A few months back I tried to get to the bottom of the wide range of statements about the steel sector’s CO₂ emissions. The answer was that the production of crude steel is responsible for emitting around 3.7 Gt of CO₂ – 8% to 10% of human emissions (see: ‘6%, 7%, 8%, 9%, 10%, 11%…’).

But that is for CO₂ only. What about other greenhouse gases, and in particular, what about methane?

I thought this would be a case of looking up the information and summarising it.  If only it were so simple.

The World Steel Association, worldsteel, is completely silent.  In fact, it is silent twice: firstly because it reports the sector’s emissions on a ‘CO₂ only’ basis; and secondly because it doesn’t count the upstream emissions associated with the sector’s use of mined materials, where the vast majority of its methane emissions occur.

First, some background. Then some numbers.

Methane is a colourless, odourless gas made up of carbon and hydrogen: four atoms of hydrogen to one of carbon – hence CH₄. It is generated naturally when microorganisms decompose organic matter in the absence of oxygen, in wetlands, and in the digestive systems of many herbivores – notably those of cows and sheep, as well as in the guts of termites (termites may be small, but there are lots of them!). It can also be produced when organic matter is incompletely burnt.  And vast quantities of ‘fossil methane’ accumulated over hundreds of millions of years through the compression and heating of dead vegetation in the geological processes that produced oil, coal, and natural gas.

Methane is broken down naturally by chemical and biological processes in the presence of oxygen in the atmosphere and soil, eventually to carbon dioxide (CO₂) and water (H₂O). 

Prior to industrialisation the natural cycle of methane generation and breakdown was more or less in balance, with around 0.7 parts per million (ppm) of methane circulating in the earth’s atmosphere, and the fossil methane trapped beneath impervious layers of rock and salt.

That all changed as the human population grew from less than one billion in the 19^th century to more than 8 billion today, and as the exploitation of coal, oil and natural gas allowed fossil methane to escape into the atmosphere.

Today, around 351 million tonnes (Mt) of methane are released into the atmosphere each year from agriculture (especially wet rice cultivation), from landfill sites and sewage farms, and from the extraction, processing and transportation of fossil fuels, in addition to 233 Mt from natural processes.

Figure 1. Data from:  https://www.iea.org/data-and-statistics/charts/sources-of-methane-emissions-2023-2

Natural and anthropogenic emissions together now overwhelm the capacity of natural systems to break methane down, and the concentration in the atmosphere has increased from 0.7 ppm to around 1.9 ppm – getting on for three times as high as the pre-industrial level.

1.9 parts per million doesn’t sound like much. The atmospheric concentration of CO₂ is now going on for 420 ppm – more than 200 times as high.  And human emissions of CO₂ amount to around 43 billion tonnes a year – 100 times more than methane.

The problem is that quantity-for-quantity, methane is about 120 times more effective than CO₂ at trapping energy in the earth’s atmosphere, and in consequence much more effective at heating the planet.

We’ll come back to this in more detail later but for now let’s just ask, ‘should we be worried’?

And the short answer is yes, very much so.

The average global temperature today is about 1.4 degrees higher than it was prior to industrialisation.  And around one third of that temperature increase is due to methane emissions rather than CO₂ emissions. So methane is a big deal.

And what has that got to do with steel?  After all, steel emissions do not feature in the pie charts in Figure 1.

But look a bit more carefully.  3% of global methane emissions are from the production of coking coal – almost all of which is used for the production of iron and other metals use for steel making. According to the civil society organisation EMBER, methane emissions from the extraction of coking coal add the equivalent of 27% to the steel industry’s CO₂ emissions ‘on a 20 year climate impact basis’¹.

But 8% of steel is made from Direct Reduced Iron (DRI), produced using natural gas (methane) as fuel – a figure that is expected to increase dramatically in the coming decades.  Steel is also made using charcoal – whose production generates methane.  And steel made from recycled scrap uses huge quantities of electricity, much of which is generated today using ‘thermal’ coal and natural gas.

So steelmaking is clearly responsible for the emission of a lot of methane, and not only from its consumption of coking coal.  But how much?  And what is the impact of those emissions on the world’s climate?

The following posts are my attempt to find out. First up, ‘Steel’s methane footprint’…

References

1. see ‘Why the steel industry needs to tackle coal mine methane’ ↩︎