Causes: Methane CH4
Dairy cows are our single largest source – image Monika Kubala | Drilliing for gas – image J. Penrose
Summary
Methane (CH4) is created though biological process. Liquified natual gas (LNG) is mostly methane, not a climate-friendly alternative or low-emissions transition energy. This map shows the incredible volume being leaked into the atmosphere far faster than climate models anticipated.
The atmospheric methane growth rates of the 2020s far exceed the latest baseline projections. – Shindell et al 2024
During the first 20 years after methane is emitted into the atmosphere, it was previously assumed to have 84 x the global warming potential of CO2. Around 50% of warming happens within 12.4 years, after which some breaks down into carbon dioxide CO2, adding to existing warming potential. This assumption was based how quickly hydroxyl radicals (OH) in the troposphere break down the methane. However:
Current models uniformly underestimate the atmospheric lifetime of methane because they uniformly overestimate how much hydroxyl radical (OH), the chemical species responsible for most of the destruction of methane, the atmosphere contains. – Science 2024
The amount of methane in the atmosphere is 250% higher than above pre-industrial levels and increasing (Fig. 1) mostly due to agriculture and the natural-gas industry. This acceleration is in part due to political decisions, and increasing warming leading to a feedback effect that’s accelerating melting vast areas of permafrost and some wetlands. Paradoxically, it’s also in part due to the reduction of pollution in emissions that help break down methane. Research published February 2020 revealed a way to distinguish emission from biogenic sources—agriculture, livestock etc—and fossil fuel sources.
Methane from agriculture accounts for 53% of New Zealand’s greenhouse gases—our largest single contribution by sector. As a result, Aotearoa has the largest methane emission rate per person/year (0.6t) in the world—six times the global average.
Under the NZ Emissions Trading Scheme and Climate Change Response (Zero Carbon) Act, the National/ACT/NZ First coalition government gave agriculture a free pass, ignoring the economic benefits of reduction and the catastrophic implications for the economy:
The global monetized benefits for all market and non-market impacts are approximately US$4,300 per tonne of methane reduced. When accounting for these benefits nearly 85% of the targeted measures have benefits that outweigh the net costs. The benefits of the annually avoided premature deaths alone from a 1.5°C-consistent-methane mitigation strategy is approximately US$450 billion per year. – UN Global Methane Assessment 2021
Contrary to popular claims, growing grass does not offset agricultural emissions:
Grassland carbon stocks would need to increase by approximately 25−2,000%, indicating that solely relying on carbon sequestration in grasslands to offset warming effect of emissions from current ruminant systems is not feasible. – Wang et al 2023
What’s covered on this page:
Methane: where does it come from?
Methane is produced by single-celled ‘methanogenic’ microorganisms that feed on plants in anaerobic (oxygen-free) conditions. They are vital microorganisms because the help decay dead plants and animals. This helps to recycle the nutrients back into the food chain. In the same way that we and other animals breath out carbon dioxide as a waste product, these organisms release methane is a waste product. Methanogenic microorganisms are some of the oldest forms of life on Earth (Archaea) and they’re found everywhere, including in some trees.
Most of the methane these organisms produce is absorbed back into the ground. Much was locked away for many millions of years along with coal (which is why it’s so often found in coal mines) and during the most recent Glacial epoch as frozen clathrates. However, clathrates are now defrosting (see the tab below) the microbes have sprung back into life, and methane is escaping into the atmosphere at a rapidly accelerating rate.
The New Zealand Greenhouse Gas Inventory 2024 report summarised in the graph below uses a range of parameters to assess how much methane is produced by different activities. Some of this is based on estimates, others on actual measurements. Agriculture produces 53%.
Agriculture: ruminant animals (cows, sheep)
These are the largest producers of anthropogenic methane gas in Aotearoa (Fig. 2). The following figures come from Greenhouse gas emissions on New Zealand farms: A companion guide to the climate change seminar series for rural professionals July 2022
Methanogenic microorganisms live in the gut of these animals to breakdown the food using a process called enteric fermentation (Fig. 3).
- A sheep can produce ~30 litres of methane/day
- A beef cow can produce up to 232 litres/ per day
- A dairy cow can produce up to 375 litres/day. In 2024/25 there were ~4.68 million dairy cows in Aotearoa. This has not substantially changed since 2023/2204 (Fig. 4)
These emissions are EXEMPT from the New Zealand Emissions Trading Scheme.
Burning the Amazon for fast food chains
While enteric fermentation is natural in grazing animals, around the world, particularly in places like Brazil, humans have burned down millions of hectares of forest and wetlands that once recycled methane efficiently, with millions of domesticated ruminants that graze on grass or are fed grains from grasses.
