Main sources of Emissions

To understand how we can limit climate change, we must first of all know which are the main sources of greenhouse gases. This is an important first step, because otherwise we may try to make adjustments that have only little effect on climate change. The following figure shows greenhouse gas emissions by category:

Emisions by industry
Greenhouse gas emissions by industry (after EPA [1] and IPCC [2]).

When we look at this figure, it becomes clear that most emissions are a direct result of our individual choices, for example, the choice of our electricity provider and heat supplier (25% in total), the choice of our means of transportation (e.g. air travel, car, 14%), or our food choices.

That means, when summing up all emissions produced by our daily lifes, the food we consume, housing, travel to work, picking up children, doing trips and vacations, each person contributes to roughly 65% ​​of all emissions. Taking in addition the purchase of industrial goods, e.g. cell phones, washing machines, small appliances, etc., into account (21%), this adds up further, until we eventually approach the 100% mark.

Hence, it is above all our own choices, such as the choice of electricity provider, our diet and the choice of our means of transport, which mainly contribute to climate change. So what can we do to reduce our carbon footprint?


The main source of greenhouse gas emissions is the generation of electricity and heating (25%). Of course nobody can live without electricity. But there are electricity suppliers offering 100% renewable energy. Meanwhile, solar power is the cheapest form of energy [3], hence switching to a provider with 100% renewable energy may even pay off financially (all formalities regarding a supplier change are usually covered by the green energy providers, so you don’t have paperwork). Often, these suppliers also offer biogas or by reforestation climate-neutral natural gas.

Food choices

In second place is agriculture and forestry with 24% of global emissions. The agriculture sector is particularly interesting, as each one here has great levers. In agriculture, however, the major emissions are not CO2, but the substances methane (CH4, which is mainly produced in animal husbandry) and nitrous oxide (N2O, which is produced by the use of fertilizers) [4]. These two substances heat the atmosphere many times more than CO2 and are therefore especially dangerous. Methane is 25 times more effective than CO2 and nitrous oxide is 298 times more effective than CO2 [5].

Nitrous oxide is mainly released by fertilization with nitrogen fertilizers, which is used in conventional agriculture. Since synthetic fertilizers are not used in organic farming (instead, sustainable soil management and natural fertilization help to keep the soil fertile), greenhouse emissions in organic farming are up to 50% lower than in conventional agriculture [4]. The consumption of products from organic farming therefore already results in a significant reduction in greenhouse gas emissions.

Another very powerful lever is our choice of food. In particular animal products result in high emissions, especially with regard to methane. The production of animal products (meat and dairy products) accounts for 80% of the greenhouse gas emissions from food production, as shown in the following figure [6,7]. A similar picture emerges, when looking at the emissions per serving: For example, the emissions for one serving of beef compared to one serving of legumes are about 60 times higher (interestingly, both have a similar protein content (depending on the type of bean, e.g. about 20% for black beans and also about 20% for beef [8]). Hence the choice of our source of protein has a very strong effect on our greenhouse gas emissions.

Emissions due to food choice
Left: Greenhouse gas emissions for different types of food. Right: Emissions per serving.
(after Heller M., Keoleian G. 2014 [6,7])

So you can save up to 50% of emissions by the consumption of organic products and up to 80% of the emissions caused by agriculture by reducing animal food. Furthermore, avoiding consuming animal products will also result in significant health benefits (risk of heart attack, risk of diabetes type II, vascular diseases, etc. [9]), for example, diabetes type II can be cured when excluding animal products from the diet (due to unsaturated fatty acids). In particular processed meat (such as sausage or ham) has been found to be cancerogenous [10].

Humans and their livestock now represent 96% of all land living mammals (wild mammals compose only 4% of the biomasse of mammals, [11]). Of these 96% only 36% are humans and the rest (60%) represents livestock. This demonstrates why the meat and dairy industry has a significant effect on our greenhouse gas emissions and results in other ecological issues (such as a loss of habitat, extiction of species, etc.).


The category transportation is responsoble for only about 14% of global emissions (behind manufacturing goods, 21%), but since it is relatively easy to avoid emissions by transportation, this category is discussed first. In addition, emissions from the transport sector in industrialized countries are often significantly higher than 14% and emissions have been rising steadily during the last years [4].

The means of transportation causing most emissions is the aircraft. Not only are the largest quantities of CO2 emitted by passenger flights, but planes also emit various other greenhouse gases than CO2, which are particularly effective because they are emitted at great heights [12]. After the aviation, passenger cars represent the second-worst means of transportation. Buses and trains are much more climate-friendly. Thus, when traveling by air about 20 times more CO2 is produced than when travelling by train (covering the same distance). The approximate CO2 emissions of different means of transport are shown in the following figure (eact numbers may vary, e.g. depending on the type of aircraft or the number of people traveling in a car) [13].

CO2 emissions by means of transporation per passagier and kilometer (Source: EEA).

The effect of air travel is particularly high for developed countries, for example, travel by EU citizens accounts for 35% of all air travel emissions [14]. Furthermore, we fly more and more often: From 2005 to 2017 aviation in the EU increased by 60% per passenger[14]. This resulted in emissions of 163 million tonnes of CO2 and 839 thousand NOx in the EU in 2017 [15].

