculated to contribute about 23 per cent to global warming, by New Zealand Agricultural Greenhouse Gas Research Centre deputy director Dr Andy Reisinger​ and director Dr Harry Clark. They have just published a paper about how much livestock emissions contributed to global warming, in the scientific journal Global Change Biology.

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"It is important for farmers and New Zealand to think about the impact of stock on global warming. It is not something to be ignored, and if we want to hold global warming to 1.5 or 2 degrees Centigrade, we will have to include livestock," said Clark.

The new estimate took into account methane, which is a short lived gas in the atmosphere of 12 years. Carbon dioxide (CO2) has a 1000 year decay period, and nitrous oxide (NO3) about 100 years.

Clark said global warming calculations were done in 100 year blocks, and while CO2 and NO3 estimates were about right, methane's impact on global warming needed to be factored in.

He said the revised figure was much greater than common estimates for global greenhouse gas emissions, and demonstrated that methane played a critical role in global warming.

Clark said many farmers thought that because methane was a short lived gas emitted from stock, it had little impact on global warming.

Reisinger said some people argued that comparing emissions using the so-called Global Warming Potential was wrong and that efforts to reduce methane were misplaced because it was a short lived greenhouse gas.

"So we used a simple climate model to understand how much the emissions directly attributable to livestock contribute to actual warming," he said.

"We found that of the warming the world had experienced by 2010, as much as 19 per cent was due to direct historical methane and nitrous oxide emissions from livestock. Once you add the warming due to emissions when land is converted into pastures, you end up with a total contribution of 23 per cent to current warming."

He said the estimate did not consider indirect emissions from energy use or growing livestock feed such as soy beans, so this could be taken as "a lower bound" of the actual contribution of livestock to current warming.

Reisinger said their study also looked at how much livestock would contribute to future warming.

"If emissions from all sectors were to increase unabated, the world would warm by more than 4C but livestock would make a declining contribution to this. In other words, if the world goes to hell in a hand-basket, it won't be because of livestock," he said.

"But if the world makes efforts consistent with the Paris Agreement to rapidly reduce emissions from all sectors, including livestock, then livestock could still contribute almost one fifth of the warming in 2100. That's a big part and shows that reducing livestock emissions can play an important role in helping achieve the goals of the Paris Agreement."

The study also looked at how reductions in livestock emissions would impact on allowable carbon dioxide emissions consistent with long term temperature goals.

"We know that net global carbon dioxide emissions have to go to zero sometime after 2050 to limit warming to 1.5-2C. This fact doesn't change regardless of what we do with livestock emissions.

"But if we could reduce livestock emissions beyond what is currently considered feasible, this would give us just a little more breathing space in that herculean effort to phase out carbon dioxide completely."

Reisinger said he hoped the findings helped answer any lingering questions over the role of livestock emissions have on climate change.