Methane

 What About Methane Especially from Agriculture?

Abstract

Methane is nothing like as potent a greenhouse gas problem as carbon dioxide and the majority is being emitted by fossil fuel extraction and consumption, and so will be controlled when carbon extraction is controlled. Agricultural methane is an increasing but minor player. But methane's impact is being underrepresented by using its half-life to spread its greenhouse warming potential over 20 or 100 years.

A growing problem

There has been a lot of discussion in the press and on social media about the amount of methane emitted from agriculture, especially from cattle. Maybe we all need to change to a vegan diet to stop climate change?

The latest IPCC report AR6 shows that methane is a significant factor, so large a factor that I was shocked.

Detail from Assessed contributions to observed warming in 2010–2019 relative to 1850–1900

This is the full diagram from IPCC AR6 - Climate Change 2021 - The Physical Science Basis - Summary for Policymakers

Figure SPM.2: Assessed contributions to observed warming in 2010–2019 relative to 1850–1900.

Note that the AR6 Press Conference did not drill down to the detail of CO₂ and methane, but only displayed the left half of the above diagram.

AR6 Press Conference Slide

When I looked at the data it didn't seem that methane emissions had changed that much over the last few decades since 1990.

 

Note: The source data methane (CH₄) emissions are measured in tonnes of carbon dioxide equivalents (CO₂e) based on a 100-year global warming potential value but displayed as (GtCO₂e) to match graphs on other pages in this blog.

I next looked at how methane emissions have changed in the above graph since 1990 to find out where the threats to climate from methane sources are.

Clearly fugitive emissions are increasing most. Note that fugitive emissions are the methane that escapes during the process of drilling, extracting and transporting natural gas. Combined with 'Other Fuel Combustion' this increase is more than twice as large as that from Agriculture.

So how does methane compare with carbon dioxide in importance - the data doesn't make sense. I was expecting methane to be less than carbon dioxide, but this shows methane emissions as only about 1% of CO₂. I thought that CO₂ equivalence (CO₂e) made them comparable, and the IPCC radiative forcing diagram at the top of this page would put their effects in the same order of magnitude.

Crosschecking from other sources (this is from globalmethane.org) even when methane emissions are sliced in a different way, fossil fuels are still by way the most significant, both in size and rate of increase.

Returning to the data on measured concentrations of methane and carbon dioxide over time shows how carbon dioxide is by far the most significate gas, both because of it's abundance and rapid increase.

Another important comparison is between methane changes actually measured in the atmosphere and estimated methane emissions. 

Clearly most of the emitted methane is being either sequestered or converted to carbon dioxide.

Radiative Forcing

This is the difference between 1750 and now. So the measure of what humans and the industrial revolution have made happen.

Every year the NOAA issue the graph above. The data can also be shown as below.

I think this shows more clearly that methane is less of a problem than CO₂.