Are there other greenhouse gases?

Carbon dioxide (CO2) is just one of many different types of greenhouse gas which contribute to climate change [2]. Although CO2 does make up 76% of greenhouse gas emissions (measured in CO2-eq*), there are two others that we must not forget about [3]:

1) Methane (CH4) is a much more “potent” greenhouse gas than CO2: over 100 years, one methane molecule has the same warming impact as 28 molecules of CO2 [7]. This is because methane is a more powerful greenhouse gas, but lasts on average for only 12 years before breaking down, compared to 5-200 years for CO2 [8].

Methane accounts for about 17% of CO2-eq emissions [3]. A lot of people think that cows fart methane [9] – in fact, they burp it [10]! However, agriculture as a whole is only responsible for about 39% of methane emissions [4]. It may be a surprise to you that energy generation releases a similar amount of methane, at 36% [4].

2) Nitrous Oxide (N2O) is an even more powerful greenhouse gas than methane – it’s 9x stronger over a 100-year period [7]! Fortunately, we don’t release that much of it, so it only accounts for about 7% of CO2-eq emissions [3]. 72% of this is from agriculture [5], primarily from fertilisers and manure [1].

Whilst altering what we feed cows can reduce CH4 emissions [11], to reduce emissions more substantially we need to have fewer cows [12]. N2O emissions can be reduced by, for example, using only as much nitrogen fertiliser as a crop will consume [13], and using alternatives to fertiliser such as leguminous plants (like peas and clover) which take nitrogen out of the air and release it into the soil when they die [14,15].

*CO2-eq = CO2-equivalent emissions: the amount of CO2 that would cause the same amount of warming as a given amount of another greenhouse gas, over a 100-year time span [6,7].

References

[1] https://www.nature.com/articles/s41558-019-0642-2

[2] https://ourworldindata.org/co2-and-other-greenhouse-gas-emissions See: Emissions of other greenhouse gases

[3] https://ourworldindata.org/co2-and-other-greenhouse-gas-emissions See: Greenhouse gas emissions by gas source

[4] https://ourworldindata.org/co2-and-other-greenhouse-gas-emissions See: Methane (CH4) emissions by sector

[5] https://ourworldindata.org/co2-and-other-greenhouse-gas-emissions See: Nitrous oxide (N2O) emissions by sector

[6] https://www.ipcc.ch/site/assets/uploads/2018/02/AR5_SYR_FINAL_Annexes.pdf See: CO2-equivalent (CO2-eq) emission

[7] https://www.ghgprotocol.org/sites/default/files/ghgp/Global-Warming-Potential-Values%20%28Feb%2016%202016%29_1.pdf See: GWP values for 100-year time horizon, Fifth Assessment Report (AR5)

[8] https://archive.ipcc.ch/ipccreports/tar/wg1/016.htm See: table

[9] https://www.theguardian.com/environment/2019/jun/29/cows-farts-children-climate-questions-answered

[10] https://climate.nasa.gov/faq/33/which-is-a-bigger-methane-source-cow-belching-or-cow-flatulence/

[11] https://academic.oup.com/jas/article-abstract/94/5/2024/4701661

[12] https://www.sciencedirect.com/science/article/pii/S0166111698800162

[13] https://www.tandfonline.com/doi/full/10.1080/00380768.2012.733869 See: Reducing N fertilization

[14] http://www.ini2016.com/pdf-papers/INI2016_Salazar_Monica.pdf

[15] https://www.tandfonline.com/doi/full/10.1080/00380768.2012.733869 See: Using biological N fixation to provide N inputs

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