This blog will provide you with general strategies for understanding and responding to climate action. A useful place to start is: Which climate protection measures work at the root cause? And which ones might be rather ineffective? To answer this, we first need to look at the main sources of greenhouse gas (GHG) emissions [1-4] and – most importantly – their relative proportions.
That is, before we look at solutions, we do the bean-counting. This is not surprising: it is often a good strategy to first estimate the quantities and only then explore solutions.
- The main driver of climate change is carbon dioxide (CO2). About 85% of global CO2 emissions come from the burning of coal, gas and oil.
- The rest of CO2 emissions are mainly caused by land use change such as clearing for agriculture and logging.
- Fossil fuels also cause about half of global methane (CH4) emissions, the second driver of climate change.
- The other half of methane emissions are mainly caused by the way we treat waste technologically, by raising livestock and the wet cultivation of rice.
- There are also other types of greenhouse gases, but their influence is small compared to CO2 and methane.
Although these quantities are well-known, it is often overlooked that most GHG emissions are caused by technology. Overlooked sometimes by those who advocate behavioural and systemic change as the main mitigation strategy:
Let’s take a closer look at the wide variety of global CO2 emissions to get a sense of the relative proportions:
About half of the technology-related CO2 emissions come from power plants that run on coal and gas.
That is why renewable energies are a hot topic . They can reduce our problem by half. And what can nuclear power do, for example? We’ll cover that in a later blog article.
Almost a quarter is caused by traffic, with cars and trucks making up the largest share:
That is why electric cars and trucks are a hot topic. Shipping and rail contribute rather little, even though they carry by far the most “weight times distance”. Planes make about half the contribution of trucks, but remember that the contrails can also enhance global warming, and that very few people in the world travel by plane, so air travel has the potential to grow rapidly.
Almost a quarter are caused by industry, of which almost 3/4 are caused by the generation of heat:
The contribution of heat is represented by the lighter shade in each case .
Right or wrong with allocation?
You may have seen that quite different CO2 values are sometimes allocated to different sectors in industry. This is because emissions can generally be allocated in different ways. I choose the categories according to where the major responsibility lies – and therefore also the opportunities. For example, industry buys electricity from electricity suppliers and is not directly responsible for whether or not the electricity suppliers have enough renewable energy in their portfolio. So, I attribute the emissions associated with electricity use to the power plants and not to industry. But the fact that people in industry heat with fossil fuels is their decision, driven by factors that directly affect these people.
There is no right or wrong to which categories emissions should be assigned. Just be careful that there is no double counting, and that no major emissions are ignored.
But if the responsibility for heat generation is handed over to industry, one may ask how industry is supposed to generate renewable heat for its many processes? Humans should mostly stop heating by burning something and move to generating heat by heat pumps, solar heat, geothermal, arc furnaces and other sources. This transition is a topic for an upcoming blog article.
The next category that contributes significantly to global CO2 emissions is the building sector:
You may notice that often many more emissions are attributed to buildings: Electricity from coal-fired power plants to run the fridge, for example. You could go on like this and assign everything that goes into the house, like consumer goods and food, and end up saying that in Singapore 90% of CO2 emissions are caused by buildings. Would such a categorisation make sense? That would put all the responsibility on the occupants of the building. Are they responsible for having a limited choice of fridges? I think not, and that is why I assign the manufacture of fridges, including the sourcing of raw materials, to industry, and I assign the emissions associated with running the fridges to the electricity industry. And I assign the CO2 emissions associated with the construction phase of the buildings (called “grey energy”) to the industrial sector, such as cement production and also to transportation by trucks or excavators, etc.
I argue for allocating CO2 emissions to where the major responsibility lies, because that gives us a mindset that is effective for CO2 mitigation.
Sometimes, of course, the main responsibility cannot be clearly assigned because it may be shared by different actors (we will explore the push-an-pull between industry and consumers with interesting data in the next newsletter). But in terms of finding effective CO2 reduction strategies, I think it is the best we can do. For example, running the gas cooker is the primary choice of the people who live in the building, and therefore attributed to the building, because they could cook with an electric cooker and hope that the electricity providers have renewable energy in their portfolio.
Let’s have a closer look at cooking with gas (the main contribution from appliances). For cooking, about 1/3 of the world’s population  uses wood (or derivatives like charcoal). Of their harvest, about 1/3 is unsustainable , leading to forest degradation or deforestation and thus to net CO2 emissions about as high as those from gas cooking in modern households. This is assigned to the land use change category in the following graph:
About 15 % of global CO2 emissions is caused by land clearing for agriculture and settlements and by deforestation.
These CO2 emissions are not primarily caused by technology , although technology certainly plays a role, such as in cheap transport: it enables rich and middle-income countries to import large quantities of feed crops for their industrial livestock farming . The poultry industry consumes about 40% of the world’s feed, the pig industry about a third – and it is important to note that these account for about half of the biodiversity loss. This illustrates that the different categories we have looked at are not separate entities. Their coupling can either increase the complexity of mitigation strategies or be a multiplier for mitigation actions, depending on how we implement mitigation actions. This graphic  gives an impression of this:
The cattle in this graph emit mainly methane, not CO2, but often greenhouse gases other than CO2 are given as “CO2 equivalent” so that all greenhouse gases can be shown in one graph.
The case of methane
To conclude our bean counting, let’s take a quick look at methane emissions:
As mentioned, almost half of methane emissions come from fossil fuels (blue).
Another large share comes from waste treatment, which is also primarily technological, as methane emissions from decaying waste could be avoided.
