‘WAKE UP NZ’
Says climate-change scientist
Livestock are responsible for almost a quarter of all global warming – which is more than estimates based only on greenhouse gas emissions – and 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.
‘‘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, a short-lived gas which remains in the atmosphere for 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, 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.’’
Reisinger said he hoped the findings helped answer any lingering questions over the role that livestock emissions have on climate change.