In order to illustrate the emissions due to transportation, three persons living near Berlin are compared below (daily commuting 25 km one-way to their work, 200 days per year). One person commutes to work by train (14 g CO2 per km) and travels once a year to Spain (Barcelona). The second one takes a small passenger car to work (104 g CO2 per km) and flies once a year to the US (New York). The third one drives an SUV (a large car) to work (158 g CO2 per km) and travels three times a year by plane (Barcelona, ​​San Francisco, Bali). When calculating a CO2 balance for these persons on the basis of the previous graph (see above) the following picture emerges:

Commutes byDistance to workCO2 due to commutingAir travel per yearFlight distance CO2 due to air travelSum CO2
Person 1Train25 km140 kgBarcelona1,800 km513 kg653 kg
Person 2Small car25 km1,040 kgNew York6,400 km1,824 kg2,864 kg
Person 3SUV25 km1,580 kgSan Franciso, Bali20,600 km5,871 kg7,451 kg

A commuter with a large car (SUV) booking two long-distance flights a year causes more than 10 times more CO2 emissions (in total 7,451 tons) than a commuter who commutes by train and only flies within Europe once a year (0.653 tons). Following the lifestyle of the person with the lowest emissions does not necessarily mean a restriction of lifestlye. The train ride may allow this person to read books that she/he could otherwise not read or to do other things that the SUV driver can only do after work, when he returns home. All three persons may spend the same number of days abroad. Person 1 might spend a week hiking in the Pyrenees, then stay a week in Barcelona and finally hang out at the beach for another week. Instead, Person 3 may spend a week in San Franciso and two weeks in Bali, losing a few days per trip due to jet lag.

Industry (production of goods)

The industrial sector, i.e. the manufacture of goods, such as consumer goods, accounts for about 21% of greenhouse gas emissions [1]. Although consumers have no direct influence on the choice of production methods, they can choose whether and what they buy. Particularly large amounts of greenhouse gas emissions are generated in the manufacture of cement and metals, followed by the production of chemicals (such as plastics, fertilizers) [16]. Emissions can be avoided by buying quality products that last a long time, or by asking yourself if you really need a new product to be happy. Likewise, it helps if you give products that you no longer need away or if you sell them instead of simply throwing them away or to buy used goods or clothes in the first place (for example, it is easy to find barely used children’s clothes second hand, since the children grow faster than it would take to wear clothes off).

In recent years a reduction of greenhouse gas emissions has increasingly being attempted by the introduction of a CO2 tax (in some countries since the 1990s) [17]. The success varies with the amount of tax. Successes are lower in countries with a lowe CO2 tax. In addition, particularly CO2 intensive economic sectors are often excluded from such a tax.


In summary, each individual can easily avoid 50% to 80% of CO2 emissions without a significant change of quality of life. This can be achieved, for example, by a change of electricity provider, a slight change in eating habits (which also results in significant health benefits) and a considerate choice of our means of transportation, adapted to a 21st century life style, or finally by a different holiday planning and more informed purchasing decisions.


  1. US EPA. Global greenhouse gas emission data. Online
  2. IPCC 2014. Climate Change 2014 – Mitigation of climate change. Working Group III contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Online
  3. Frauenhofer Institut 2018. Photovoltaik und Onshore-Wind sind günstigste Technologien in Deutschland. Online
  4. Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB) 2018. Climate Action in Figures. Facts, Trends and Incentives for German Climate Policy. 2018 edition. Online
  5. Solomon D. et al. 2007. Climate Change 2007: The physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, Chapter 2, Table 2.14. Online
  6. Heller M., Keoleian G. 2014. Greenhouse gas emissions estimates of U.S. dietary choices and food loss. Journal of Industrial Ecology 19: 391-401. Online
  7. Center for Sustainable Systems, University of Michigan. 2018. Carbon Footprint Factsheet. Pub. No. CSS09-05. Online
  8. Boher B.M. 2017. Review: Nutrient density and nutritional value of meat products and non-meat foods high in protein. Trends in Food Science & Technology 65: 103-112. Online
  9. Eine sehr gute Übersicht zu dem Thema (mit wissenschaftlichen Quellen) gibt es unter
  10. Behrens G. et al. 2018. Cancers due to excess weight, low physical activity, and unhealthy diet. Deutsches Arzteblatt International 115: 578-585. Online
  11. Bar-on Y. et al. 2018. The biomass distribution on Earth. Proceedings of the National Academy of Sciences 115 : 201711842. Online
  12. Wikipedia Artikel über den Umwelteinfluss des Flugverkehrs. Online
  13. European Environment Agency (EEA) 2016. CO2 emissions from passenger transport. Online
  14. Sims R. et al. 2014: Transport. In: Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Edenhofer, O. et al. (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Online
  15. European Aviation Safety Agency (EASA) 2019. European Aviation Environmental Report 2019. Online
  16. Fischedick M. et al. 2014. Industry. In: Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Edenhofer O. et al. (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
  17. Mardones C., Flores B. 2019. Effecctiveness of a CO2 tax on industrial processes. Energy Ergonomics 71: 370-382. Online

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