Natural gas: what does it mean for the climate?

Natural gas is often presented as a transitional energy for electricity production, with CO2 emissions well below those of coal. The term 'natural' also has a positive connotation for what remains a fossil fuel on which we are very dependent. Let's take a moment to decipher.

The sharp rise in energy prices in recent months has put "natural gas" back in the spotlight and reminded us how dependent we are on fossil fuels. While coal represented only 2% of primary energy in 1800, its share peaked at 55% in 1910, and was still 25% in 2019. Coal, oil and gas still constituted more than 80% of our energy in 2020. The latter is the most recently deployed fossil fuel, accounting for only 5% of energy consumption after 1945, and is often presented as a 'transition' fuel.

First of all, it is interesting to clarify why the word 'natural' is almost systematically attached to the word gas. After all, we are not talking about natural oil. In 1792, a Scottish inventor, William Murdoch, developed a system for lighting his home with coal gas - formed from coal. This gas is produced for example during the manufacture of coke, a porous solid with a very high carbon content formed by heating coal to 1100 degrees in the absence of oxygen, which is used for the manufacture of steel. The ownership of the discovery of the properties of this gas remains uncertain. It enabled the significant development of artificial lighting. At the beginning of the 19th century, Paris and London installed coal gas lamps and a distribution network to illuminate their streets. However, at the end of the 19th century, gas was dethroned by electricity for lighting. It remained in use until the 1950s for domestic purposes, under the name of town gas.

The name "natural gas" was therefore used to distinguish it from coal gas. It is mainly composed of methane (CH4), between 85 and 95%, and of other volatile carbon compounds (ethane, propane, butane, etc.). Per unit of mass, it is the fossil fuel with the highest energy density: 55 MJ/kg against 42-47 MJ/kg for oil. However, as its name indicates, it is gaseous at ambient temperature and pressure, and therefore has a low energy density per unit volume. This means that it must be compressed or even liquefied for certain applications. It becomes liquid at a temperature of -161 ºC.

The term 'natural' is not insignificant. A study published in 2021, and carried out in the United States, studied the reaction to different synonymous names for gas ("natural", "methane", "fossil", "shale"). The term "natural gas" was perceived positively, while methane was perceived very negatively. The term natural was associated with "clean" while methane was associated with "pollution". Interestingly, reactions to the terms "fossil" and "shale" were strongly dependent on political orientation - Republican participants were more positive towards these terms. Given these results, the fact that gas is a highly CO2 emitting fossil fuel, and that coal gas is no longer used, the word natural should no longer be used to describe it.

This is particularly important as gas plays an important role in the decarbonization of energy, hence its qualification as a transition fuel. Although its combustion emits CO2, it emits 2 times less per kWh produced than coal, and nearly 3 times less for a combined cycle power plant. Thus, the replacement of many coal-fired power plants by gas-fired plants in the USA between 2005 and 2018, mainly motivated by the very low price of gas, has reduced CO2 emissions from electricity production by 27%. Over this period, the share of coal in electricity was divided by 2.6 while the share of gas doubled.

But methane is itself a gas with a very powerful greenhouse effect. Its warming power is about 30 times greater for a period of 100 years, and 85 times greater for a period of 20 years - methane progressively degrades in the atmosphere. Releasing methane into the atmosphere is therefore much worse in the short and medium term than CO2. So-called fugitive emissions are defined as emissions produced unintentionally and include leaks from industrial facilities and pipelines. In 2015, they represented the equivalent of 2.3% of US gas production, greatly diminishing the interest of switching to gas from a climate point of view. However, these emissions can be greatly reduced by at least 40% at no additional cost. During the COP26, more than 100 countries committed to reduce their methane emissions by 30% by 2030.

About 40% of the gas imported into Europe comes from Russia, far ahead of Norway (18.5%) and Algeria (11.3%). Consumption increased by 35% between 1990 and 2018. About 20% of the electricity in Europe is produced in gas-fired power plants. These have very interesting qualities for electricity production. They can start up in a few minutes and are able to vary their power very quickly, which makes them ideal complements for variable energy sources such as solar and wind, while waiting for the development of biogas and storage facilities on a larger scale. This high flexibility means that gas-fired power plants in Europe are often used to maintain the balance of the electricity grid. As the price of electricity on the markets is determined by the marginal means of production, the recent sharp rise in the price of gas has had a strong impact on electricity prices in Europe.

If the replacement of coal by fossil gas has an interest in lowering emissions, subject to the control of fugitive emissions, its use can only be limited in time. As recently reminded, nearly 60% of the gas reserves must remain unused to stay under the 1.5 degrees of warming...

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