Agriculture: effluent & fertilisers
Effluent pondsResults from our investigation indicate that the national GHG Inventory is currently underestimating dairy effluent pond CH4 emissions by a factor of 1.7 to 4. Ministry for Primary Industries (MPI) noted that: ‘Currently there is widespread interest in removing animals from pastures and placing them on stand-off pads or more permanent housing.’ If this shift in animal management occurs, it would have an enormous impact on the way that dairy effluent is managed. The time that cows spend on sealed surfaces would increase, so that more manure would need to be treated by effluent ponds, resulting in higher CH4 emissions. If a much higher proportion of the total daily dairy cow waste production is collected, and manure management practices are not changed, manure CH4 emissions have the potential to equal the current main agricultural GHG sources of enteric methane and pasture nitrous oxide emissions. – MPI report
Agriculture: growing rice
While very little rice is grown in New Zealand, globally ~3.5 billion people depend on rice for more than 20% of their daily calories and ~1 billion depend on it for their income. The conditions in which rice is grown are ideal for bacteria and methanogens to produce methane and nitrous oxide (a greenhouse gas 298 times more potent than CO2). Perversely, techniques intended to reduce emissions while also cutting water use, may be increasing emissions, meaning methane from rice cultivation may be up to twice as bad as previously estimated.
Agriculture, particularly vast areas being converted to rice growing, is one of the reasons cited for why greenhouse gases gradually began increasing in the atmosphere thousands of years ago, long before fossil fuels started to be burned to produce energy.
Rice is is such demand globally that in many Asian and South East Asian countries like the Philippines where this photo was taken, entire hills and mountains have been re-sculptured over centuries, possibly millennia in some places, to grow rice on terraces. Background Image: Wikipedia CC license.
Landfills
The left side of the list below shows the top 25 highest methane emissions from landfills. Under Open the Data click any Data link to open a world map where you can zoom in to Aotearoa.
The data show more than 2,994 plumes from 707 waste sites, including landfills and dumpsites, worldwide. These are sites in dozens of countries of all income levels and in all world regions. While many landfills emit only a few dozen kilograms of methane per hour, those on our “top 25” list emitted much more – ranging from 3.6 to about 7.5 tonnes (metric tons) of methane per hour.
In this iteration of our top 25 list, we are including a column titled “potentially responsible operator.” This information was not obtained directly from Carbon Mapper. Instead, the information is the result of research conducted by our team at the Emmett Institute. Below, we explain the methodology for that research and welcome feedback. – UCLA Law 20 April 2026
Industry | burning coal, oil & gas | fugitive emissions
Burning coal and oil releases methane. Recently, New Zealand scientists, amongst others, have determined that burning fossil fuels is adding 35-40% more methane into the atmosphere than previously thought (ie, it is is not yet included in current inventory calculations). In addition to this, burning methane releases CO2 in the atmosphere.
Industry: A small amount of methane is produced during these processes, including cement and methanex manufacturing.
Fugitive emissions happen because methane is less dense than air, so it’s lighter, which means it can easily escape into the atmosphere during mining, transport, manufacturing, and storage—including escaping from the gas bottles used for BBQs. As it’s highly flammable, any gas that builds up too much pressure must be vented, ie leaked into the atmosphere. Some but not all mines burn some of this excess gas in a process called ‘flaring’.
This does not include the 485,000 tonnes of methane that escaped to the atmosphere when the Nord Stream pipeline was sabotaged.
In 2026 the UCLA Stop Methane analysis is based on data from Carbon Mapper and found 4,400 significant plumes in 2025, each emitting more than about 100kg/hour. That’s 3.8 billion tonnes of methane emitted just from ‘significant plumes’, that is, fugitive emissions. See also Landfill above.
Melting permafrost and burning lakes
Permafrost is a combination of soil, sediment, and the remains of dead plants and animals that stay at or below 0°C for at least two years. Unlike ice, it doesn’t ‘melt’ once temperatures rise above 0°C. Permafrost falls apart, and the organic material decomposes, just as frozen meat or vegetables left outside a freezer will decompose if not eaten. When this decomposition happens an environment where there’s oxygen, such as outside your fridge on the sink, carbon dioxide is released. If the environment is anaerobic (lacks oxygen), such as underwater in lakes, wetlands, and the ocean, methane is released (Video 3).
Permafrost can be as thin as <1m and as thick as >1,000m. It covers approximately 22.79 million km² (about 24% of the exposed land surface) of the Northern Hemisphere.
Melting permafrost is the result of a feedback effect of climate change, that is anthropogenic forcing is a triggering natural forcing.
In 2019, NOAA estimated that melting permafrost was contributing 600 million metric tonnes of net carbon (methane and carbon dioxide) per year into Earth’s atmosphere.
By 2100, near-surface permafrost area could release 10s to 100s of gigatonnes of carbon as CO2 and methane to the atmosphere. – IPCC, 2019
Melting clathrates & burning ice
Background photo: Katie Orlinksy, National Geographic
