Beyond CO2: methane, nitrous oxide and the hidden climate crisis

Around 40 per cent of methane comes from natural sources, notably wetlands. The other 60 per cent is linked to human activities such as agriculture, including ruminant breeding and rice cultivation, fossil fuels, and waste.

Its warming power is more than 80 times greater over 20 years than that of CO2, but its lifespan is shorter, making it an important lever in attempts to limit global warming in the short term (see graphic).

Reducing methane emissions “would have a strong short-term cooling effect because atmospheric methane concentrations would drop quickly,” said Mathijs Harmsen, a Netherlands Environmental Assessment Agency PBL researcher.

Policies should “focus on capturing the low-hanging fruit – the very low-cost measures such as reducing natural gas leaks,” he said.

Despite a global commitment to reduce planet-heating emissions signed by many countries, including the European Union and the United States, the outlook is not positive.

“Methane is rising faster in relative terms than any major greenhouse gas and is now 2.6-fold higher than in pre-industrial times,” said an international group of researchers under the Global Carbon Project in a study published in the academic journal Environmental Research Letters.

Nitrous oxide, or nitrous protoxide (N2O), is the third major greenhouse gas, almost 300 times more potent than CO2. It is mainly emitted by synthetic nitrogen fertilisers and manure used in agriculture.

Other emissions come from human activities like the chemical industry, waste water and fossil fuels, or natural sources such as the soil and oceans.

Study shows Greenland absorbs more greenhouse gas methane than it emits

“Global human-induced emissions, which are dominated by nitrogen additions to croplands, increased by 30 per cent over the past four decades,” concluded a major study in the journal Nature in 2020.

The key to the problem lies in the more efficient use of fertilisers.

“Two-thirds of the climate change mitigation potential of N2O could be realised by reducing fertilisers on just 20 per cent of the world’s cropland, particularly in humid subtropical agricultural regions,” wrote French researcher Philippe Ciais in 2021.

Fluorinated greenhouse gases (PFCs, HFCs and SF6) are found in fridges, freezers, heat pumps, air conditioners, and electrical networks. Even in small quantities, they stand out for their extremely high warming capacity.

For example, SF6, found in electrical transformers, has a greenhouse effect 24,000 times greater than CO2 over a 100-year period.

The Montreal Protocol, signed in 1987 and ratified by 195 countries, has significantly reduced the atmospheric presence of CFCs, another ozone-depleting fluorinated gas. In 2016, the Kigali agreement also provided for the phasing out of HFCs.

Last year, the EU sealed a pact to progressively ban the sale of equipment containing fluorinated gases, particularly HFCs, to eliminate them completely by 2050.

What are HFCs and what are the alternatives?

HFCs are a type of coolant. They were introduced as a replacement for chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), which were harmful to the ozone layer.

While HFCs do not directly deplete the ozone layer, they contribute significantly to global warming.

Some alternatives include ammonia and hydrocarbons such as propane and butane.

However, there are some concerns because they are flammable and need to be handled carefully and with proper safety measures in place.

Scientists are still looking for a better, safer, and environmentally friendly option.