Methane – a greenhouse gas

Methane comprises just 0.00018% of the Earth’s atmosphere – so why are we concerned about it?

Methane (CH₄) is a greenhouse gas. It is the second-most abundant greenhouse gas after carbon dioxide (CO₂). Although methane is emitted in smaller quantities than carbon dioxide, its global warming potential is around 25 times that of CO₂. This means that it is more effective in trapping heat. Fortunately, methane has a short lifespan – emissions only last for about 10–12 years in the atmosphere. Making methane reductions now will have a significant impact in our lifetimes.

So many aspects of climate change are happening faster than expected. We see more fires, more of the strongest hurricanes, more heatwaves, and methane is the best lever we have to reduce the growth in those over the next 30 years.

Professor Drew Shindell, Duke University

Natural sources of methane

Wetlands are the largest natural source of atmospheric methane. Microorganisms living in water-logged soils produce methane, and some of this makes its way into the atmosphere. Other sources include decaying organic matter on the ocean floor and lake beds, wildfires and even termites. Believe it or not, termites around the globe generate up to 20 million tonnes of methane per year! It is produced while digesting cellulose. Compare this to human digestion – we produce less than 0.5 million tonnes of methane in our burps and farts annually.

Even though these sources are natural, human activity influences natural emissions. Research shows that hydro dams and reservoirs produce nearly as much methane as landfills. Climate change is leading to more wildfires and accelerating methane releases from the Arctic seas and soils as permafrost warms and ice melts.

While wetlands and oceans are sources of atmospheric methane, they are beneficial since they have crucial roles as carbon sinks – removing and storing atmospheric carbon dioxide.

Human-caused methane emissions

Methane that is produced as the result of human activities is known as anthropogenic emissions. The United Nations Environment Programme reports that more than half of these global methane emissions come from three sectors:

• Fossil fuels – 35% of emissions come from oil and gas extraction and processing and coal mining.
• Waste – 20% of emissions come from landfills and wastewater.
• Agriculture – 40% of emissions come from livestock and rice cultivation.

Aotearoa New Zealand’s methane emissions

Aotearoa New Zealand’s methane emissions profile is different from the global profile. Around 85% of our methane emissions come from agriculture and dairy. We have lots of ruminants – sheep, cattle, deer and goats – that burp out methane as they digest their food.

The second-largest source of methane in Aotearoa is waste. Methane forms in landfills as microorganisms break down organic matter like food or paper. Methane is also produced during wastewater treatment. Microorganisms are used to digest (break down) solid waste to make the wastes safer to handle and remove the odours. Modern landfills and wastewater treatment plants are designed to capture methane and use it to generate electricity. Older landfills and treatment plants are not as efficient at capturing methane.

Additional methane emissions come from natural gas leaks when we take fossil fuels out of the ground. Methane leaks from oil and natural gas wells and from coal mines. Leaks also occur during gas production and in transmission pipelines.

Reducing our methane emissions

Aotearoa has set national and international targets for greenhouse gas reductions. To reach these targets, we need to reduce our methane emissions. Scientists with the New Zealand Agricultural Greenhouse Gas Research Centre and industry groups are researching on-farm actions and technologies to reduce emissions. Some of these actions are available for immediate use, while other developments are still under investigation.

Outside of the agriculture sector, the energy and waste industries are working to fix leaks and upgrade networks. We can all do our part by reducing what we send to landfills – composting organic materials instead of burying them is a good place to start.

Finding methane sources

In order to deal with methane emissions, we need to know where the gas is coming from. There are several ways that scientists can monitor emissions from the land, but new technologies using satellites enables scientists to work at much larger scales.

MethaneSAT is the world’s first satellite dedicated solely to tracking methane emissions. Its sensors can accurately measure methane concentrations and emission rates and track the emissions back to their origins. The data it produces is publicly available, free of charge.

MethaneSAT is Aotearoa New Zealand’s first government-funded space mission. Engineers operate the satellite’s mission control, while atmospheric scientists and modellers oversee the agricultural methane detection programme.