Finally, cattle farming for meat, mainly for rich countries, is the remaining largest share, followed by wet rice farming, mainly for middle-income countries. In contrast, breeding pigs and chickens causes mainly CO2 emissions and biodiversity loss through land use change, as we have seen above.
Sheep, goats and other cattle play a small role and may be difficult to reduce because many poor families in regions with seasonal weather or poor soils rely on them to balance both their food source and income. It would not be fair to push them to reduce methane. But climate justice is a topic for another blog article.
Is your area explicitly in these charts? Or does it play only a small role compared to others? If so, you or your colleagues might be tempted to think that there is no urgent need for change. I have three arguments for you:
- We are not on track to fulfil the Paris Agreement. This agreement is not binding, nor are there penalties for missing the targets. In this situation, the small savings from many small actors are just as important as the big chunks from big actors.
- Many of us assume that once the Paris Agreement is met, the job is done. But think about it. By then, the polar ice will be melting even faster than today, hurricanes and droughts will occur more often, and so on. We are not even sure  whether the temperature will stabilise quickly or if there will be an overshoot until it stabilises . Therefore, it is safe to say that every bit of CO2 we emit now will have to be removed from the atmosphere by our children. This will be technically feasible, but it will be much more burdensome for them and cause them more economic pain than your current choices (more on this in a later blog article).
- If our planet were the size of an egg, the atmosphere would be thinner than the eggshell. Accordingly, releasing greenhouse gases into the atmosphere has a very effective impact on our climate. We are more fragile than we think.
I finish with the bottom line:
The main point of today’s blog is: We emit most of the greenhouse gases because we use inadequate technologies.
Many of us know that these technologies are getting us into big trouble, but the immediate question is: can we solve these difficulties by changing technology? This is not obvious. For example, coal-fired power plants require quite little material per energy produced : for the machinery to extract the coal, for transport and for the power plant. In contrast, solar radiation arrives rather diluted and must be captured by large areas of solar cells, which means more material. The same is true for wind turbines. If we shut down coal-fired power plants and replace them with renewables, do we go from a climate problem to a material problem? With that to an environmental problem and even a biodiversity problem? Do we go from the frying pan into the fire when we try to control the climate mainly through technology?
In the next blog article, we will begin to explore this question in detail.
Meanwhile, I wish you an exciting time.
P.S. Change is happening anyway. Make it yours.
 M. Roser et al., “Our World in Data,” Oxford Martin School, University of Oxford, UK, with the Global Change Data Lab (2021). https://ourworldindata.org/
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 L. Höglund-Isaksson, A. Gómez-Sanabria, Z. Klimont, P. Rafaj, and W. Schöpp, “Technical potentials and costs for reducing global anthropogenic methane emissions in the 2050 timeframe –results from the GAINS model,” Environmental Research Communications 2(2), p. 25004, 2020. http://dx.doi.org/10.1088/2515-7620/ab7457
 IRENA, “World Energy Transitions Outlook: 1.5°C Pathway,” Abu Dhabi, 2021. https://irena.org/publications/2021/March/World-Energy-Transitions-Outlook
 S. Bonjour et al., “Solid Fuel Use for Household Cooking: Country and Regional Estimates for 1980–2010,” Environmental Health Perspectives 121(7), Jul. 2013. https://doi.org/10.1289/ehp.1205987
 R. Bailis, R. Drigo, A. Ghilardi, and O. Masera, “The carbon footprint of traditional woodfuels,” Nature Climate Change5(3), 266–272, Mar. 2015. https://doi.org/10.1038/nclimate2491
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 WWF, “Appetite for destruction,” Oct. 2017. https://wwfint.awsassets.panda.org/downloads/wwf_appetitefordestruction_full_report_web_0_1.pdf
 N. Bowles, S. Alexander, and M. Hadjikakou, “The livestock sector and planetary boundaries: A ‘limits to growth’ perspective with dietary implications,” Ecological Economics 160, 128–136, Jun. 2019. https://doi.org/10.1016/j.ecolecon.2019.01.033
 B. H. Samset, J. S. Fuglestvedt, and M. T. Lund, “Delayed emergence of a global temperature response after emission mitigation,” Nature Communications 11(1), 3261, Dec. 2020. https://doi.org/10.1038/s41467-020-17001-1
 A. H. MacDougall et al., “Is there warming in the pipeline? A multi-model analysis of the Zero Emissions Commitment from CO2,” Biogeosciences 17(11), 2987–3016, Jun. 2020. https://doi.org/10.5194/bg-17-2987-2020
 IEA, “The Role of Critical Minerals in Clean Energy Transitions,” Paris, May 2021. https://www.iea.org/news/clean-energy-demand-for-critical-minerals-set-to-soar-as-the-world-pursues-net-zero-goals
Data sources for charts
I complied the proportions of CO2 emissions of various sectors mainly from data of Ref.  and , the subsectors and other details are extracted from the supplement of Ref.  but by adjusting the values to recent total emissions. These values are therefore approximate. The methane chart is a compilation from data in the supplement of Ref. , and the food chart from data in Ref. . The CO2 and NH4 records during the past 800’000 years are from the Antarctic ice core project, downloadable from https://www.epa.gov/climate-indicators
Icons were bought or freely available from: Yodke67 on dreamtime.com (goat), Amru on iconscout.com (heating), Rutmer Zijlstra on thenounproject.com (milk cow), Ronnica on dreamtime.com (sheep), rice bowl from icons8.com, and the remaining icons from Microsoft.
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