The island nation, dubbed the Saudi Arabia of milk for its dominant role in global dairy trade, faces a reckoning over how to balance the outsize contribution that ranchers make to the economy against New Zealand’s need to meet its greenhouse gas pledges. Last year, New Zealand — which has pledged to reach net-zero carbon dioxide emissions by 2050 — proposed a first-in-the-world tax on cow emissions. The levy will depend on factors including the number of animals kept, the size of the farm, the type of fertilizer used and steps farmers take to reduce their emissions. It’s expected to reduce the amount of methane New Zealand’s livestock release into the atmosphere by as much as 47 percent by 2050. Some farmers will need to reduce their herds to meet those targets, which many worry could drive them out of business. Government modeling suggests that by 2030, sheep and beef revenue would drop by around 20 percent — making many  farms nonviable. The clash between the agriculture industry and government efforts to reduce emissions is playing out around the world. About a third of all human-caused global greenhouse gas emissions are linked to food. The largest share comes from agriculture and land use — including methane emitted by the planet’s 1.5 billion cows and other livestock, nitrous oxide from fertilizers and carbon dioxide from clearing forests for farmland. The U.N. Intergovernmental Panel on Climate Change notes that one way to reduce food emission is to stop consuming so many animal products — a shift that New Zealand and other nations reliant on animal-based exports hope to avoid. Former Prime minister, Jacinda Ardern argued the tax would help New Zealand become carbon neutral and preserve the clean, green image of its farm products among global consumers. The day of Ardern’s announcement, the nation’s biggest dairy export cooperative, Fonterra, announced it was partnering with Nestlé in a bid to develop a commercially viable dairy farm with net-zero carbon emissions.