The atmospheric concentrations of CH₄ observed this autumn/winter represent a maximum in the series of measurements available to date. These maximum values have been observed both from space platforms, thus affecting the entire atmospheric column, and at surface level, as is the case of the Izaña Global Atmospheric Watch station (Agencia Estatal de Meteorología), which belongs to the observation programme of the World Meteorological Organisation.

At the Izaña Observatory, the monthly averages of CH₄ surface concentrations recorded during October (1940 ppm), November (1959 ppm) and December 2021 (1952 ppm) are the highest ever since the greenhouse gas observation programme began in 1984.

It is too early to assess the causes of these increases, but studies are currently focused on analysing possible anomalies in the balance between emissions from biological sources and fossil fuels, and their chemical destruction in the atmosphere. However, some preliminary work suggests that anomalous warming of the westernmost part of Siberia and its sea ice may be releasing anomalous CH4 emissions into the atmosphere associated with the melting of permafrost in these areas.

 The climatic effect of these anomalous CH₄ emissions will depend on their duration, i.e., whether they are one-off emissions or a significant and permanent change in observed trends. In the latter case, they may contribute to the observed warming, especially in the medium term.

This is the largest measured annual increase since 2011 and is highly significant considering that the past two years have seen an economic (and in principle anthropogenic emissions) slowdown caused by the response to the coronavirus pandemic. Despite this slowdown, methane levels continue to rise relentlessly.

CH₄ remains in the atmosphere for a shorter period of time than CO₂ (about 10-12 years) and is considered a short-term climate forcer. Although its emissions are lower than CO₂, its global warming potential (ability to trap heat in the atmosphere) is 28-34 times higher. The observed annual increase in methane concentrations is therefore a very negative impact on the fight against climate change.

At this stage, it is very difficult to give a precise explanation as to why this peak is occurring. Specific studies will be needed to analyse different factors affecting global methane concentrations in the atmosphere, such as changes in the different emission sources (biological and anthropogenic) and potential variations in the chemical processes responsible for removing methane from the atmosphere. The causes are likely to be a combination of all these elements.

As an illustration, the European Space Agency (ESA) recently published a news item suggesting that during 2020 and in a large oil and natural gas production area in the USA, CH₄ emissions had increased compared to the previous year. One possible explanation for this could be that, as a result of lower demand for natural gas in the industrial sector due to covid-19, natural gas is burnt, leading to higher methane emissions in this area. I repeat that this example is only illustrative and does not pretend to explain the causes of the observed peak, but there are surely multiple reasons that will have to be analysed during the following months.
 

In numbers, this record methane emission is important because methane has increased by about a factor of 2.5 since pre-industrial levels. Its concentration stabilised during the first half of the 2000s and has continued to grow since then (about 63 ppb in the period 2011-2019). In the last three years its growth has accelerated despite the pandemic.

In terms of environmental impact, it is important because the increase in methane leads to increases in tropospheric O3, which is relevant for pollution and health, and in stratospheric water vapour, which also influences the radiative balance.

Methane emissions contribute to global warming. The contribution of methane to the atmosphere is smaller than that of CO₂, but its relative effect per unit is larger (one tonne of methane is equivalent to almost 30 tonnes of CO₂ in its radiative effect). It has no immediate short-term implications but is relevant to the achievement of net zero emissions targets by the middle of this century.

Rising CH₄ levels contribute to global warming and must be taken into account in emission reduction strategies. It does not facilitate them because part of methane emissions are of natural, not anthropogenic, origin.

The causes of this recent acceleration in concentrations are undoubtedly due to an increase in emissions. The specific origins of these emissions are under study. However, several natural and anthropogenic factors contribute. Temperatures in the Arctic and precipitation in the tropics contribute to inter-annual variations with emissions from wetland areas where decomposing material is present. The most likely causes of growth in the last decade are agriculture and livestock, which have seen increases in emissions in the last decade, as well as oil and natural gas production, including losses from leaking pipelines in the transport of oil and natural gas.