Which is the bigger contributor to climate warming, cows or cars? To answer this question, it’s helpful to unbundle greenhouse gases into their main constituents and recap how we (should) compare them.

Greenhouse gases are so called because they let incoming sunlight pass through but then trap heat radiated back from the planet’s surface. The most important one, and the largest contributor to the Earth’s greenhouse effect, is (perhaps surprisingly) water vapour. It probably accounts for about 60 percent of the warming effect. However, unlike other greenhouse gases, water vapour does not control the Earth’s temperature but instead is controlled by the temperature. For example, when the temperature drops, water vapour condenses into droplets that make up clouds.

Other greenhouse gases do not condense in the same way as water vapour and so the atmosphere can hold much more of them. There is a whole family of these non-condensable greenhouse gases, and they are not all created equally. Some are much better than others at retaining heat. Some are short-lived while others can last decades in the atmosphere. Some are emitted in vast quantities but are inefficient at trapping heat whereas others are emitted in only trace amounts but are extremely efficient. The principal greenhouse gases in this family are carbon dioxide, methane, nitrous oxide and fluorinated gases.

Carbon dioxide is the primary greenhouse gas emitted through human activities. For that reason, when making comparisons, scientists convert other greenhouse gases into the equivalent amount of carbon dioxide with the same warming potential. Since greenhouse gas emissions are often calculated in terms of carbon dioxide equivalents (CO₂e), they are often referred to simply as “carbon emissions”.

Methane is another principal greenhouse gas, emitted from oil and gas production and transportation; from livestock and other agricultural practices; and from the decay of organic waste in landfill sites. Methane is so pernicious because it has more than 80 times the warming potential of carbon dioxide over its first 20 years in the atmosphere. Even though carbon dioxide has a longer-lasting effect, it’s methane that sets the pace for warming in the near term.

So, back to our question of which are worse – cows or cars?

According to the UN Food and Agriculture Organisation, livestock on EU farms (including the UK) in 2018 were responsible for emitting around 502 million tonnes of carbon dioxide equivalent a year, mostly through the methane they release. When the greenhouse gas emissions associated with growing their animal feed are also taken into account, the total annual carbon emissions are 704 million tonnes. This figure compares with 656 million tonnes of carbon dioxide from all of Europe’s cars and vans in the same year.

Speaking in terms of carbon emissions – in other words, in carbon dioxide equivalents – enables us to compare the differing contributions of greenhouse gases to climate warming in an understandable way. We can do away with the complexity of a carbon footprint that consists of lots of different greenhouse gases by expressing it as a single number and focus instead on reducing that number. When we look at this number for cows and for cars, we see clearly that the question is no longer which one is worse. The real question is how do we reduce the significant carbon emissions of both?

— source+©: https://carboncopy.eco/blog/are-cows-worse-than-cars

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There’s an elephant in the room and it’s the greenhouse gas emissions from goods we consume in the UK that have been imported. They don’t count because we choose not to count them.

Most countries generally use ‘production-based accounting’ to quantify their greenhouse gas emissions. This approach counts emissions from all activities that happen within a country’s territory – which means the emissions from goods manufactured elsewhere and then imported are not included.

It can be argued that if a country can produce certain types of goods more efficiently with lower emissions than other countries, this may be the preferred situation. From a global perspective, climate policy should recognise the advantage of producing goods where they can be made with lower emissions. But there is an important corollary to this outlook: considering only the production-based emissions of countries is not enough to address a global climate crisis. We need to consider our consumption as well as our production and assess whether our consumer demands in the UK are generating emissions here and elsewhere that are in line with a sustainable future.

In truth, we should account for both consumption-based emissions and production-based emissions. Accounting for our consumption fully would assess the greenhouse gases emitted in the production of all the goods and services we consume – imported goods as well as everything that is produced and then consumed in the UK.

We don’t count emissions from imports because they are harder to quantify than the emissions we produce in the UK. It requires tracing the point of origin of imported products, often in places with less stringent emission inventories. The most convenient thing to do is simply ignore the emissions we generate beyond the boundaries of our nation state – despite the shared atmosphere above us.

How big is the elephant in the room? In 2016, the production-based emissions from UK produced goods and services (consumed by UK residents but not including exports) and from greenhouse gas emissions produced from household use of fuel and electricity accounted for 421 mt CO₂e (million tonnes of equivalent carbon dioxide). The total emissions generated from the stuff we import accounted for 353 mt CO₂e. These figures are too big to comprehend: instead, hold onto the fact that we choose not to account for around 45% of the total emissions that we are responsible for.

If we cannot partition the atmosphere,  we should not ignore the greenhouse gas emissions we generate simply because they are not immediately overhead.

— source+©: https://carboncopy.eco/blog/dont-just-consume-it-count-it